American History & Society — A Background Guide

For a long time, history books were about the public lives of men: wars and governments. Then, in the late 1960s and the 1970s, came second-wave feminism, the women’s movement of those years. Its slogan was “the personal is political”, meaning that private life is political too. That slogan is why feminist theory values women’s own stories.

Alongside the movement, women’s history became a proper academic field. Because the old history was about men in public life, its scholars turned to new sources: diaries, letters and interviews. Oral history means recorded interviews with people who saw events for themselves. Think of recording a grandparent’s memories of Partition before they fade.

In America, Studs Terkel made oral history popular, for example with his book “The Good War” in 1984. Other projects interviewed women who had worked in factories during the Second World War. In that war, millions of men were in uniform. About 6 million more women took paid jobs, many in defence plants, the factories that made war goods.

Government posters, with “Rosie the Riveter” and the slogan “We Can Do It!”, made this work look glamorous. After 1945, most of these women were laid off or pushed back into the home. Today every American knows Rosie, and the familiar story that the war “brought women into the workforce”.

In August 1920, the 19th Amendment was added to the US Constitution. It forbids denying anyone the vote “on account of sex”. It ended a 72-year campaign that began at Seneca Falls in 1848. Its leaders included Susan B. Anthony, Elizabeth Cady Stanton, Carrie Chapman Catt and Alice Paul.

The campaigners, called suffragists, had made a promise. Women would vote together as a moral bloc, a women’s “vote bank”, as Indians might say. They would clean up politics, ending corruption and closing the saloons, or bars. The promise was tied to the temperance movement against alcohol, and to Prohibition, the national ban on alcohol that came in 1919.

In fact, once women could vote, they voted much like the men of their own class, region and party. So critics declared suffrage a “failure”. Jane Addams, a leading Progressive reformer who founded Hull House in Chicago, made a quip about this charge. Its point was that nobody asks whether men’s suffrage has failed.

The early 1920s brought some wins. The Sheppard–Towner Act of 1921 gave federal money for the health of mothers and babies, until it lapsed in 1929. The Cable Act of 1922 gave married women their own citizenship.

After about 1925, the mood turned conservative and pro-business, and reformers faced “Red Scare” attacks, born of a fear of communism. Reformers also split over the ERA, the Equal Rights Amendment proposed by Alice Paul in 1923. Some backed it, and others backed protective labour laws for women.

Today, Americans learn that 1920 is the year women got the vote. They know Susan B. Anthony, who was once on a dollar coin, and the “flapper”, the popular image of the 1920s. She stood for a younger generation that saw organised feminism as old-fashioned. American campaigners called themselves “suffragists”, and “suffragette” was mainly a British word.

Antebellum means “before the war”. Americans use it for the years from about 1815 to 1861, before the Civil War. In those years, two big parties fought for power. Historians call this the Second Party System, and it ran from about 1828 to 1854.

On one side stood the Democrats of Andrew Jackson, who spoke for farmers, states’ rights and the “common man”. On the other stood the Whigs, founded in 1834 to oppose “King Andrew”. They backed Henry Clay’s plan of tariffs, or taxes on imports, plus a national bank and new roads and canals. They were strong among middle-class, evangelical Protestant reformers.

In 1840, William Henry Harrison ran the “Log Cabin and Hard Cider” campaign, with the slogan “Tippecanoe and Tyler Too”. It was the first modern mass campaign, with parades, songs, barbecues and huge rallies, much like an Indian election season. About 80% of eligible voters turned out, and women came to the rallies and sewed banners. This was the “new American political nation”.

By the 1840s nearly all white men could vote. Women, enslaved people and most free Black men could not. The organised “woman’s rights movement” began at Seneca Falls in 1848. Whig “female politics” was different: women took part as moral supporters of a party and as influencers, not as people seeking the vote.

The Whigs fell apart over slavery in the mid-1850s, and the Republican Party replaced them. Today Americans know Andrew Jackson, whose face is on the $20 bill, but they know the Whigs only vaguely. In school textbooks, the 1840 campaign is a standard “first” of mass politics.

Picture America in the 1820s. Industry is growing, and with it a new middle class. Paid work is moving out of the home. So people come to see the home and the world of paid work as separate spheres.

In 1966 the historian Barbara Welter gave this age’s ideal of womanhood a name: the cult of true womanhood, also called the cult of domesticity. The true woman was pious, or deeply religious, and pure. She was also submissive, or obedient, and domestic, devoted to her home.

Benevolent work, or organised charity, took many forms. Volunteers ran orphan homes and Sunday schools, campaigned against prostitution, and fought alcohol through the temperance movement. The Women’s Christian Temperance Union was founded in 1874.

Others worked for abolition, the ending of slavery, or for relief in the Civil War. In that war, a giant civilian relief agency, the US Sanitary Commission, ran largely on women’s volunteer labour.

The law set limits. Under coverture, a married woman could not own property or sign contracts. So charitable societies got charters, acts of state legislatures that made them legal bodies, much like registering a society or a trust in India. They also used men as trustees, or chose single women and widows as officers.

Today, students in APUSH, an advanced US history course in high school, memorise a sequence. First came Republican Motherhood, the duty of mothers to raise good citizens, then the Cult of Domesticity, then Seneca Falls. They also learn about two Civil War nurses. Clara Barton founded the American Red Cross in 1881, and Dorothea Dix also reformed asylums for the mentally ill.

Feminists have long argued over one question. Should women be treated the same as men? Or should their differences, such as motherhood, be valued and protected? This is the equality-or-difference debate.

England and America share a long tradition of rights. It runs from Magna Carta in 1215, through the English Bill of Rights of 1689, to the US Declaration of Independence in 1776. Along the way, John Locke argued that every person has natural rights to life, liberty and property. This is the Anglo-American rights tradition.

Feminists in this tradition argued that women are individuals with the same rights as men. Mary Wollstonecraft made the case in A Vindication of the Rights of Woman in 1792. At Seneca Falls in 1848, campaigners declared that “all men and women are created equal”. J.S. Mill followed with The Subjection of Women in 1869.

On the continent of Europe, especially in France, another tradition stressed the family, motherhood and a woman’s duty to the nation. It led to maternalist policies that support mothers, such as paid maternity leave and family allowances. Europe has such policies, and the US largely lacks them. The US has no national paid maternity leave, and a 1993 law, the FMLA, guarantees only unpaid leave.

The same split came back in America in the 1920s. Supporters of the ERA, the Equal Rights Amendment, wanted women treated the same as men. Supporters of protective labour laws wanted special rules for women workers, such as limits on their hours. Today, Americans tend to assume that “equal rights” is the only kind of feminism.

Picture Florence in the 1600s. Its golden age, the Renaissance, is over, and the Medici family now rule the city as Grand Dukes. But Florence still lives on cloth. Its wool and silk sell all over Europe. Two powerful guilds, one for wool and one for silk, decide who may learn the trade, who may join it, and what counts as good work.

Making fine cloth takes several steps. First, workers comb or card the raw fibre to untangle it. Spinners then twist it into yarn, and weavers turn the yarn into cloth on a loom. Last, the cloth is finished and dyed. One luxury product is taffeta, a crisp, smooth silk.

Not all of this work needs a workshop. Under the putting-out system, a merchant drops off raw material at a worker’s home and later pays for each finished piece. So weaving can be done at home.

Now jump forward three hundred years. Economists want to know why women earn less than men, and two answers stand out. The first is human capital theory, made famous by the American economist Gary Becker, who won the Nobel Prize in 1992. It treats skills like savings in a bank: the more training you put in, the more you earn later. A worker who expects long breaks from work puts in less, so she earns less.

The second answer is crowding, an idea of the economist Barbara Bergmann in the 1970s. Imagine a town where women may enter only a handful of trades. They all pile into those few jobs, so employers can pay them less. Men’s trades face less competition, so they pay more. It is simple supply and demand.

American economics students still meet these two answers when they study today’s gender pay gap. One side stresses choices and skills. The other stresses segregation and discrimination.

Sarah Eisenstein lived from 1946 to 1978. She died young, and her work was left unfinished. Her book came out after her death, in 1983. Its full title is Give Us Bread but Give Us Roses: Working Women’s Consciousness in the United States, 1890 to the First World War.

Picture America between 1890 and 1917. Millions of young single women work for wages, and many are immigrants who are Jewish, Italian or Irish. They sew in garment shops, run machines in textile mills, sell in department stores or work as servants in other people’s homes. Think of the young women in garment workshops in Indian cities today.

These years saw famous strikes. In 1909, shirtwaist makers in New York, who sewed women’s blouses, walked out in the “Uprising of the 20,000”. In 1912, textile workers in Lawrence, Massachusetts, held the “Bread and Roses” strike. The Women’s Trade Union League, founded in 1903, linked middle-class reformers with the workers.

On 25 March 1911, fire swept through the Triangle Shirtwaist Factory in New York. It killed 146 people, mostly young immigrant women trapped behind locked doors. The disaster led to factory-safety laws. Every US history textbook treats the Triangle fire as a turning point in labour law.

Picture Lowell, Massachusetts, between the 1820s and the 1840s. It was America’s first big factory town. Young women from New England farms, the mill girls, ran its textile machines. They lived in company boarding houses, a bit like a college hostel attached to the mill.

From about 1880 to 1930, the service sector, work that sells services rather than goods, grew fast. Department stores filled with “shopgirls”. The typewriter, which arrived in the 1870s, turned office work from a man’s job into a woman’s. By 1900, telephone operators were almost all women.

Yet until about 1940, the largest job for women, especially immigrant and Black women, was domestic service. These women worked as maids, cooks and servants in other people’s homes.

During World War II, when the US was at war from 1941 to 1945, millions of women took jobs in war plants. “Rosie the Riveter” became their symbol. When the men came home, many were laid off, and the baby boom followed.

Marxist and liberal thinkers, such as Friedrich Engels, had expected industrial wage work to emancipate women, or set them free. The gap between that hope and reality is called the “unfinished revolution”.

Today, the Lowell mill girls and Rosie the Riveter are standard textbook images. Many fields are still heavily sex-typed: most nurses and teachers are women, and most engineers are men. This sorting of jobs by sex, called occupational segregation, is a major driver of the gender pay gap.

The US Constitution, in Article I, requires a census, or count of the people, every 10 years. The first was held in 1790. Its purpose is to divide seats in the House of Representatives, America’s Lok Sabha, among the states. Until 1865, an enslaved person counted as only “three-fifths” of a person for that purpose.

From 1790 to 1840, the census named only the head of household. Everyone else in the home was counted by age, sex, and free or enslaved status. The household, not the individual, was the economic unit. A wife’s work, and her children’s, was credited to the head.

The 1850 census was the first to list every free person by name. It recorded each person’s age, sex and birthplace, and for men it also recorded an occupation. Enslaved people went on a separate “slave schedule”, listed under their owners’ names. Their own names were usually left out.

Counting women’s work is still a matter of debate. Today, unpaid housework and care are left out of GDP, the total value of what a country produces. So a homemaker who cooks and cares for a family all day adds nothing to it. Americans fill in the census once a decade, and they learn about the Three-Fifths Compromise in school.

Between the 1940s and the 1980s, Latin America urbanised very fast. In other words, its people moved from the countryside into the cities. Today it is about 80% urban, one of the most urbanised regions on Earth. Many of the poor live in large informal settlements, such as Brazil’s favelas, much like the slums of Mumbai.

Poor women who moved to the cities often worked as domestic servants in middle-class homes. In Brazil, this has historically been the largest job for poor women in the cities. Others worked in the informal sector, the world of small, unregistered work such as street vending and laundry. Poor men relied on unstable building work and day labour.

To survive, the poor build reciprocal exchange networks. Relatives and neighbours swap childcare, loans and food, and each favour is returned in time. A classic study of this is Larissa Lomnitz’s 1977 work on a shantytown in Mexico City.

Another kind of tie links people who are not equal. In a patron–client tie, also called clientelism, a richer patron gives loans, jobs or medical help. In return, the poorer client gives loyalty and service. These ties are strengthened by compadrazgo, or godparenthood.

The AFL, the American Federation of Labor, was founded in 1886 and led by Samuel Gompers. It was made up of craft unions, each for skilled tradesmen in one craft, such as carpenters or machinists. It often shut out women, Black workers and the unskilled.

In 1935, John L. Lewis led the founding of the CIO, which began as a Committee and became the Congress of Industrial Organizations in 1938. It built industrial unions: one union for all the workers in an industry, such as autos, steel or rubber, whatever their skill. It was far more inclusive. The two groups merged as the AFL-CIO in 1955.

The Wagner Act of 1935, part of the New Deal, guaranteed workers the right to organise and to bargain collectively. That means negotiating pay and conditions as a group. Union membership roughly quadrupled, to about 14–15 million by 1945.

Two strikes became landmarks. The first was the 1934 strike in Minneapolis by the Teamsters, the truck drivers’ union. There, the local community and the women’s auxiliaries, or support groups, were crucial.

The second was the 1936–37 sit-down strike in Flint by the United Auto Workers, or UAW, against General Motors. The workers sat down inside the plants and refused to leave, a bit like a dharna inside the factory. A Women’s Emergency Brigade supported them.

What decides a person’s class? For Karl Marx, it was your relation to the means of production, the land, tools and factories used to make goods. You either owned them or worked for those who did. Max Weber added status and power, while American sociologists usually measure socioeconomic status by income, job and education.

Married women also lived under coverture. In 1765 the English legal scholar William Blackstone wrote that “the husband and wife are one person in law”. A wife could not own property, sign contracts, keep her wages or sue.

Married Women’s Property Acts, which began to chip away at coverture, started in Mississippi in 1839 and New York in 1848. No women voted anywhere in the US, except propertied women in New Jersey from 1776 to 1807.

In this period, “free” women means women who were not enslaved. Enslaved women lived in an entirely different condition. Later scholars studied the differences among women, by class, race and ethnicity. This work led to intersectionality, a term coined by Kimberlé Crenshaw in 1989.

In 1325, a people called the Mexica, better known as the Aztecs, founded the city of Tenochtitlan on an island in Lake Texcoco. Today it is Mexico City.

In 1428 they joined two other cities in the Triple Alliance and built a tribute empire over central Mexico. Conquered peoples had to send them goods, much as defeated kings in Indian history paid tribute to an emperor. The Basin of Mexico held 1–2 million people.

In 1521, the Spanish conqueror Hernán Cortés took Tenochtitlan. He had the help of thousands of local allies, the Tlaxcalans, and of smallpox, a deadly disease. The conquered land became “New Spain”.

Ethnohistory studies peoples who left few written records of their own, such as the Aztecs, by combining documents with anthropology. Its documents were written after the conquest by Spanish friars or by native scribes. Two famous ones are the Codex Mendoza, from about 1541, and the Florentine Codex, put together by Bernardino de Sahagún in the 1570s.

At birth, an Aztec girl was given spinning and weaving tools as a symbol, and a boy was given a shield and arrows. Making maize tortillas took hours of grinding every day, much like grinding grain on a stone hand-mill, the chakki, in an old Indian village home.

Picture Germany in the 19th century. There, Leopold von Ranke founded modern history based on sources. He insisted on primary sources, records made at the time and kept in archives. He also insisted on critical editions of them, checked and printed with notes. He invented the research seminar and famously aimed to show the past “wie es eigentlich gewesen”, “as it actually was”.

Then history became a profession. Johns Hopkins started a PhD programme in 1876, journals appeared, and the American Historical Association was founded in 1884. E. A. Freeman gave the age its motto, displayed at Johns Hopkins: “History is past politics”. That meant states, wars, diplomacy and constitutions, all male, public spheres, like an old school textbook full of kings and battles.

Before this, many amateur women writers, not trained as historians, had written popular histories and life stories. One example is Agnes Strickland’s Lives of the Queens of England, from the 1840s. Now such books were dismissed as unscientific, and universities rarely hired women.

Eleanor Roosevelt was born in 1884, the niece of President Theodore Roosevelt. In 1905 she married a distant cousin, Franklin Delano Roosevelt, known as FDR. He was President from 1933 to 1945 and was elected four times. He led the country through the Great Depression and World War II, and he died in office in April 1945.

Eleanor was busy long before the White House. As a young woman she worked in a settlement house, a centre in a poor neighbourhood where middle-class reformers lived and offered help. In 1921 FDR was paralysed by polio. Through the 1920s Eleanor was active in the League of Women Voters, the Women’s Trade Union League and the women’s division of the New York Democratic Party. She also taught school, and she became his political “eyes and ears”.

In 1933 she became First Lady, the President’s wife. She held press conferences for women reporters only, so newspapers had to employ some women. She wrote a daily column, “My Day”, a bit like a public diary. She pushed for civil rights, young people and workers, often ahead of FDR. In 1939 the Daughters of the American Revolution barred the Black singer Marian Anderson from its hall, and Eleanor resigned from the group.

After 1945 she kept working. As a US delegate to the United Nations, she chaired the Human Rights Commission. It drafted the Universal Declaration of Human Rights in 1948, a statement of the basic rights every person should have. Then, in 1961–62, she chaired President John F. Kennedy’s Commission on the Status of Women.

Women’s history itself moved through stages. Early work celebrated exceptional “great women”. Later, social history, the history of ordinary people, asked what made a woman typical of a group or generation.

In America, Eleanor Roosevelt is a household name. In her lifetime she topped Gallup’s poll of the “most admired woman” year after year. FDR’s New Deal, his 1930s programmes of relief, recovery and reform, is a core part of what American students learn.

Puritans, strict English Christians, founded the colony of Connecticut, starting with Hartford in 1636. In 1639 the settlers wrote down their rules in the Fundamental Orders, often called the first written constitution in America. Dayton’s book starts there and ends in 1789, the year the US Constitution took effect.

A civil case is a private dispute over a debt, a contract or property. In a criminal case, the state prosecutes an offence. Foundation 2 explains more.

Coins were scarce in the colonies, so trade ran on credit. Shopkeepers kept book debts, running accounts in a ledger, much like the khata at an Indian kirana shop. Neighbours also swapped IOUs, short notes that say “I owe you”. So suing a neighbour for debt was routine, not hostile.

A promissory note was a written promise to pay. Such notes were negotiable: the holder could sign one over or sell it to someone else, much as you can endorse a cheque. So credit became impersonal, and it could stretch to distant merchants. It was part of two bigger 18th-century changes: a more commercial Atlantic economy and the rise of professional lawyers.

Marriage decided whether a woman could sue in her own name. A single woman or a widow, a feme sole, could. A married woman, a feme covert, lived under coverture, which merged her legal identity into her husband’s. So she generally could not sue, except as her husband’s agent. The historian Laurel Thatcher Ulrich called such wives “deputy husbands”.

World War I began in Europe in August 1914. The US stayed neutral until 6 April 1917, when it declared war, about two months after the New York boycott. In between, the US sold vast amounts of food and munitions to Britain and France, and that helped push up prices at home. Indians know this logic from onions: when large amounts go abroad, prices in the local market rise.

The Socialist Party of America was founded in 1901. Its leader, Eugene V. Debs, won about 6% of the vote for President in 1912. The party was strong among Jewish immigrant garment workers on New York’s Lower East Side. That district even sent a Socialist, Meyer London, to Congress.

The party opposed entering the war, and it was then repressed. In 1918 Debs was convicted under the wartime Espionage Act for an anti-war speech. The Red Scare of 1919–20, a wave of fear of radicals, followed.

The point of production is the workplace, with its strikes and unions. The point of consumption is the shop, where people buy. Marxists saw the workplace, along with elections, as the real arenas of class struggle, the fight between workers and owners. Housewives’ protests as shoppers, such as boycotts and rent strikes, looked secondary to them. That explains the Socialists’ “basic indifference”.

New York housewives had protested like this before. In 1902 Jewish housewives on the Lower East Side boycotted kosher meat, meat prepared under Jewish religious law, much as halal meat is under Muslim law. In 1907–08 came rent strikes, when tenants refused to pay rent. Later in 1917, in November, New York women won the vote in state elections. That was three years before the 19th Amendment gave women the vote nationwide.

The Quakers, or Religious Society of Friends, were founded by George Fox in England in the 1650s. They believe in an “Inner Light” in every person. If everyone carries the same light, then women and men are spiritually equal. So Quaker women could preach, and they ran their own “women’s meetings”. Quakers were also pacifists, who refused to fight in wars, and they were among the first anti-slavery activists.

In 1681 the Quaker William Penn founded Pennsylvania as a “holy experiment” in religious tolerance. Its main city, Philadelphia, was founded in 1682 and nicknamed the “City of Brotherly Love”. By the 1770s it was the largest city in British North America. Like Mumbai today, it was very mixed. Quakers lived beside Anglicans, German sects, Scots-Irish Presbyterians, and free and enslaved Africans.

Quakers wanted both girls and boys to be literate. Their schools kept free “charity” places for poor children and for children who were not Quakers. The Quaker teacher Anthony Benezet, for example, ran schools for girls and for Black children.

Many readers of the 1600s and 1700s kept a commonplace book, a personal notebook for copying out favourite poems, quotations and recipes. Poems also passed among friends in handwritten copies, much as people forward a good poem on their phones today.

Under coverture, marriage ended a woman’s separate legal identity. A single woman or a widow, a feme sole, kept hers. That is why the large group of never-married and widowed women, the women who were “not all wives”, interests historians.

In colonial schools, reading was taught before writing. Many colonial women could read but not write. So “literacy competence” was a real barrier.

Picture Florence in the 1400s. The Strozzi are a rich banking family, but in 1434 the powerful Medici exile them. Alessandra Macinghi Strozzi, born about 1407, is widowed young, in the 1430s. She stays in Florence while her sons live in exile, in Naples and Bruges.

About 70 of her letters to them survive. They are a famous source on Renaissance family life: arranging marriages, managing property and lobbying to end the exile. The exile was lifted in 1466, and her son Filippo later built the grand Palazzo Strozzi.

Florentine families of the time were patrilineal: they traced the family line through men. The male line, the family’s honour, dowries and arranged marriages counted for more than any one person’s wishes. A woman even needed a male legal guardian to make a contract.

Historians look for the “individual” because in 1860 Jacob Burckhardt claimed that the Renaissance discovered it (see p.23). The anthropologist Clifford Geertz famously called the Western idea of a “bounded, unique” self “a rather peculiar idea within the context of the world’s cultures”. Cultural psychologists contrast two kinds of self. The independent self, common in the US, stands on its own. The interdependent self, common in East Asia and South Asia, is defined by its relationships.

McKim Marriott described South Asian persons as “dividuals”, a play on “individuals”. The Indian joint family is a good mental model here. In it you are always someone’s son or daughter, nephew or cousin, and your place in that web helps define who you are.

The Renaissance, meaning “rebirth”, ran from roughly 1350 to 1600. It revived Greek and Roman learning, a movement called humanism. Famous names include Leonardo, Michelangelo, Petrarch and Erasmus.

The Renaissance began in the Italian city-states, small states each run from a city, such as Florence, Venice and Rome. From there it spread north to England, in the age of Elizabeth I, who reigned 1558–1603, and of Shakespeare. Gutenberg’s printing press, from about 1450, helped it spread.

In 1860 the Swiss historian Jacob Burckhardt published The Civilization of the Renaissance in Italy. That book defined the Renaissance as the birth of the modern individual. His view of women was based on a few highly educated noblewomen of the Italian courts.

In 1977 Joan Kelly wrote the essay “Did Women Have a Renaissance?”, a founding text of women’s history. Her key point concerned periodization, the way we divide history into named eras. An age of “progress” for men, she said, may be one of loss for women. Think of the monsoon: the same rains that bless farmers can flood a city’s commuters.

In Kelly’s view, medieval courtly love, the ideal of a knight devoted to a noble lady, gave aristocratic women some autonomy. The Renaissance court, she argued, made the lady an ornament. Castiglione’s Book of the Courtier (1528) pictures that court.

The querelle des femmes, “the woman question”, was a debate about women’s nature and worth that lasted centuries. Christine de Pizan’s Book of the City of Ladies (1405) is the famous early defence.

The American Revolution began with fighting at Lexington and Concord in 1775. The Declaration of Independence came on 4 July 1776, America’s 15 August. The war ended with the Treaty of Paris in 1783, and the Constitution followed in 1787.

Republicanism, with a small r and no link to the Republican Party, was an 18th-century set of ideas drawn from ancient Rome. It held that a government without a king survives only if its citizens have civic virtue, putting the public good above private interest. Think of a cricket team that wins only if players bat for the side, not for their own records. In this view, luxury and corruption had destroyed Rome and could destroy America too. So raising virtuous children became a political task.

Linda Kerber named this idea republican motherhood. She developed it from the late 1970s into the 1980s, as in her 1980 book Women of the Republic. In this idea, women had no vote but a civic role at home, which justified educating them. Examples include Benjamin Rush’s 1787 Thoughts upon Female Education and Judith Sargent Murray’s 1790 essay “On the Equality of the Sexes”. Two schools are examples too: the Young Ladies’ Academy of Philadelphia, founded in 1787, and Litchfield Female Academy, in 1792.

An academy was a private, fee-paying school. Academies existed long before free public high schools spread after the 1830s, the time of Horace Mann’s movement for free, tax-funded common schools.

In APUSH, the Advanced Placement US History course, students memorise “Republican Motherhood” as a vocabulary term. They often pair it with Abigail Adams, who wrote “Remember the Ladies” in a 1776 letter.

The English Civil Wars ran from 1642 to 1651. On one side were the Royalists, nicknamed “Cavaliers”, who supported King Charles I. On the other were the Parliamentarians, nicknamed “Roundheads” and often Puritans, strict English Christians. They fought over taxes, religion and royal power.

Charles I was beheaded in 1649. England then became a republic under Oliver Cromwell. In 1660 the Restoration brought back a king, Charles II. Later, the Glorious Revolution of 1688 and the Bill of Rights of 1689 made England a constitutional monarchy, with the king’s power limited.

Robert Filmer’s book Patriarcha, published in 1680, argued that kings inherit Adam’s fatherly authority from God. This idea is called the divine right of kings.

John Locke replied in 1689 with Two Treatises of Government. The First Treatise attacks Filmer. The Second sets out natural rights and government by consent, ideas that later became the basis of the US Declaration of Independence. Yet Locke still accepted a husband’s rule in marriage as “natural”.

Mary Astell, who lived from 1666 to 1731, was a High-Church Tory in the Royalist tradition. Her best-known lines come from Some Reflections upon Marriage, published in 1700 and again in 1706. One asks: “If absolute Sovereignty be not necessary in a State, how comes it to be so in a Family?” Sovereignty means supreme power. The other asks: “If all Men are born free, how is it that all Women are born Slaves?” Astell is often called the first English feminist.

American textbooks usually date the Progressive Era to about 1890–1920. It was a reform response to industrialisation, growing cities, immigration and corruption. A broader definition runs from the Panic of 1893, a severe depression with mass unemployment, to US entry into World War II. For this reading, keep that broader span in mind.

Journalists called muckrakers exposed wrongdoing. Jacob Riis wrote How the Other Half Lives in 1890, and Upton Sinclair wrote The Jungle in 1906. Other reforms included food-safety laws, four amendments to the Constitution between 1913 and 1920, and Theodore Roosevelt’s trust-busting, the breaking up of giant companies.

Jane Addams ran Hull House, a settlement house in Chicago where reformers lived among poor immigrants and offered them services. Florence Kelley worked with the National Consumers League, from 1899, and the National Child Labor Committee, from 1904. Lewis Hine’s photos of child workers in mills and mines shocked the public. Many states let women vote in school-board elections long before 1920, because schooling was seen as women’s sphere.

In 1900 roughly 1 in 6 children aged 10 to 15 worked for pay. Congress passed a first ban in 1916, but it was struck down in the 1918 case Hammer v. Dagenhart. The Fair Labor Standards Act of 1938 finally prevailed.

In industrial home work, families in crowded tenements finished garments, made artificial flowers or rolled cigars at home. They were paid by the piece, and children helped. In the family wage economy, picture one pot on the kitchen shelf that every member’s earnings go into. In poor households, children’s earnings were a vital share of that pot.

Americans learn the Progressive Era as a major reform period. They usually meet it through the muckrakers, Theodore Roosevelt and Jane Addams.

Two revolutions remade Britain. The Agricultural Revolution, about 1700–1850, brought enclosure: open fields and commons were fenced off as private land. It also brought new crop rotations, selective livestock breeding and larger commercial farms. Wage labourers replaced small family farmers, and the extra food fed the growing industrial cities.

The Industrial Revolution, about 1760–1840, brought textile machines, Watt’s steam engine, factories and, from 1830, railways. It moved production out of the home and into the factory.

Farmhouse cheeses such as Cheddar, Cheshire, Stilton and Gloucester were traditionally made by farmers’ wives and dairymaids. It was skilled, heavy work. Factory cheese-making, copied from New York State, reached England around 1870.

Early women’s historians, Alice Clark in 1919 and Pinchbeck in 1930, told a story of decline. Before industry, they said, wives were working partners in a “family economy”, and capitalism ended it. Later historians, such as Judith Bennett, stressed continuity: women’s work was low-status both before and after.

Picture California in 1769. Spanish missions began there under the friar Junípero Serra, and in time there were 21 of them. Spain also built presidios, or forts, and pueblos, or towns. Los Angeles began as a pueblo in 1781.

Mexico won independence from Spain in 1821, so California became a Mexican territory. In the 1830s the mission lands were secularised, that is, taken out of church hands. They were granted as huge ranchos, or cattle ranches, to a Californio elite. These families traded cattle hides and tallow with ships from New England. Richard Henry Dana’s Two Years Before the Mast (1840) describes this world.

Some Anglo-American and British merchants settled there. They converted to Catholicism, became Mexican citizens and married daughters of elite Californio families. They gained land, status and connections.

In 1845 Americans spoke of Manifest Destiny, the belief that the US was destined to spread across the continent. The Mexican–American War came in 1846–48. In the Treaty of Guadalupe Hidalgo of 1848, the US gained California and the Southwest, roughly half of Mexico’s territory. Gold was found in 1848, the Gold Rush followed in 1849, and California became a state in 1850.

The treaty promised to respect property. But the Land Act of 1851 forced Californios to prove their land titles in costly lawsuits, and many lost their land.

Spain and Mexico used civil law, based on written codes, while England used common law, built up from judges’ past decisions. Under Hispanic law a married woman kept her own property and could inherit equally with her brothers. She also shared community property with her husband, a bit like a joint bank account. Under common law, a rule called coverture passed a wife’s property to her husband. The Hispanic rule is why California, Texas, Arizona, New Mexico and some other states are still “community property” states.

The new political history was part of a broader “new social history”, history written from the bottom up. It used computers and statistics, such as vote tallies and census data, to study how masses of people voted. It found that religion and ethnicity strongly predicted 19th-century voting.

Men’s politics in the 1800s was intensely partisan, that is, loyal to a party. There were parades, party newspapers and patronage jobs given to loyal supporters. Voter turnout was often above 75%. Think of election season in an Indian town, with rallies and party flags everywhere.

Petitions were one part of women’s public life before the vote. Petitioning is a right protected by the First Amendment. Voluntary associations were another part. The largest women’s group of the century was the Woman’s Christian Temperance Union, founded in 1874. Temperance meant the campaign against alcohol.

Tsarist Russia was an autocracy, an absolute monarchy under the Romanov tsars. Serfdom, which bound peasants to their lords’ land, was abolished only in 1861. Most Russians were peasants, and industry came late, from the 1890s. So Russia looked “backward” next to Western Europe.

In 1905, after “Bloody Sunday”, mass strikes forced Tsar Nicholas II to create an elected parliament, the Duma. But women could not vote for it. That spurred women to organise, for example in the Union for Women’s Equality, founded in 1905. In 1908 about 1,000 delegates met at a women’s congress in St Petersburg. There, socialist women organised by Alexandra Kollontai clashed with the liberal majority.

Marxists had their own view of “the woman question”. In this view, women’s oppression came from private property and from the family as an economic unit. Engels set this out in The Origin of the Family, Private Property and the State (1884). So, Marxists said, socialism would free women automatically. They condemned cross-class “women’s” alliances for dividing the working class.

In February 1917, on International Women’s Day, women textile workers went on strike over bread shortages. The revolution began, and the Tsar abdicated. The new Provisional Government gave women the vote that year. In October the Bolsheviks, led by Lenin, took power. Kollontai became People’s Commissar for Social Welfare, one of the first women anywhere to hold a cabinet post.

Americans learn about 1917 and the Cold War, but rarely about these movements. The “bourgeois” goals resemble the individualist strand of feminism (compare p.8).

Under the Joseon dynasty, from 1392 to 1910, Korea made Neo-Confucianism its state ideology. It stressed filial piety, a child’s duty to honour parents, along with hierarchy, the patrilineal family and ancestor rites. Women owed the “three obediences”, to father, husband and son. Korea’s male-headed family registry, the hoju, was ruled unconstitutional in 2005.

In 1886 Mary Scranton, an American Methodist missionary, founded Ewha as Korea’s first modern school for women. Today it is Ewha Womans University, its official spelling, and one of the world’s largest women’s universities.

Picture Korea in 1977. It had been divided in 1945 at the 38th parallel, with a Soviet-backed North and a US-backed South. The Korean War of 1950–53 ended in an armistice, a ceasefire, not a peace treaty. So “national unification” was a sacred goal.

In the South, the authoritarian Park Chung-hee held power from 1961 to 1979. He drove rapid industrialisation based on exports, the “Miracle on the Han River”. It relied heavily on low-paid young women in textile and electronics factories. So, to critics, feminism looked like a “distraction”.

Freud, who lived from 1856 to 1939, founded psychoanalysis, a method of exploring the unconscious mind. His Oedipus complex is a son’s rivalry with his father for his mother. He also stressed rivalry between brothers and sisters. Western feminists such as Betty Friedan and Kate Millett attacked his sexism, for example his idea of “penis envy”. The Korean critique targets something else: his individualism and his assumption of the nuclear family.

A “Darwinian struggle” is competition for survival, as in “survival of the fittest”. Applied to a family, it turns family members into competitors. Cultural psychologists contrast the independent self of the West with the interdependent self of East Asia. The Japanese psychiatrist Takeo Doi made a parallel argument in 1971 about amae, healthy dependence. Indian readers will recognise the logic of the joint family.

Picture a dry valley in the American West, with one river and many thirsty farms. The West shares out such water by a rule called prior appropriation: “first in time, first in right”. Whoever first put the water to use holds the senior right. In a drought, senior rights are served first, even if junior users get nothing.

It works like a queue at a ration shop: when stock runs out, those at the back go home empty-handed. So in the West, a water right’s date, its priority date, is crucial. A priority date of 1848 puts its holder ahead of almost all later settlers. The wetter East is different: there, under riparian rights, landowners along a stream share its water.

In 1888 the Fort Belknap Reservation was created in Montana. It is home to the Gros Ventre and Assiniboine tribes. Upstream, settlers had diverted the Milk River, and the quarrel led to the Winters case of 1908. From it comes the reserved-rights doctrine: land that the federal government sets aside silently comes with enough water for its purpose. This holds for a reservation, a national park or a military base, and the water’s priority date is the date of the reservation.

Far to the south, along the Rio Grande in New Mexico, live the peoples called pueblos. The Spanish named them after their compact adobe towns, built of sun-dried mud brick. They farmed with irrigation long before Spain arrived, and they held Spanish land grants. In 1848 the Treaty of Guadalupe Hidalgo ended a war with Mexico, and the United States gained New Mexico.

In US law, the pueblos’ position was truly unclear. In US v. Joseph (1876), the Supreme Court said they were not an “Indian tribe” under one federal law. Then US v. Sandoval (1913) reversed course and placed them under federal guardianship.

Arizona v. California (1963) was a long fight over Colorado River water. It also confirmed reserved rights for five tribes, including reservations created by executive order of the President rather than by treaty. Colorado River shortages are regular news, and Western Americans grow up with “water wars”. India has its own, such as the long Cauvery dispute between Karnataka and Tamil Nadu. As a Western saying goes, “Whiskey’s for drinking, water’s for fighting.”

Picture the US in 1900. Its Native population has fallen to its lowest point, about 250,000 people. The 1890 census has already declared the frontier, the moving edge of settlement, “closed”. This is the time of “the vanishing Indian”.

Believing these cultures were about to disappear, anthropologists rushed to record them. This is called salvage ethnography: like a salvage crew at a shipwreck, they saved what they could. Edward Curtis’s photographs, published from 1907 to 1930, came from the same impulse.

Ethnography is the detailed description of one culture, based on fieldwork. Ethnology compares many cultures. In the US, anthropology has four fields: cultural, linguistic, archaeological and biological.

Franz Boas, a German-born professor at Columbia, is known as the “father of American anthropology”. He championed cultural relativism, the idea that each culture should be understood on its own terms, and he fought scientific racism. His students included Margaret Mead, Ruth Benedict, Zora Neale Hurston and Paul Radin. Ironically, Radin himself published a famous Native autobiography, Crashing Thunder (1926), the story of a Winnebago, or Ho-Chunk, man.

Some life stories were “as-told-to”: a Native narrator spoke, and a white editor wrote the story down. In Black Elk Speaks (1932), John Neihardt wrote down the life of a Lakota holy man, and people still debate how much he shaped it. Many Native cultures also avoid speaking the names of the dead. A ban like this, set by custom, is a taboo. In India, too, some traditional wives avoid saying their husband’s name.

As Foundation 2 explains, the President makes treaties “with the Advice and Consent of the Senate”, which takes a two-thirds vote. The House, the lower chamber of Congress, has no role. Yet Indian treaties committed federal money, and spending bills start in the House, much as money bills in India start in the Lok Sabha.

In 1867 the Medicine Lodge Treaty with the Kiowa, Comanche and Apache, in Indian Territory, now Oklahoma, set a rule. No reservation land could be ceded, or handed over, without the consent of three-fourths of the adult men.

The House resented being left out of treaties. In 1871 it attached a rider, an extra clause, to that year’s Indian Appropriations Act, a spending law. No tribe would again be recognised as a nation “with whom the United States may contract by treaty”. Existing treaties stayed valid.

This was the era of the Dawes Act and allotment. Reservations were divided into family plots, and the “surplus” was opened to whites. For the Kiowa, Comanche and Apache, an allotment agreement of 1892 lacked valid consent. Congress enacted it anyway in 1900, and in 1901 their lands were opened by lottery.

Kiowa leader Lone Wolf sued the Interior Secretary, Ethan A. Hitchcock. In 1903 the Supreme Court ruled that Congress has plenary power over Indian affairs and may override treaty terms on its own. Courts will not second-guess Congress, presuming that it acts in “perfect good faith”. Scholars sometimes call the ruling the “Indians’ Dred Scott decision”, after the case that said Black people could not be citizens.

In 1994 Blue Clark, a Muscogee (Creek) historian, published a book on the case.

Picture a map drawn on birchbark or deerskin, or traced in sand or snow. Native peoples made such maps and gave some sketches to Europeans. In the 1720s, colonial officials received a Catawba map on deerskin. Like a metro map, these often showed relationships and routes, not surveyed boundaries.

Ideas about land differed too. Native systems of land tenure, the rules for holding land, were often communal, shared by the whole group. Or they rested on use, such as rights to hunt, fish or farm. Europeans pictured absolute ownership of a plot with fixed edges. So a Native “territory” is hard to map.

In government hands, maps were tools of power. Treaty maps marked land that tribes had ceded, or given up. The federal survey grid of the 1785 Land Ordinance cut land into square-mile “sections”. It turned Native homelands into property for sale.

With trust land, the federal government holds the legal title “in trust” for a tribe or an individual Indian. Such land can’t be freely sold, and states generally can’t tax it. This follows from the trust relationship, a federal duty to protect tribes, set by the Marshall Court (see Foundation 3). In India, too, many states limit the sale of tribal land to non-tribal buyers.

In 1824 the US set up the Bureau of Indian Affairs, or BIA. It ran reservations, schools, leases and allotments, plots carved out of reservations for individual Indians. Critics have long called it paternalistic, meaning it treats adults like children. Since the 1970s, its staff have been mainly Native people.

Picture a traditional American history textbook. Columbus “discovered” America. Settlers tamed a “wilderness” or “virgin land”. In 1893 the historian Frederick Jackson Turner described the frontier as the line between “savagery and civilization”. There is Manifest Destiny, the belief that the US was meant to spread across the continent. And there are the Pilgrims, sharing a friendly Thanksgiving in 1621.

Here is what that story left out. Near today’s St Louis stood Cahokia, a city of perhaps 10,000–20,000 people between about 1050 and 1350, with huge earthen mounds. Ancestral Puebloan people built cliff cities at Mesa Verde. The Hohokam dug irrigation canals. Native farmers grew the “Three Sisters” together: maize, beans and squash. And the Haudenosaunee, or Iroquois, Confederacy, a league of Native nations, lived by its Great Law of Peace. In 1988 Congress formally recognised its influence on the US system of government, though historians debate how much.

Scholars have names for two ways of seeing another culture. Ethnocentrism, a term W. G. Sumner wrote about in 1906, means judging it by your own culture’s standards. Its opposite, cultural relativism, is linked to the anthropologist Boas. It means understanding a culture on its own terms.

In 1995 James Loewen’s bestseller Lies My Teacher Told Me attacked exactly these biases in textbooks. Native mascots, the symbols that sports teams use, were contested too. In 2020–22, Washington’s American football team and Cleveland’s baseball team dropped their Native names.

Americans grow up with Columbus Day, now often renamed Indigenous Peoples’ Day. Children act in Thanksgiving pageants, school plays about that friendly feast. And “textbook wars” over how history is taught break out again and again. India has its own arguments over what school history books should say.

Picture Norse Vikings reaching Newfoundland, an island off the east coast of Canada, about 1000 CE. They landed at a place now called L’Anse aux Meadows. Historians call the years from about 1500 to 1800 the early modern era. So that label leaves out the much earlier Viking contact.

In 1497 John Cabot sailed to Newfoundland, a year before Vasco da Gama reached India. Its fishing grounds, the Grand Banks, were one of the world’s richest cod fisheries. After Cabot’s voyage, Basque, Portuguese, French and English crews came every summer. Many landed to dry and salt their cod on shore, much as fishing families on the coasts of India dry fish in the sun. That brought them into contact with the Beothuk and Mi’kmaq peoples. Fishermen kept few written records.

In 1501 the Portuguese Corte-Real voyages explored Newfoundland and seized Native captives. Reports from Lisbon noted that the captives already had European-made objects. Later, in 1534–35, the French explorer Jacques Cartier explored the Gulf of St Lawrence and claimed it for France.

Why furs? Europe had a craze for hats made of felt, a thick cloth of pressed fibres, and this felt came from beaver fur. The fur trade powered French Canada, where Quebec was founded in 1608. It also powered Dutch New Netherland and the Hudson’s Bay Company, set up in 1670. And it reshaped Native economies and wars, as in the “Beaver Wars” of the 1600s.

Native peoples valued metal goods highly, such as iron tools and copper kettles, which they cut into ornaments. Nicolas Denys was a French colonist and merchant in Acadia, now Nova Scotia.

Picture three mesas, flat-topped ridges shaped like giant tables, in north-eastern Arizona. On top sit the villages of the Hopi, a Pueblo people. One village, Old Oraibi, has been lived in since about 1100 CE. It is among the oldest continuously occupied towns in the US.

Hopi clans are matrilineal: you belong to your mother’s clan. Houses and fields pass down the female line, and a husband joins his wife’s household. The Khasi of Meghalaya, in north-east India, follow a similar pattern. Clans also “own” particular ceremonies and ritual knowledge, such as katsina rituals and the Snake Dance.

In 1680 the Pueblo peoples rose up. In this Pueblo Revolt, led by Popé, they drove the Spanish out of New Mexico for 12 years. The remote Hopi killed their missionaries. Unlike the pueblos on the Rio Grande, they were never brought back under Spanish rule.

The Hopi also faced other pressures. Droughts and smallpox epidemics struck, notably in the late 1700s. Navajo and Ute raiders attacked. And there was contact with Spanish and Mexican outsiders.

Around 1880, US influence grew stronger. In 1882 an executive order, a direct order from the president, created a Hopi reservation. Railways and government schools arrived too. Today the Hopi Reservation is surrounded by the much larger Navajo Nation.

Picture the Inca Empire, also called Tawantinsuyu. From its capital, Cusco in Peru, it grew fast between about 1438 and 1533. It reached roughly 10 million people, the largest state in the Americas before the European conquest.

Its road network stretched 40,000 km, about the distance around the Earth. It recorded data on quipus, knotted cords, instead of writing. Machu Picchu dates from about 1450. In 1532–33, Pizarro conquered the empire.

The land rose through several altitude zones. Along the coast lay desert, while warm valleys grew maize, cotton, chili, coca and fruit. Temperate slopes grew maize. On the puna, the high cold grassland, people grew potatoes and quinoa and herded llamas and alpacas. Potatoes were freeze-dried into chuño so they would keep.

For scale, 9,000 feet is about 2,750 metres, higher than Shimla. And 3,000 feet is about 900 metres, roughly the height of Bengaluru.

In 1972 the anthropologist John Murra gave a name to an Andean pattern: the vertical archipelago. An archipelago is a group of islands. Under this pattern, one group’s fields and herds were scattered across several altitude zones, like islands in a sea.

Picture the cold subarctic forests of Canada, just south of the Arctic. Here the Cree, Innu (or Montagnais) and Ojibwe (or Anishinaabe) hunt beaver, moose and caribou. Scholars study family hunting territories mainly among these forest peoples.

“Algonquian” is not one tribe but a language family, like the family that links Tamil and Telugu. Besides the Cree, Innu and Ojibwe, it includes the Mi’kmaq, Lenape, Powhatan, Wampanoag, Cheyenne and others.

The English thinker John Locke said property comes from mixing your labour with land, by farming it and enclosing it, or fencing it in. Colonists used his idea to argue that hunting peoples did not truly “own” land. To them, it was “vacant land”. So the question of Native property rights has always carried political weight.

In 1915 Frank Speck argued that family territories were aboriginal private property, meaning they existed before Europeans arrived. He did so partly to fight the claim that Native people lacked property and so could be dispossessed, or pushed off their land. In 1954 Eleanor Leacock disagreed. She said they arose after contact with Europeans. In her view, trapping furs for sale encouraged each family to keep its own trapping grounds.

In the 1970s–80s, fieldwork, or on-the-spot research, among the James Bay Cree found a layered system centred on the community. It was tied to land-claims talks over a giant hydro-electric project in Quebec. Cree belief also has give-and-take with animals: they “give themselves” to hunters who show them respect. A steward, called a tallyman, manages each territory for the group and must share.

Picture the Four Corners region of the American Southwest. Here the Ancestral Puebloans built the great houses of Chaco Canyon, in about 850–1150 CE, and the cliff dwellings of Mesa Verde in the 1200s. Their older name, “Anasazi”, is now avoided.

After a great drought in the late 1200s, people left the Four Corners and gathered in large villages to the south and east. The Western Pueblos, such as the Hopi, Zuni and Acoma, grew in the 1300s–1400s. A kiva is a ceremonial room, fully or partly underground. A Great Kiva is a large one for the whole community.

Why do archaeologists debate hierarchy, a ranking of people from top to bottom? Historic and modern Pueblo societies are often called egalitarian, treating people as equals, and run by consensus, or general agreement. So evidence of past chiefs or elites is controversial.

With no written records, archaeologists use clues: settlement size, storage space, imported goods and craft specialisation, where certain people focus on one craft. They also use burial analysis, comparing the objects buried with different people, called grave goods.

Farming comes in two kinds. Intensive farming puts more labour into each acre, through irrigation, terraces and check dams, low walls that slow running water. Extensive farming uses more land, with less labour on each acre.

Picture North America in the Pleistocene, the long age of repeated ice ages. It lasted from about 2.6 million to 11,700 years ago, and our own age, the Holocene, followed it (see Foundation 6). Woolly mammoths, mastodons, giant ground sloths, sabre-toothed cats, dire wolves, native horses and camels, and giant beavers lived here. Such large animals are called megafauna. North America lost about 35 genera of them, each genus a group of related species.

The earliest people in the Americas are called Paleo-Indians. Migrants reached the Americas by crossing Beringia, a land bridge between Asia and North America that appeared when sea levels fell. Clovis spear points, found with mammoth bones, are named after Clovis, New Mexico, much as the Harappan civilisation is named after Harappa. For a long time these points were thought to mark the first Americans, a view called “Clovis-first”.

Today, sites older than Clovis are widely accepted. They include Monte Verde in Chile, from about 14,500 years ago, and fossil footprints at White Sands, New Mexico, reported as about 21,000–23,000 years old. Older texts give “11,000 years ago” in radiocarbon years, the uncorrected result of carbon-14 dating. Calibrated, or converted, to calendar years, Clovis is about 13,000 years ago. So when sources quote different numbers, both are often right.

Paul S. Martin’s idea is called the overkill hypothesis, or “blitzkrieg”, meaning lightning war. He argued for it from the 1960s to 2005. He proposed that skilled hunters met animals with no fear of humans. The rival explanations are climate change, disease and a disputed comet impact. The climate change in question is a sudden cold spell called the Younger Dryas.

In 1999 Shepard Krech wrote The Ecological Indian. It challenged the romantic stereotype, or idealised picture, of Native Americans as natural conservationists, people who protect nature. Richard White is a leading historian of the American West.

Americans grew up with the “ecological Indian” image, as in the famous 1971 “Crying Indian” TV advert against litter. That is why this debate stirs strong political feelings in the US.

A 1908 play gave Americans the image of the “melting pot”: assimilation, with every group melting into one American identity. The rival image is the “salad bowl”, or multiculturalism, where groups keep their distinct identities.

Primordialism, linked to Edward Shils and Clifford Geertz, sees ethnicity as a deep attachment you are born into, rooted in blood, language, religion and custom. Instrumentalism, linked to the 1963 book Beyond the Melting Pot by Glazer and Moynihan, says ethnic groups act as interest groups competing for resources.

In 1969 Fredrik Barth offered a third idea, constructivism: ethnic identity is made and remade at the boundaries between groups. The “process” view of ethnicity is close to this.

The 1950s Relocation programme moved many Native people to cities. There, members of different tribes forged a shared “American Indian” political identity. This is pan-Indian identity, where “pan” means “all”, as in “pan-India”. Examples include the National Congress of American Indians, from 1944, and the American Indian Movement, from 1968.

The civil rights movement of 1954–68 inspired Red Power, the Native American movement, and also the Chicano, Asian American and women’s movements (see Foundation 1). Native activists occupied Alcatraz, a former prison island, in 1969–71. In 1972 they seized the headquarters of the BIA, the government office for Indian affairs.

From 1960 to 1990, the number of Americans calling themselves Native in the census grew far faster than births could explain. Sociologist Joane Nagel called this “ethnic renewal”, a textbook case of ethnicity as a process.

Between 1910 and 1970, about 6 million Black Americans left the South. This was the Great Migration. They moved to Chicago, Detroit, New York’s Harlem, Philadelphia and Cleveland, and later to the West Coast. Popular retellings include Isabel Wilkerson’s book The Warmth of Other Suns and Jacob Lawrence’s Migration Series paintings.

Push factors drive people out of a place, and pull factors draw them to a new one. The South’s push factors included Jim Crow, lynching, the loss of the vote, sharecropping debt, the boll weevil and floods.

A sharecropping family owned no land, farmed a landowner’s fields for a share of the crop, and was often trapped in debt. The boll weevil is a beetle from Mexico whose larvae destroy cotton bolls, the pods that hold the fibre. It spread from Texas across the Cotton Belt, the South’s cotton country, over several decades. Indian farmers know a similar pest, the pink bollworm.

The pull came from the North. World War I cut immigration from Europe from over a million a year to a trickle, and laws in the 1920s restricted it further. So Northern factories in steel, meatpacking and cars needed workers. Wages were higher, and Black people could vote.

The Chicago Defender, a Black newspaper founded in 1905, openly urged migration. Pullman porters, the Black attendants on overnight sleeping-car trains, often smuggled it south (see p.49). Northern labour recruiters also travelled south.

Start with a name. “Jim Crow” began in the 1830s as a character in blackface minstrel shows, where white performers darkened their faces to mock Black people. Later the name came to mean the whole system of segregation laws and customs, from about 1877 to 1965. It meant separate schools, rail cars and water fountains, poll taxes and literacy tests, and lynching.

Before Jim Crow came Reconstruction (1865–77). Under the 13th, 14th and 15th Amendments, Black men voted, and around 2,000 held office, including US senators. After federal troops withdrew in 1877, white Southern leaders called “Redeemers” took back control.

The “prevailing dogma” said that segregation was a timeless Southern “folkway”, a custom that no law could change. W. G. Sumner summed it up: “stateways cannot change folkways”.

Woodward’s thesis, or main claim, was that race relations had been more fluid, or less fixed, in the 1870s and 1880s. In his account, rigid segregation laws came mainly in the 1890s and 1900s. If segregation was recent and man-made, it could be unmade. Later historians debated this “Woodward thesis”.

In May 1954, in Brown v. Board of Education, the Supreme Court overturned “separate but equal” in schools. Every judge agreed. Thurgood Marshall argued the case for the NAACP, and historians helped research what the people who wrote the 14th Amendment had intended. Virginia, where Woodward lectured, would soon lead “Massive Resistance” against desegregation.

In January 1776, Thomas Paine’s best-selling pamphlet Common Sense rallied the colonists to independence, before the Declaration of Independence. Hence Woodward’s joke that his first edition was like “a history of the American Revolution published in 1776”. He was writing while the civil rights revolution was still unfolding, like a cricket match report written during the first innings. Martin Luther King Jr. cited Woodward’s account of how segregation was created, most notably in his 1965 speech at the end of the Selma-to-Montgomery march.

W. E. B. Du Bois (1868–1963) was a sociologist. In 1895 he became the first Black American to earn a Harvard PhD. His 1903 book The Souls of Black Folk introduced “double consciousness”, the sense of always seeing yourself through others’ eyes. It declared that “the problem of the twentieth century is the problem of the color-line”, and one chapter criticised Booker T. Washington.

Du Bois co-founded the Niagara Movement in 1905 and the NAACP in 1909. He edited its magazine, The Crisis, and his editorial “Close Ranks” appeared there in July 1918. To “close ranks” is to stand closer together, like soldiers in a line.

Washington (1856–1915) was born enslaved, and in 1881 he founded a school, the Tuskegee Institute. His 1895 speech at the Atlanta Exposition, a large fair, became known as the “Atlanta Compromise”. It asked Black Southerners to focus on vocational education, or training for a trade, and on economic self-help. It also asked them to put off the fight over segregation and voting.

In the speech he said: “In all things that are purely social we can be as separate as the fingers, yet one as the hand…”. Washington’s network, the “Tuskegee Machine”, controlled funding and patronage, meaning jobs and favours handed out to supporters. It also quietly influenced Black newspapers or subsidised them, paying some of their costs.

William Monroe Trotter, a Harvard graduate, was Washington’s fiercest critic. From 1901 he edited the Boston Guardian. In 1903 he confronted Washington at a meeting, and he was jailed after this “Boston Riot”.

The US entered World War I in 1917, and Black soldiers served in segregated units. Wartime laws, the Espionage Act of 1917 and the Sedition Act of 1918, were used against publications that disagreed with the government. After the war, in 1919, Du Bois wrote: “We return. We return from fighting. We return fighting.” Today every APUSH student, in the high-school AP US History course, writes the standard compare-and-contrast essay on Washington and Du Bois.

Picture an overnight train journey in America. Passengers slept in luxury sleeping cars run by the Pullman Company. From the 1860s the company hired Black men, many of them formerly enslaved, as porters. A porter was like the attendant who looks after passengers in an AC coach of an Indian overnight train.

Passengers often called the porters “George”, after the company’s owner, George Pullman. The work meant long hours, low pay and dependence on tips. Yet porters were respected, well-travelled figures in Black communities.

A. Philip Randolph (1889–1979), a Harlem socialist who edited The Messenger, organised the Brotherhood of Sleeping Car Porters in 1925. Later, in 1941, his threatened March on Washington pushed President Roosevelt to ban discrimination in defence industries. His pressure helped win Truman’s 1948 order to desegregate the military, that is, to stop keeping Black and white troops apart. He was also the senior organiser of the 1963 March on Washington, working with Bayard Rustin.

Union recognition means that an employer agrees to bargain with a union as the workers’ representative. It is the gateway to collective bargaining, where workers negotiate pay and conditions as one group. A company union is a “union” created and controlled by the employer to keep an independent union out. In the 1930s, national laws banned such unions and made recognition achievable: the Railway Labor Act amendments of 1934 and the Wagner Act of 1935.

Most craft unions in the AFL, a large alliance of unions, barred Black workers (see p.14 and p.51). Craft unions grouped skilled workers by trade. Randolph spent decades fighting racism inside the AFL, and later inside the AFL-CIO, formed when the AFL merged with another alliance, the CIO. Today Pullman porters and Randolph are staples of Black History Month lessons each February, often linked to the 1963 March on Washington.

Marcus Garvey founded the Universal Negro Improvement Association, or UNIA, in Jamaica in 1914. In 1916 he arrived in Harlem, in New York City, and built it up there. By the early 1920s it was the largest mass movement in Black American history up to that point.

Garvey preached racial pride: “Up, you mighty race!” He also preached economic self-reliance, much like India’s Swadeshi idea. He called for “Africa for the Africans” and a back-to-Africa scheme. He started the Black Star Line shipping company in 1919, founded the Negro World newspaper and gave his followers the red, black and green flag.

In 1923 he was convicted of mail fraud, cheating people through the post, and in 1927 he was deported. Still, he influenced Malcolm X, the Rastafarian faith, Black Power and Pan-Africanism, the idea of unity among people of African descent everywhere. He also feuded bitterly with Du Bois, another Black leader.

Back in World War I, about 380,000 Black soldiers had served, most in segregated labour units. The 369th Infantry, the “Harlem Hellfighters”, fought under French command and won the Croix de Guerre, a French medal for bravery. The veterans came home to the Red Summer of 1919, with race riots in dozens of cities. Some men still in uniform were lynched, killed by a mob without a trial.

Anthropologists study human cultures. In 1956 one of them, Anthony F. C. Wallace, published an article called “Revitalization Movements”. To revitalize is to give new life. His examples include the Seneca prophet Handsome Lake’s religion, the Ghost Dance of 1890 and Melanesian cargo cults.

Finally, there is the American success ethos, or guiding belief. It celebrates the self-made man, like the heroes of Horatio Alger’s rags-to-riches stories. Americans also call it the “American Dream”.

Picture the American South in the 1930s and 1940s, with its tobacco, steel, lumber, docks and meatpacking. Birmingham, Alabama, made steel, and R. J. Reynolds made tobacco goods in Winston-Salem.

There were two main groups of unions (see p.14). The AFL was craft-based, with one union per skilled trade, and often whites-only. The CIO was industrial, taking in all workers in an industry, and officially egalitarian, standing for equal rights. In 1943 workers at R. J. Reynolds formed a CIO local, or branch, that was heavily Black and female.

A union contract, the deal it strikes with an employer, could set up separate “Negro” and “white” job lines. Each line had its own seniority list, ranking workers by years of service. So Black workers could not transfer or be promoted into skilled, better-paid jobs. Title VII of the Civil Rights Act outlawed such arrangements in 1964.

The South was also hard ground for unions, with low wages and hostile employers. After the Taft–Hartley Act of 1947, “right-to-work” laws spread, letting workers stay out of unions. The CIO’s postwar drive to unionise the South, “Operation Dixie”, failed. Dixie is a nickname for the South.

On the American home front, meaning life back home during World War II, war production boomed and workers were scarce. This drew a second, larger wave of Black migration. In 1941, after Randolph threatened a march (see p.49), the president’s Executive Order 8802 banned discrimination in defence industries. A new Fair Employment Practice Committee was set up to enforce it.

In 1942 the Pittsburgh Courier newspaper launched the “Double V” campaign. Its two Vs stood for victory over fascism abroad and victory over racism at home.

Some white workers pushed back. In “hate strikes”, they walked out when Black workers were promoted. At Detroit’s Packard plant in 1943, about 25,000 struck, and the Detroit race riot of 1943 followed. In the Philadelphia transport strike of 1944, the army took over.

One reading of these years is the “lost opportunity” thesis. In 1988 Robert Korstad and Nelson Lichtenstein described what they called “civil rights unionism” in CIO unions led by the political left. They argued that postwar anti-communism killed it.

They pointed to two events. First, the Taft–Hartley Act of 1947 made union officers swear they were not communists. Then, in 1949–50, the CIO expelled left-led unions, among them the ones most committed to racial equality.

Herbert Hill was the labour director of the NAACP, a civil rights group. He is the best-known critic of unions’ record on race.

In the American Civil War, the Union, meaning the North, fought the Confederacy, the Southern slave states. About two-thirds of all deaths in the war came not from battle but from diseases such as dysentery, typhoid, malaria and pneumonia. At first, Black men were barred from the Union army. Then the Emancipation Proclamation, a declaration of freedom issued on 1 January 1863, allowed them to enlist.

About 179,000 Black men served in the United States Colored Troops, or USCT. That was roughly 10% of the Union army, and about 19,000 more served in the navy. Their officers were almost all white, much as Indian sepoys in the British Indian Army served under British officers.

Two episodes became famous. In 1863 the 54th Massachusetts regiment attacked Fort Wagner, an assault later dramatised in the 1989 film Glory. In 1864, at the Fort Pillow massacre, Confederates killed Black troops who were trying to surrender. The Confederacy also threatened to enslave or execute captured Black soldiers.

Pay was unequal too: a Black soldier got $10 a month, minus $3 for clothing. A white private, the lowest rank of soldier, got $13 a month plus clothing. In protest, the 54th Massachusetts refused any pay at all for 18 months. In 1864 Congress made the pay equal.

Armies also need labour. Fatigue duty meant digging trenches, building fortifications and guarding supply depots, and labour battalions did such work. The rear echelon means the area behind the front lines.

Americans meet this history at school. The film Glory is shown in many US classrooms, and the USCT is a standard textbook topic.

The Small Business Administration, or SBA, is a US government agency founded in 1953. It guarantees bank loans to small firms: if a firm cannot repay, the SBA pays the bank. It also gives advice, and through its “8(a)” programme it keeps a share of government contracts for disadvantaged firms.

In 1964 President Lyndon Johnson (LBJ) began a War on Poverty that included small-business loans. Then riots broke out in Watts in 1965 and in Detroit in 1967. In 1968 a government panel, the Kerner Commission, warned of “two societies, one black, one white—separate and unequal”.

Next, President Nixon promoted “Black capitalism”, which meant helping Black Americans own businesses. In 1969 his government set up the Office of Minority Business Enterprise.

Firms raise money in two basic ways. A loan is debt: it must be repaid with interest, whatever happens. Venture capital is equity: it buys a share of ownership, so the investor shares the risk and usually brings expertise and contacts. Think of the difference between a moneylender and a business partner.

Why do small firms fail? Some are undercapitalised, with too little start-up money. Others face weak markets, such as low-income neighbourhoods, or suffer from inexperienced management.

Picture San Francisco in 1968. Students at San Francisco State strike under the banner of the Third World Liberation Front. Their strike of 1968–69 is the longest student strike in US history. Students at UC Berkeley strike too.

The San Francisco strike created the first College of Ethnic Studies. Ethnic studies, the study of ethnic and racial groups in America, was born in these strikes. Asian American, Black, Chicano and Native American studies programmes followed across the country.

“Asian American” is a pan-ethnic umbrella, one label over many groups. It covers Chinese, Indian, Filipino, Vietnamese, Korean, Japanese and many other Americans, with very different histories, languages and religions. In the same way, the one word “Indian” covers people of many languages and faiths.

Three words from teaching are worth knowing. An anthology is one book that collects pieces by many different writers. A survey course is a broad introductory course. A reference work, such as an encyclopedia or a dictionary, is for looking up facts, not for reading straight through.

The Great Depression began with the US stock market crash of October 1929. It was at its worst in 1932–33. US output fell by about a quarter, unemployment hit about 25% and thousands of banks failed. World trade collapsed too, as the US raised import taxes with the Smoot–Hawley tariff of 1930 and other countries hit back.

Latin America lived on commodity exports, raw goods sold abroad. Brazil and Colombia sold coffee, Cuba sold sugar, Chile sold nitrates and copper, and Argentina sold beef and wheat. Then commodity prices crashed, and export earnings and government revenues collapsed.

Political upheaval followed. In 1930 a wave of revolutions and coups, sudden seizures of power, swept the region. Argentina had one, and in Brazil Getúlio Vargas took power. Populism, politics built on leaders who claim to speak for ordinary people, was on the rise.

Unable to afford imports, countries began making goods at home, such as textiles, processed food and cement. This is called import-substitution industrialisation, or ISI. Many historians therefore saw the Depression as a spur to Latin American industry. ISI later became official policy in the 1950s, linked with the economist Raúl Prebisch and the UN’s Economic Commission for Latin America.

Finally, keep two simple ideas in mind. Output is the quantity a firm produces, and profit is its revenue minus its costs. A firm can produce more while earning less, for example by cutting prices to keep its factories running. The reverse can happen too.

Figures reported to tax officials give owners a motive to under-report, which means to report less than the truth. This is a classic source of bias, a steady tilt in the numbers.

Picture a laboratory at MIT, a leading American university, in the 1970s. There, Richard Wurtman and John Fernstrom carried out classic research on food and the brain. Their work helped launch a whole new field, “nutrition and the brain”.

To follow their work, start with protein. Proteins are chains built from 20 kinds of small building blocks called amino acids, like necklaces strung from 20 kinds of beads. Nine amino acids are “essential”, which means the body cannot make them. Tryptophan is one of the nine, so the brain’s supply of it depends on diet.

The brain turns tryptophan into serotonin in steps. Tryptophan becomes 5-HTP, then serotonin, and serotonin can later become melatonin. The enzyme, or helper protein, that runs the first step normally works below full capacity. So when more tryptophan arrives, more serotonin is made, just as a half-busy factory makes more when more raw material comes in.

To reach the brain, tryptophan must pass through a transporter, a gate that it shares with the other “large neutral amino acids”. These are tyrosine, phenylalanine, leucine, isoleucine and valine. Picture several queues sharing one turnstile at a metro station. In most proteins, tryptophan is the scarcest of this group.

The pancreas releases insulin when carbohydrates raise blood sugar. Besides moving glucose into cells, insulin pushes many of the competing amino acids into muscle. Tryptophan, much of which rides in the blood on a protein called albumin, is less affected, so it faces less competition at the gate. This is the standard textbook account.

Many Americans “know” a piece of Thanksgiving folklore: the tryptophan in the holiday turkey makes you sleepy. Scientists call this a myth. Turkey has no more tryptophan than chicken, and in a protein-heavy meal the competing amino acids crowd tryptophan out. The drowsiness comes from the sheer size of the meal, much like the sleepiness after a big wedding lunch in India.

The longer you stay awake, the more adenosine builds up in your brain, and sleep clears it away. It is a by-product of using ATP, the cell’s energy molecule, and its build-up is called “sleep pressure”. Caffeine does not really give you energy. It hides the tiredness signal, like a strip of tape over a warning light on a car’s dashboard.

Caffeine belongs to a chemical family called the methylxanthines. Its relatives include theophylline, found in tea, and theobromine, found in chocolate. IBMX is a man-made methylxanthine used in laboratories.

Why did scientists need a new theory of caffeine? The older explanation said that caffeine blocks an enzyme inside cells, called phosphodiesterase. But that would take concentrations far higher than a coffee drinker’s brain reaches. Blocking receptors works at normal doses.

Pharmacology, the science of drugs, follows a standard logic. If a drug acts through a receptor, compounds that bind to it more tightly should generally act more strongly. So the key evidence is a correlation, a link between how well compounds bind and how strong their effect is. Later research found four kinds of adenosine receptor: A1, A2A, A2B and A3.

One drug can also do opposite things at different doses. Such effects are called biphasic, or dose-dependent. Alcohol is a familiar example: at low doses it is mildly stimulating, but at high doses it makes people sleepy.

Solomon Snyder of Johns Hopkins, a top American university, is one of the best-known American brain scientists. In 1973 he and Candace Pert discovered the brain’s opiate receptor. Coffee itself is central to American working life, from the office “coffee break” to Starbucks. The FDA, the US food and drug regulator, calls about 400 mg of caffeine a day, roughly four cups of brewed coffee, generally safe for healthy adults.

In 1950 Alan Turing proposed a simple test for machines, now called the Turing Test. Suppose you chat by typing with someone you cannot see. If you cannot tell whether a machine or a person is typing, you should call the machine intelligent.

In 1980 the philosopher John Searle offered a famous thought experiment, the Chinese Room. Picture a man who knows no Chinese, sitting in a room with a rulebook. Questions in Chinese come in through a slot, and by matching symbols to rules he passes out perfect Chinese answers. Outsiders think the room understands Chinese, yet nobody inside understands a word.

Searle’s moral is that running a program means following rules of form, or syntax, and that is never enough for understanding meaning, or semantics. So the Chinese Room aims to show that passing the Turing Test does not prove understanding. Searle’s target is “strong AI”, the claim that the right program literally is a mind. “Weak AI” says only that computers are useful tools for studying minds.

Searle’s favourite point is about simulation. A computer simulation of a rainstorm leaves nobody wet, and a simulated fire burns nothing. So, he argues, simulating a mind is not the same as having one.

Where does understanding come from, then? Searle holds that consciousness is a biological product of brains, just as photosynthesis is a product of plant cells. Brains, in his phrase, have “causal powers”. Critics complain that he never says which brain properties do the work.

The debate is alive again today. People argue over whether ChatGPT-style AI really “understands”, or merely predicts the next word, and that argument is a modern rerun of the Chinese Room. In America the Chinese Room is a staple of introductory college courses in philosophy and cognitive science. Films such as Her and Ex Machina have also made “can machines think?” a familiar American debate.

The word “circadian” comes from the Latin circa diem, “about a day”. Even in constant darkness, human rhythms keep running on their own, which is called “free-running”. But each cycle then lasts slightly longer than 24 hours, like a wall clock that runs a little slow.

Every day, cues called zeitgebers, German for “time-givers”, reset the rhythms. The main cue is light, but food and temperature count too.

The SCN is about 20,000 neurons. It sits just above the optic chiasm, where the two optic nerves cross, and that gives it its name: “supra-chiasmatic” means “above the crossing”. In the 1970s, rats whose SCNs were destroyed lost their daily rhythms. Later, transplanted SCN tissue restored rhythms in hamsters, and so the SCN earned the label “master clock”.

At night, on the SCN’s signal, the pineal gland releases melatonin, the “darkness hormone”. Around 2000–02, scientists identified light-sensing cells in the retina that contain a pigment called melanopsin. These cells don’t form images. They just tell the SCN how bright it is, which is why bright screens at night can disturb sleep.

In 2017 the Nobel Prize in Physiology or Medicine went to Jeffrey Hall, Michael Rosbash and Michael Young. They showed how clock genes, such as one called period, work in fruit flies. A protein builds up and then switches off its own gene, in a loop that takes about 24 hours. Think of the float valve in a rooftop water tank, which shuts off the inflow when the tank is full and opens again when the level falls.

Twice a year, Americans change their clocks for daylight saving time, unlike India, which keeps one clock time all year. Their rule of thumb is “spring forward, fall back”: clocks go forward in spring and back in the fall, the American word for autumn. In Congress, the American parliament, proposals to end the switch are often argued in body-clock terms. Melatonin is also sold over the counter in American pharmacies as a sleep aid.

In psychology, memory comes in several kinds. Declarative, or explicit, memory is what you can consciously put into words. In 1972 Endel Tulving split it in two. Episodic memory holds personal events, such as “my tenth birthday”, while semantic memory holds facts, such as “Delhi is India’s capital”.

Other kinds of memory work differently. Non-declarative, or implicit, memory covers skills such as riding a bike, along with habits and conditioning. You may not be able to explain how you balance on a bike, yet you still can. Working memory, or short-term memory, is also separate from long-term memory.

Tulving was born in Estonia and worked at the University of Toronto. He tied episodic memory to “autonoetic”, or self-knowing, consciousness: the feeling of re-living an event. He also tied it to “mental time travel”, which includes imagining the future. Recalling your tenth birthday can feel like stepping back into that day for a moment.

In 1953 surgeons removed much of the hippocampus of Henry Molaison, known as patient H.M. Afterwards he could no longer form new episodic memories. Yet he could still learn new motor skills, meaning physical skills. This was proof that memory has separate systems.

Crows, ravens, jays and magpies belong to a family called the corvids, which are among the most intelligent birds. Some nutcrackers hide thousands of seeds and find them months later. Scrub jays even re-hide their food if another jay watched them hide it. In 1998 Clayton and Dickinson published their scrub-jay “what-where-when” experiment in the journal Nature.

Intro psychology is one of the courses American college students take most often. So “episodic” and “semantic” memory, and the case of H.M., are familiar to many American readers.

Mass is the amount of matter in an object, measured in kilograms. Weight is the pull of gravity on that mass. A shopkeeper’s two-pan balance compares weights, since gravity pulls down on both pans. So when everything floats, the balance is useless.

Astronauts look “weightless”, but the word is misleading. At the height of the space station, gravity is still about 90 per cent as strong as on the ground. Astronauts float because they and their ship are in free fall, falling around Earth together. You get a brief taste of this feeling when a lift suddenly drops or a fairground ride plunges.

Anything moving in a circle needs an inward pull, called centripetal force. For a ball whirled on a string, the pull is the string’s tension. For stars or planets in orbit, the pull is gravity. More mass or more speed needs a stronger pull.

Binary stars, pairs of stars that orbit each other, are very common, and many Sun-like stars have a companion. These pairs are the main way astronomers measure the masses of stars directly. Newton’s version of Kepler’s third law turns the size of the orbit and the time for one orbit into the pair’s total mass.

To split that total between the two stars, astronomers find each star’s distance from their shared balance point, the centre of mass. It works like a see-saw, where a heavier child sits nearer the pivot. The same logic gives the Sun’s mass from Earth’s orbit, and Jupiter’s mass from its moons.

Whirling a ball on a string is a standard physics demonstration in American high schools. Every American student has also seen videos from NASA, the American space agency, of astronauts floating inside their ship.

Picture a rock being blasted off Mars. Roughly 17 million years ago, an asteroid struck Mars and threw the rock into space. It drifted through space for a long time and finally fell on Antarctica.

Its name is a code. ALlan Hills is the place in Antarctica where it was found, 84 stands for 1984, and 001 is the specimen number. Its chemistry matches a family of meteorites known to come from Mars. Some of them hold trapped gas identical to the Martian atmosphere measured by NASA’s Viking landers in 1976.

Why are so many meteorites found in Antarctica? Dark rocks stand out on white ice, and the cold preserves them. Moving ice also gathers them in certain spots, like a very slow conveyor belt.

In chemistry, “organic” means carbon-based. PAHs, short for polycyclic aromatic hydrocarbons, are molecules built from several linked rings of carbon atoms.

In 1996 McKay’s team offered several lines of evidence. Besides the PAHs, there were carbonate globules, tiny magnetite crystals and worm-like microscopic shapes. “Today, rock 84001 speaks to us across all those billions of years and millions of miles,” President Clinton said on TV.

The announcement was huge news in America, and it boosted NASA funding for astrobiology, the search for life beyond Earth. Americans often quote Carl Sagan’s maxim “extraordinary claims require extraordinary evidence” about it. Since then, NASA rovers have kept searching. Perseverance, which landed in 2021, has found rocks with possible, but unconfirmed, signs of past microbial life, and it is collecting samples for future return to Earth.

Picture Milutin Milanković, a Serbian engineer and mathematician whose name is also spelled Milankovitch. For decades he calculated by hand how changes in Earth’s orbit alter the summer sunlight reaching the far north. Earth’s orbit and axis change in three slow cycles. The first is eccentricity, how stretched the orbit is, on a cycle of about 100,000 years.

The second is obliquity, the tilt of the axis, which moves between about 22 and 24.5 degrees on a cycle of about 41,000 years. The third is precession, the wobble of the axis, like a spinning top, on a cycle of about 23,000 years. The key idea is simple. If northern summers are too cool to melt the winter snow, ice sheets grow year after year.

The record of past ice comes from isotopes, forms of the same element with different weights. Water containing light O-16 evaporates more easily, so the snow that builds ice sheets is rich in O-16. During ice ages, the oceans are left relatively richer in O-18. Tiny shelled plankton called foraminifera record the ocean’s ratio in their shells, which pile up on the seafloor layer by layer like the pages of a diary.

In 1976 a landmark paper by Hays, Imbrie & Shackleton, “Variations in the Earth’s Orbit: Pacemaker of the Ice Ages”, found the predicted cycles in deep-sea cores. The last ice age peaked about 20,000 years ago. Ice covered Canada and the northern US, sea level was about 120 m lower, and a land bridge called Beringia joined Siberia to Alaska.

Big volcanic eruptions throw sunlight-blocking particulates, or fine particles, high into the atmosphere. Tambora in Indonesia erupted in 1815 and caused 1816’s “Year Without a Summer”. Pinatubo in the Philippines erupted in 1991 and cooled the globe by about 0.5 °C for a year or so.

Orbital cycles act over tens of thousands of years. So they can’t explain the rapid warming since 1900, which is driven by greenhouse gases. In America, climate change is a politically polarised subject, and “it’s just natural cycles” is a common sceptic argument. That is why many Americans have heard of orbital cycles in that debate.

In 1929 Edwin Hubble, building on theory by Georges Lemaître, showed that farther galaxies are moving away faster. The universe is expanding, and this is the basis of the Big Bang theory. Think of raisin bread rising in the oven. As the dough swells, every raisin moves away from every other, and the farthest ones move apart fastest.

Before 1998, astronomers pictured three classic fates for the universe, like a ball thrown upward that may fall back or escape. In a closed universe, the density is above critical, so gravity halts the expansion and reverses it into a “Big Crunch”. In an open universe, the density is below critical, and the universe expands forever. In a flat universe, the density is exactly critical, so the expansion slows forever but never quite stops.

How can astronomers weigh things they cannot touch? By Newton’s laws, how fast something orbits depends on how much mass lies inside its orbit. In other words, speed reveals mass. That is why astronomers can “weigh” matter they cannot see, by measuring the speeds of matter they can see.

The idea of unseen dark matter goes back to Fritz Zwicky in 1933. In the 1970s Vera Rubin and Kent Ford made galaxy-rotation measurements of this kind. Rubin never won a Nobel, an omission that is often cited. The Vera C. Rubin Observatory in Chile is named after her.

Then came the 1998 twist. The expansion turned out to be accelerating, because of something called “dark energy”. Overall, the universe is very close to critical density, but mostly in the form of dark energy rather than matter.

In America, Rubin is a celebrated woman scientist, often cited in debates about women in science (see Topic 1). In 2019 Congress, the American parliament, named the observatory after her. It was the first US national observatory named for a woman.

Comets are icy bodies from the outer solar system. In 1950 Fred Whipple called them “dirty snowballs”. Near the Sun, their ice turns to gas and frees dust, which forms the comet’s tails and, over many orbits, a stream of dust. Halley’s Comet, which comes back about every 76 years and is next due in 2061, is the most famous.

A meteor shower happens when Earth crosses such a stream, on the same dates each year. The meteors seem to fly out from one spot in the sky, like spokes from the hub of a wheel. Each shower is named after the constellation at that spot. The Perseids come in August, the Leonids in November and the Geminids in mid-December, one of the year’s richest showers.

The Geminids’ parent, identified in 1983, is 3200 Phaethon. It is an unusual rocky body that behaves like a burnt-out comet. Small gravitational tugs, mostly from Jupiter, slowly alter orbits. This is called perturbation.

Earth moves at about 30 km per second, or roughly 1.6 million miles a day. Americans use miles, and a mile is about 1.6 km.

To study such slow changes, astronomers run a simulation. A computer applies the laws of gravity to thousands of test particles over a long span of time.

In America, the news and NASA publicise each year’s showers. Watching the August Perseids is a summer camping tradition, so “meteor shower” is an everyday American phrase.

From most of India, you can see Omega Centauri with the naked eye, low in the southern sky. It is the Milky Way’s biggest globular cluster: a dense, ancient ball of stars orbiting in the galaxy’s halo, the roughly round region around its disc. Such clusters are among the oldest objects in the galaxy. Open clusters, such as the Pleiades, are the opposite: young, loose and lying in the disc.

How can anyone tell a cluster’s age? All its stars were born together, but heavy stars burn out faster. So the heaviest stars that are still burning hydrogen act as a clock. The older the cluster, the lighter its heaviest survivors.

On how the galaxy formed, there are two schools. The top-down school says it formed in a rapid collapse, like a ball of dough flattening into a roti in one go. Eggen, Lynden-Bell and Sandage set out this view in 1962.

The bottom-up school says it was assembled from smaller pieces. Larson argued for this, and so did Searle and Zinn in 1978.

The name Palomar 12 comes from California’s Palomar Observatory. Its 200-inch telescope was the world’s largest from 1948 to the mid-1970s and became an icon of American astronomy.

Spread the same butter over a bigger slice of toast, and the layer gets thinner. Surface brightness, or brightness per patch of sky, works the same way. Spread the same stars over a bigger area, and each patch looks fainter. Many LSB galaxies are fainter than the natural glow of the night sky itself.

Sky surveys have a weakness: they find what is easiest to see. It is like the old joke about the drunk man who looks for his lost keys under a streetlight, because that is where the light is. This is called selection bias.

For a long time, galaxy catalogues favoured bright galaxies. The classic LSB example, Malin 1, was found in 1986. It is a spiral several times wider than the Milky Way.

Now a word that sounds harder than it is. Baryons are ordinary matter: the protons and neutrons inside atoms. Electrons are too light to matter here. “Non-baryonic” dark matter, made of unknown particles, is a separate issue.

Helium can act as a baryon counter. In the first minutes after the Big Bang, roughly a quarter of ordinary matter fused into helium. Traces of deuterium and lithium were made too. How much of each was made depends on the density of baryons, so measuring these amounts gives a count that does not rely on starlight.

About 66 million years ago, an asteroid roughly 10 km across ended the age of the dinosaurs. Asteroids are rocky leftovers from the time the planets formed. Most of them lie in the belt between Mars and Jupiter. They range in size from boulders up to Ceres, about 940 km across, which is now classed as a dwarf planet.

What is an asteroid like inside? A monolith is held together by the strength of solid rock. A rubble pile is a heap of boulders, gravel and dust, held together only by its own weak gravity. Spin a rubble pile too fast, and it flies apart.

A common pattern in data is the bell-shaped, or normal, distribution, in which values bunch around the average, with fewer and fewer towards the extremes. Think of the heights of adults in a big crowd. Most are close to the average, and very few are very tall or very short. Those thin ends of the curve are its “tails”.

Another key idea is escape velocity, the lowest speed needed to break free of a body’s gravity. For Earth it is 11.2 km per second. For an asteroid 1 km wide, it is well under 1 metre per second, slower than walking. Pieces moving slower than this cannot get away from each other.

Spacecraft have now visited some asteroids. Japan’s Hayabusa photographed Itokawa, a rubble pile, in 2005, and Hayabusa2 collected samples from Ryugu in 2018–19. NASA’s OSIRIS-REx found Bennu’s surface so loose that the craft’s sampling arm sank in, as if into a ball pit. It brought a sample back to Earth in 2023.

All this matters for planetary defence: in 2022 NASA’s DART spacecraft deliberately rammed a small asteroid, Dimorphos, and changed its orbit. Whether a threatening asteroid is solid or rubble changes how you would push it off course. Hollywood films made the threat of a strike from space familiar to Americans: Armageddon and Deep Impact in 1998, and Don’t Look Up in 2021. DART itself was widely covered news across the US.

In 1915 Einstein published general relativity, his theory of gravity, and it predicted black holes. In 1916 Karl Schwarzschild worked out the first black-hole solution to its equations. The name “black hole” came much later, when John Wheeler made it popular in 1967. Around every black hole lies its event horizon, the point of no return: once past it, nothing can pass back out, not even light.

Black holes come in two main kinds. Stellar black holes have a few to tens of times the Sun’s mass, and they are left behind when giant stars collapse. Supermassive black holes have millions to billions of times the Sun’s mass, and they sit at the centres of most large galaxies. Astronomers have a simple weighing trick (p.65): the speed and distance of gas in orbit give the mass inside the orbit. Divide that mass by the volume it takes up, and you get a density.

M87 is a giant elliptical galaxy about 55 million light-years away. In April 2019 the Event Horizon Telescope, a planet-wide network of radio dishes, released the first-ever image of a black hole. It showed M87’s black hole, about 6.5 billion times the Sun’s mass, as a dark shadow inside a glowing ring. In 2022 the same network imaged our own galaxy’s black hole, Sagittarius A*, at about 4 million Suns.

NGC 4258 is a spiral galaxy about 24 million light-years away. In 1995 radio astronomers tracked natural microwave “lasers”, called masers, in a thin disc orbiting its centre. They revealed tens of millions of Suns’ worth of mass packed within a fraction of a light-year. It became one of the strongest early cases for a supermassive black hole.

The odd names come from old catalogues. “M” numbers come from the list of Charles Messier, an 18th-century French comet-hunter. He listed fuzzy objects that people should not confuse with comets. “NGC” stands for the New General Catalogue of 1888.

The 2020 Nobel Prize in Physics went to Roger Penrose for black-hole theory. It also went to Reinhard Genzel and Andrea Ghez for the supermassive object at our galaxy’s centre. In the US, the 2019 image was front-page news. A photo of Katie Bouman, a young American computer scientist on the team, reacting to it went viral. And the film Interstellar, from 2014, had already made black holes part of pop culture.

About 4.5 billion years ago, the Moon probably formed from debris after a Mars-sized body hit the early Earth. Like the Earth, it is built in layers. It has a light crust, a denser mantle underneath and a small core.

The crust “floats” on the denser mantle, which flows very slowly, rather like ice floating on water. Take weight off the top, and the material below rises to make up for it. This balance is called isostasy. The same principle gives mountains deep “roots”.

Look at the full Moon and you will see dark patches called “seas”, or maria, though they hold no water. They are plains of lava that later flooded many of the Moon’s impact basins. Impact basins are the biggest craters, hundreds of kilometres across, and many are ringed by mountain chains, one circle inside another. That is why they are called “multi-ring” basins.

Gravity can be measured from orbit. Extra or missing mass below a spot slightly speeds up or slows down a spacecraft passing overhead, and tracking its radio signal reveals the change. In 1968 NASA’s Lunar Orbiter craft were unexpectedly tugged over certain basins. These spots were named mascons, short for “mass concentrations”, and they were a navigation headache for the Apollo landings.

Those Apollo landings, in 1969–72, are still a point of national pride in America. The next US Moon mission was Clementine, in 1994, a joint mission of NASA and the Pentagon, America’s defence headquarters. It mapped the Moon’s surface and gravity, and it found hints of ice in polar craters that are always in shadow.

Later, in 2011–12, NASA’s twin GRAIL probes made the most detailed gravity map of the Moon. Today NASA’s Artemis programme aims to send astronauts back to the Moon, partly for that polar ice.

In January 1610, Galileo turned one of the first telescopes on Jupiter and discovered these four moons. That is why they are called the Galilean moons. Moons circling something other than Earth supported Copernicus’s Sun-centred system, in which the Earth goes round the Sun. This was part of the clash behind Galileo’s trial in 1633 (see Topic 8.2).

Io is the most volcanically active body in the solar system, with about 400 active volcanoes. Voyager 1 first saw its eruptions in 1979. Its heat comes from tidal flexing: Jupiter’s gravity kneads Io, squeezing and stretching it. A rubber ball warms up in the same way when you squeeze it again and again. Regular tugs from Europa and Ganymede keep Io’s orbit slightly oval.

Europa has a cracked shell of ice over a global ocean of liquid water. That makes it one of the best places to look for life beyond Earth. NASA’s Europa Clipper launched in 2024 and is due to arrive in 2030.

Ganymede is the largest moon in the solar system, bigger even than the planet Mercury, and it has its own magnetic field. Europe’s space agency, ESA, launched its JUICE probe in 2023, and it will orbit Ganymede in the 2030s. Callisto has one of the most heavily cratered surfaces in the solar system.

Why are the Sun’s inner planets rocky? Near the young Sun it was too hot for ice to freeze, so only rock and metal condensed into solids. Beyond a boundary called the frost line, ice was plentiful.

Pictures from NASA missions fill American textbooks: Voyager in 1979, then the Galileo spacecraft from 1995 to 2003, then Juno from 2016. They show Io’s volcanoes and Europa’s ice.

Picture an eclipse of the Sun in 1919. An expedition led by Arthur Eddington measured starlight bending as it passed the Sun, and the result made Einstein world-famous. In Einstein’s general relativity, mass curves space, so light passing a massive object is bent, as if by a lens. This is gravitational lensing.

Huge lenses, such as clusters of galaxies, bend light into arcs and multiple images. A small lens, such as a MACHO, makes a star behind it brighten for a while. A MACHO could be a brown dwarf, a “failed star” too small to fuse hydrogen. It could also be a faint dwarf star, a neutron star or a black hole.

Colours matter here. A glass prism splits white light into a rainbow, because it bends each colour by a different amount. Gravity, by contrast, is achromatic: it bends every colour by the same amount. A pulsating variable star is different: it changes temperature as it brightens, and hotter means bluer, so its colours change unequally.

Stars that change in brightness on their own are called variable stars. In 1912 Henrietta Leavitt found that the pulse rate of one kind, the Cepheid variables, reveals their true brightness. She was one of Harvard Observatory’s women “computers”, people who did calculations by hand, so her story also links to Topic 1. Her discovery turned Cepheid variables into cosmic yardsticks, which Hubble later used.

The Large Magellanic Cloud is a small satellite galaxy, a companion of our own, about 160,000 light-years away. It is visible to the naked eye from the Southern Hemisphere and is named after Magellan’s voyage. Looking at it means looking through our galaxy’s halo at millions of stars in the background. In the 1990s several surveys went hunting for MACHOs: the US–Australian MACHO Project, France’s EROS and Poland’s OGLE.

The surveys found some events, but too few for MACHOs to make up most of the halo. Most dark matter is now thought to be exotic matter that is not made of atoms. Microlensing later became a way to discover planets. The name “MACHO” is a pun on American slang. The rival dark-matter candidates are called WIMPs, weakly interacting massive particles, so the debate is “macho”, the tough guy, against “wimp”, the weakling.

In 1905 Einstein set a speed limit in his theory of special relativity. No object, signal or piece of information can travel faster than light in a vacuum, about 300,000 km per second. If signals could, an effect could come before its cause. So physicists treat superluminal, or faster-than-light, claims with great caution.

In the 1920s physicists such as Heisenberg, Schrödinger and Bohr built quantum mechanics, the physics of the very small. At the scale of atoms, particles behave like waves of probability. When such a wave hits a barrier, it does not stop dead but fades inside it. If the barrier is thin enough, a little of the wave leaks out the other side, and that leak is the chance of tunnelling.

That chance “declines exponentially” as the barrier gets thicker: each extra slice of barrier multiplies it by the same small fraction. Picture a row of gates, each letting only one person in ten through. After three gates, only one person in a thousand has got through. In the same way, a slightly thicker barrier makes tunnelling vastly rarer, and that is why balls never pass through walls.

Tunnelling is real and everyday: in 1928 George Gamow showed that it explains a kind of radioactivity called alpha decay. It also lets protons in the Sun fuse even though they repel each other, and it makes flash memory in USB drives and SSDs work. The scanning tunnelling microscope, whose invention won a Nobel Prize in 1986, depends on it too. In the 1980s John Clarke, Michel Devoret and John Martinis showed that a whole electric circuit, big enough to hold in your hand, can tunnel. This large-scale, or “macroscopic”, quantum tunnelling won them the 2025 Nobel Prize in Physics and is groundwork for today’s quantum computers.

How do physicists test a faster-than-light claim? They time particles, often photons (particles of light), as they cross a barrier, and compare that with the same trip without the barrier. Reading these timings is notoriously tricky, so treat any “faster than light” result as a claim, not a settled fact. Remember the school formula, “speed equals distance divided by time”, and keep track of which quantity is growing and which is fixed.

Americans have an everyday phrase for faster-than-light travel: “warp speed”, from Star Trek. The US government even named its 2020 COVID-vaccine drive “Operation Warp Speed”.

Picture southern Germany in 1861, just two years after Darwin’s Origin. In the fine Solnhofen limestone of Bavaria, a fossil turns up. It is Archaeopteryx, “ancient wing”, about 150 million years old. It comes from the Late Jurassic, a time deep in the age of dinosaurs, and it lived in a hot, dry region of lagoons with scrubby plants.

Archaeopteryx is a mosaic, a mix of parts: bird-like feathers and wings, but dinosaur-like teeth, clawed fingers and a long bony tail. That made it the textbook “transitional fossil”. Its closest dinosaur cousins are the maniraptorans, or “hand-snatchers”. They belong to the theropods, the mostly meat-eating dinosaurs, and include the “raptors” Velociraptor and Deinonychus.

The two classic answers to how flight began take their names from Latin. Arboreal comes from arbor, “tree”, and cursorial from cursor, “runner”. In the ground-up idea, small running, leaping dinosaurs used their feathered arms for lift, balance or speed, while chasing prey or escaping. In time, they became airborne.

Feathers came before flight. Many feathered dinosaurs could not fly. So feathers probably served first for warmth, for showing off, or for covering eggs in the nest, and were borrowed for flight only later. Biologists call a re-used trait like this an exaptation, rather like an old sari that ends up as a curtain.

Gliding and flapping flight work in different ways. A glider, such as a flying squirrel or India’s own Draco “flying lizard”, trades height for distance. Powered flight needs a flight stroke, the flapping beat of the wings.

Americans grew up with the 1993 film Jurassic Park, whose “Velociraptors” were as big as a man and covered in scales. The real Velociraptor was about the size of a turkey and had feathers. Its arm bone even shows quill knobs, the bumps where feathers were anchored. Many US news stories about new feathered dinosaurs open with a nod to Jurassic Park.

The idea that birds are related to dinosaurs is older than you might think. In the 1860s T. H. Huxley, known as “Darwin’s bulldog”, pointed out similarities between birds and dinosaurs. Then in 1926 Gerhard Heilmann wrote an influential book that rejected the link, partly because theropods seemed to lack clavicles, or collarbones. In 1969 John Ostrom described Deinonychus, an agile, bird-like dinosaur, and revived the idea. Since 1996, dozens of feathered dinosaurs from China have persuaded most palaeontologists.

Birds and theropods share many features: hollow, air-filled bones, three main toes pointing forward, wishbones and a swivelling wrist. They also share a habit, nesting and brooding, which means sitting on eggs to keep them warm. In Mongolia in the 1990s, fossils of oviraptorids were found sitting on their nests in a brooding posture. The name holds an irony. Oviraptor means “egg thief”, because the first one, found in 1924, was wrongly thought to be stealing eggs.

The furcula, or wishbone, is two collarbones fused into a “V”. In flying birds it flexes like a spring during each wingbeat. Wishbones are now known in many theropods, including Tyrannosaurus and Velociraptor.

Fossils are rare. Most animals rot or are eaten by scavengers before they can be buried in sediment and mineralised, or turned to stone. So the fossil record is patchy. Archaeopteryx itself is known from only about a dozen specimens, all from Solnhofen in Bavaria, Germany.

Bird lungs work differently from ours. Our lungs fill and empty like a balloon, with air going in and out the same way. In birds, air sacs pump air one way through rigid lungs. This efficiency lets bar-headed geese fly over the Himalayas.

Falsifiability is an idea from the philosopher Karl Popper. A scientific claim must, in principle, be open to being shown false by evidence. For example, “this coin always lands heads” is falsifiable, because a single tails would show it false.

At Thanksgiving, American families dry the turkey’s wishbone, and two people pull it apart. Whoever gets the bigger piece “gets a wish”. American children see dinosaurs in museums such as the Smithsonian in Washington and Chicago’s Field Museum, home of “Sue”, a famous T. rex. Many US textbooks and museums now present birds as living dinosaurs.

In 1842 the scientist Richard Owen coined the word “dinosaur”, which means “terrible lizard”. For the next century, people pictured dinosaurs as slow, sluggish giant lizards that dragged their tails along the ground.

From the late 1960s, that picture changed. In the Dinosaur Renaissance, Ostrom (see p.80) and his student Robert Bakker recast dinosaurs as active, bird-like animals. Bakker is an American palaeontologist, or fossil scientist. He is famously colourful and a champion of “hot-blooded” dinosaurs. His popular 1986 book, The Dinosaur Heresies, took the warm-blooded case to the public.

Warm or cold blood is a question of physiology, or how an animal’s body works. Birds and mammals are endotherms. They make their own body heat, keep a steady temperature, eat a lot and can grow fast. Most reptiles, amphibians and fish are ectotherms, which rely on outside heat, like a lizard basking in the sun. They need far less food and usually grow more slowly.

Think of an endotherm as a house with its own heater: always warm, but with a big fuel bill. An ectotherm is a house with no heater, warm only when the sun shines in. In fact, a “cold-blooded” lizard in the sun can be quite warm, so scientists prefer the words endotherm and ectotherm.

Palaeontologists study long-dead animals by comparing them with living ones. One tool is bone histology, the study of bone tissue under a microscope. Researchers cut paper-thin slices of fossil bone and examine them. The way the fibres are arranged, and how thickly the bone is packed with blood-vessel channels, show how fast it was laid down. Armand de Ricqlès is a French specialist in bone tissue.

Ordinary Americans watched the dinosaur image flip within one generation. Old films showed slow swamp monsters. Then came the fast, clever animals of Jurassic Park in 1993. The film’s scientific adviser was the Montana palaeontologist Jack Horner, and its hero, Dr Alan Grant, was partly modelled on him.

Picture the middle of Los Angeles, a big city in California. Here, natural asphalt seeps up from oil deposits underground. It is the same kind of sticky black stuff that Indians call tar on their roads. In Spanish, brea means “tar” and la means “the”, so “the La Brea Tar Pits” literally means “the the tar tar pits”.

Animals got stuck in the sticky asphalt, which was often hidden under water or leaves. Their struggles drew predators and scavengers, and those got stuck too. So La Brea became a predator trap. Among its millions of fossils, meat-eaters, or carnivores, vastly outnumber plant-eaters.

The most common large mammal there is the dire wolf, with thousands of individuals. Next comes the sabre-toothed cat Smilodon, California’s state fossil. Diggers have also found American lions, short-faced bears, coyotes, Columbian mammoths and giant ground sloths.

The Pleistocene lasted from about 2.6 million to 11,700 years ago. It was the “Ice Age” epoch, a long era when ice sheets spread again and again and giant mammals, called megafauna, roamed. Most of North America’s megafauna disappeared around 13,000–10,000 years ago. Climate change and hunting by newly arrived humans are the leading suspects.

But a fossil sample is not a random sample of a living population. It can be skewed by the ages of the animals that died, a demographic bias. It can be skewed by what happened to the bones after death, a preservational bias studied in taphonomy. Or one unusual site can skew it, a local bias. A careful study rules these out before trusting a biological explanation.

Today the tar pits sit on Wilshire Boulevard’s “Museum Row”, next to the Los Angeles County Museum of Art. Life-size mammoth statues stand in the lake pit. Generations of Southern California schoolchildren have visited on field trips, and the digging is still going on.

Picture Africa roughly 4 to 2 million years ago. Upright-walking human relatives called australopithecines, or “southern apes”, lived there. They had chimp-sized brains and ape-like faces. Their big molars, or back teeth, had thick enamel, the hard outer coat of a tooth. Strictly speaking, they were a group of species, not one species.

Think of evolution as a family tree. About 6–7 million years ago, one branch forked: one side led to chimpanzees, the other to us. Hominins are humans and all the extinct relatives on our side of the fork, including the australopithecines. Our own group of closely related species, the genus Homo, appears roughly 2.8–2.3 million years ago.

In 1924 Raymond Dart recognised the first australopithecine, the Taung Child, in South Africa. “Lucy”, found in Ethiopia by Donald Johanson in 1974, is an A. afarensis about 3.2 million years old, named after a Beatles song. The Laetoli footprints in Tanzania, about 3.6 million years old, prove upright walking. In 1959 Mary Leakey found “Nutcracker Man”, a huge-jawed relative. Later chemical studies suggested it ate mostly grasses and grass-like sedges rather than nuts.

Under a microscope, chewing leaves scratches and pits on the enamel. Hard, brittle foods such as seeds, nuts and bone tend to leave pits. Tough foods such as leaves and grass stems leave long scratches. Researchers match the patterns on fossil teeth against living animals whose diet is known.

Three scholars are worth knowing. In 1970 Clifford Jolly put forward a “seed-eater” model, comparing early hominins to gelada baboons, which eat grass seeds in the Ethiopian highlands. Around 1980 Alan Walker pioneered micro-wear studies of hominin teeth. Frederick Szalay proposed a hunting-and-scavenging model of how hominins began.

In the US, “Lucy” is a household name, and her fossil toured American museums from 2007 to 2013. Yet teaching human evolution remains politically sensitive in some states. In 2005 a federal court case, Kitzmiller v. Dover, barred “intelligent design” from science classes in public schools, which in America are government-run schools. See Topic 8.2 for more on challenges to religion.

Run a finger down your back and you can feel the bumps of your backbone. Animals with a backbone are called vertebrates: fish, amphibians, reptiles, birds and mammals. They belong to a wider group, the chordates, which all have a notochord at some stage of life. It is a stiff but bendy rod along the back, like a thin bamboo cane. Human embryos have one too, and remnants of it survive in the cores of our spinal discs.

Between about 540 and 520 million years ago, most animal groups first appear in the fossil record. This burst is called the Cambrian explosion, and its famous fossil sites include the Burgess Shale in Canada and Chengjiang in China. Arms races between predators, the hunters, and their prey are a major theme of this period. In an arms race, each side keeps answering the other: better weapons on one side, better armour on the other.

The first vertebrates had no jaws, and lampreys and hagfish are their living jawless descendants. The ostracoderms, or “shell-skins”, were extinct jawless fish covered in bony armour plates. They lived about 480–360 million years ago. Jaws evolved later still. In biology, “primitive” means close to the ancestral form, or branching off early on the family tree. It does not mean crude or inferior.

In 1856, scientists first described tiny, tooth-like fossils called conodont elements, most of them under a millimetre long. They are common and changed quickly over time, so geologists use them to date rock layers. It is like dating an old family photo by the mobile phone in someone’s hand. Their colour also changes with heat, which helps oil explorers judge how “cooked” a rock has been.

The animals themselves were eel-shaped, mostly a few centimetres long, with large eyes. The first whole-body fossils came from near Edinburgh, in Scotland.

Many educated Americans know the Cambrian story from Stephen Jay Gould’s 1989 bestseller Wonderful Life, about the strange early animals of the Burgess Shale.

Picture an old stone arch over a gateway. The single wedge-shaped stone at the very top is the keystone. Pull it out and the whole arch collapses.

In 1963, the ecologist Robert Paine of the University of Washington began one of ecology’s most famous experiments. His site was a stretch of rocky shore on the coast of Washington State, in the US north-west. There he kept removing Pisaster sea stars, a kind of starfish. Mussels took over the space, and the number of species in the plot dropped sharply. In 1969, Paine coined the term keystone species.

A keystone is not the same as a dominant species. A dominant species matters because there is so much of it, like the main tree species of a forest. A keystone matters far more than its numbers suggest. Ecology’s standard test is the removal experiment: take a species away and watch what changes. But the results can be indirect, slow to show and tied to one particular site.

Textbooks name other keystones too. Sea otters eat sea urchins, which would otherwise devour kelp forests, the underwater forests of giant seaweed. Beavers are “ecosystem engineers”, whose dams create wetlands. Fig trees feed tropical animals when little else is fruiting.

Wolves are another textbook case. In 1995, they were brought back to Yellowstone. They changed how elk behaved and how many elk there were, with knock-on effects on plants along the streams. Such a chain of effects down the food chain is called a trophic cascade, though how strong this one is remains debated.

Yellowstone, set up in 1872, was America’s first national park. The wolves’ return there is the country’s best-known ecology story, retold in a viral 2014 video, “How Wolves Change Rivers”. Sea otters, for their part, are beloved mascots of the California coast, for example at Monterey Bay Aquarium.

In 1942, the German-American biologist Ernst Mayr formalised the biological species concept, the definition most school textbooks teach. One word in it matters a lot: fertile, meaning able to have young. A horse and a donkey can mate and produce a mule, a hybrid, or cross, of the two. But a mule is almost always sterile, so horses and donkeys remain separate species. Lion–tiger crosses, called “ligers”, exist only in captivity.

Real hybrids give biologists headaches. Wolves, coyotes, dogs and jackals can all produce fertile hybrids. In eastern North America, “coywolves” carry wolf, coyote and dog DNA, and whether the endangered red wolf is a separate species is disputed. In the Canadian Arctic, wild hybrids of polar bears and grizzly bears, nicknamed “pizzly” bears, have turned up.

Even humans and Neanderthals, our extinct cousins, interbred. Most people of non-African descent carry about 1–2% Neanderthal DNA. Svante Pääbo won the 2022 Nobel Prize for this genetic work.

Over the years, biologists have proposed more than 20 species concepts. It is a bit like defining “middle class” in India: everyone uses the term, but people draw the line in different ways. The morphological concept is based on body form, and it is the only option for fossils. The phylogenetic concept takes the smallest group with a shared ancestry, often judged by DNA. The ecological concept is based on a distinct way of life.

The lines matter in law too. The US Endangered Species Act of 1973 protects species, subspecies and “distinct population segments”. So where biologists draw the lines decides what the law protects. India has its own example. The Asiatic lions of Gir were long treated as a separate subspecies, but a 2017 revision grouped them with West and Central African lions.

In America, fights over the Endangered Species Act make national news. In 1978, in the Supreme Court case TVA v. Hill, a small fish called the snail darter halted a dam. In the 1990s, the northern spotted owl was pitted against logging. Today, coyotes live in almost every US city, including New York and Chicago.

Picture Thomas Hunt Morgan’s “fly room” at Columbia University in the 1910s. Ever since, the fruit fly, Drosophila melanogaster, has been the workhorse of genetics. It is cheap to keep, and it breeds in about ten days. Roughly three-quarters of known human disease genes have a matching gene in the fly.

A mutation is a change in a gene’s DNA. Fly genes are named after what goes wrong when they mutate, and the names are written in italics. A fly with a faulty dunce gene learns poorly, and a faulty fruitless gene leads to abnormal courtship. It is like naming a car part after the rattle the car makes when that part breaks.

Shaker was found in the late 1960s. In 1987 it turned out to carry the recipe for a potassium channel, a tiny pore that helps a nerve cell reset after it fires. It was the first such gene ever isolated. It opened up the study of channel defects behind some epilepsies and heart-rhythm disorders.

The gene period, or per, was first described in 1971 by Ronald Konopka and Seymour Benzer at Caltech. Benzer was the pioneer of fly behaviour genetics. The excerpt breaks off just as it reaches what per controls, so this guide does not fill in that gap.

Height is shaped by many genes of small effect, plus the environment. Most behaviours are shaped the same way, and such traits are called polygenic. Think of a cricket team’s total: many batters each add a few runs, and the pitch matters too. Modern genome-wide scans, which search all of an animal’s DNA, can now hunt for these many genes together.

Americans often see headlines announcing “the gene for” some behaviour, such as risk-taking or novelty-seeking. Scientists usually reply that genes shift the odds rather than dictate behaviour. The argument over what counts as a “behavioural gene” is part of that conversation.

Imagine an animal facing a strange new food. Finding out by trial and error can be fatal, so watching others is a cheap shortcut. This is social learning, and it ranges from true imitation to simply being drawn to the places where others are feeding. Think of a new student in a college canteen who watches what the seniors order before choosing.

Some cases are famous. In 1920s Britain, blue tits learned to peck open the foil caps of milk bottles left on doorsteps, and the habit spread across the country. In 1953, on Koshima island in Japan, a young macaque started washing sweet potatoes in water, and her troop picked it up. Chimpanzee groups have their own tool “traditions”.

Food choice has a classic study of its own. In the 1980s, Bennett Galef showed that rats learn which foods are safe by smelling food on the breath of other rats.

Another key idea is taste aversion, the “Garcia effect”, studied in the 1950s–60s. One bad meal is enough: an animal that falls ill after eating a food avoids it from then on, even if the illness came hours later. Many people know this: after one bad night following a plate of prawns, they avoid prawns for a long time. That raises a question: can an animal learn such a dislike just by watching others, without getting sick itself?

Colour can carry a warning too. Many toxic animals are brightly coloured, and birds learn to avoid them. In the 1960s, Lincoln Brower showed that blue jays vomit after eating monarch butterflies, which carry poisons from the milkweed plant, and afterwards avoid them.

The red-winged blackbird is one of North America’s most common birds. The house sparrow was brought to New York from Europe in the early 1850s. It is the same gauraiya you see in Indian towns. An Indian conservation group started World Sparrow Day, 20 March, in 2010.

Picture two cells side by side under a microscope. The first is a prokaryote, Greek for “before the kernel”. It is tiny, and its DNA floats loose inside it, usually as a single loop. It has no nucleus and no membrane-wrapped organelles, which are small, specialised structures inside a cell.

The second cell is a eukaryote, or “true kernel”. It is much larger, and its DNA is enclosed in a nucleus. Inside are organelles such as mitochondria, which supply energy, and, in plants, chloroplasts, which make food from sunlight by photosynthesis. Animals, plants, fungi such as yeast, and protists such as amoebas are all eukaryotes.

Mitochondria and chloroplasts have a surprising past. They were once free-living bacteria that an ancestral cell swallowed. This idea, endosymbiosis, was championed by Lynn Margulis from 1967, and it is now accepted.

Inside a cell, DNA is copied into RNA, and the RNA is “translated” into proteins. Proteins are chains built from 20 kinds of amino acids. The genetic code used for this translation is almost the same across all life, which is strong evidence of a common ancestor. Enzymes are proteins that speed up chemical reactions, and comparing their sequences across living things reveals how closely those living things are related.

From the 1960s on, biologists compared molecules more and more, not just structures seen under a microscope. Proteins, RNA and DNA helped them work out how living things are related. Indian school biology, in the NCERT books, is built around Whittaker’s five kingdoms from 1969. They are Monera, which are the prokaryotes, then Protista, Fungi, Plantae and Animalia.

In America, Yellowstone’s hot springs gave science Thermus aquaticus, a heat-loving bacterium found in the 1960s. Its heat-proof enzyme, “Taq”, powers PCR, the DNA-copying method behind COVID-19 tests. PCR was honoured with a Nobel in 1993.

Picture a polio patient lying inside an “iron lung”, a tank-like machine that kept patients alive when their breathing muscles failed. Polio is caused by a virus that spreads mainly through dirty water, food and hands. Most infections cause mild symptoms or none at all. But in about 1 in 200, the virus destroys nerve cells in the spinal cord, causing paralysis.

Age mattered because babies carry protective antibodies, germ-fighting molecules, from their mothers. So infections in infancy were usually mild and left lasting immunity, or protection. The mother’s antibodies are like a borrowed umbrella that is soon handed back. Cleaner cities delayed the first infection until that umbrella was gone.

Typhoid is a different disease, caused by bacteria and spread through water and food dirtied by sewage. In the early 1900s, filtered, chlorinated water and sewer systems cut it sharply in US cities. A New York cook named Mary Mallon had no symptoms but infected dozens of people. Nicknamed “Typhoid Mary”, she was forcibly isolated for decades.

Scientists who study disease ecology see epidemics as the product of three things together: the microbe, the host it infects and the environment. The picture also includes any carriers, called “vectors”, and the way people live and use land.

In the United States, a major polio epidemic centred on New York in 1916, and cases peaked in 1952 at about 58,000. In 1955, Jonas Salk’s injected vaccine was declared safe and effective after a trial in about 1.8 million children. Albert Sabin’s oral drops followed in the early 1960s, and India’s Pulse Polio campaign used the same kind of drops from 1995. India’s last wild polio case came in January 2011, and the WHO certified the country polio-free in 2014.

President Franklin D. Roosevelt, himself paralysed at 39 in 1921, founded the charity that became the March of Dimes in 1938. Since 1946, his face has been on the dime, the ten-cent coin, in honour of the March of Dimes. In the 1950s, polio was America’s great fear, and pools and summer camps closed in “polio season”. Salk became a national hero, and when asked who owned the patent on his vaccine, he replied, “Could you patent the sun?”

Picture a pond full of tadpoles that will one day hop about on land as frogs. Many amphibians live this kind of “double life”, and that is what their name means. The group includes frogs, toads, salamanders, newts and limbless caecilians. Their thin, permeable skin lets water and oxygen pass through, and pollutants too.

Because of that skin and double life, amphibians are often called early-warning signals for the environment, or indicator species. People call them the “canary in the coal mine”. Miners once carried canaries, which collapse from toxic gas before humans do.

The alarm spread among scientists around 1989–90. Researchers comparing notes found frog declines on several continents. Costa Rica’s brilliant orange golden toad, last seen in 1989, became the symbol of that alarm.

Ecologists separate steady trends, such as habitat loss and pollution, from random, or stochastic, shocks. A shock might be a drought, a disease outbreak or a run of bad breeding years. A large population absorbs such shocks, but a tiny one can be wiped out by them.

The Red List is kept by the IUCN, the global conservation authority. It sorts species into steps, from safest to worst: Least Concern, Near Threatened, Vulnerable, Endangered, Critically Endangered, Extinct in the Wild and Extinct.

Mark Twain’s famous story “The Celebrated Jumping Frog of Calaveras County”, from 1865, is taught in American schools. The California red-legged frog is thought to be Twain’s frog. The US government has listed it as threatened since 1996.

Picture a male lizard on a tree trunk, flashing a colourful throat fan called a dewlap as a signal. This is an anole. Anoles are small lizards, with hundreds of species across the Caribbean and the Americas. The green anole of the southeastern US is often sold as an “American chameleon”, because it turns from green to brown.

The Caribbean’s four big islands are called the Greater Antilles: Cuba, Hispaniola, Jamaica and Puerto Rico. Hispaniola is shared by two countries, Haiti and the Dominican Republic. Puerto Rico has been a US territory since 1898, and its people have been US citizens since 1917.

Biologists call anoles that specialise in one habitat ecomorphs, a term coined in 1972. They recognise six anole types, and the grass, trunk and twig types are three of them.

Each body fits its job. Long legs give speed on broad trunks. Short legs give careful footing on narrow twigs, just as people take small, careful steps along a narrow ledge. Long tails help with balance in grass.

Green anoles are everyday garden lizards in Florida and Georgia. In Florida, brown anoles from Cuba arrived as invaders and pushed the native green anoles higher into the trees. Within about 15 years, the green anoles evolved larger, stickier toe pads. This is a much-reported case of evolution happening in real time.

Picture a shaggy, black-coated bear ripping open a termite mound with its long, curved claws. It has a cream “V” on its chest. It can close its nostrils, and a gap in its front teeth plus mobile lips let it suck up termites like a vacuum cleaner, loudly. This is the sloth bear, named because early European naturalists thought it was related to the tree sloth.

The sloth bear lives mainly in India, with smaller populations in Sri Lanka and Nepal. Baloo in Kipling’s The Jungle Book, set in the Seoni forests, is usually identified as a sloth bear. For centuries, sloth bear cubs were captured to become street “dancing bears”. The practice ended in India in 2009, when the last ones were rescued.

There are eight bear species in the world: American black, brown, polar, Asiatic black, sun, sloth, spectacled and the giant panda. Brown bears include the grizzly. India hosts four of the eight: the sloth, Asiatic black, Himalayan brown and sun bears.

Eating ants and termites is called myrmecophagy, and these insects are tiny, low-energy food. So specialists such as anteaters and pangolins tend to have a low metabolic rate, burning energy slowly, like a small engine that sips fuel. Giant anteater pups ride on their mother’s back, and pangolin babies cling to their mother’s tail.

Biologists often test an explanation with the comparative method: they check other species. If the explanation is right, animals living under the same conditions should show the same behaviour. A species that has the condition but lacks the behaviour counts against the explanation.

America’s most familiar bear is the American black bear. Smokey Bear, the Forest Service’s fire-prevention mascot since 1944, is a black bear. The teddy bear is named after President Theodore Roosevelt. On a 1902 hunting trip, he refused to shoot a black bear that had been tied up.

Picture the ball-balancing “seal” at a circus. It is usually a California sea lion. Seals, sea lions and walruses are pinnipeds, which means “fin-footed”. They are sea mammals that give birth on land or ice.

Pinnipeds fall into three families. Phocids, the “true” or earless seals, have no ear flaps. On land they wriggle on their bellies, and in water they swim with their hind flippers. Elephant seals and hooded seals are phocids.

Otariids, the eared seals, include sea lions and fur seals, so the circus sea lion is one of them. They have small ear flaps and can turn their hind flippers forward to “walk” on land. Walruses form a family of their own.

Biologists have names for two ways of paying for motherhood. Mothers who pay from stored reserves are capital breeders, like people living off their savings. Mothers who feed as they go are income breeders, like people living on a salary. A mother who fasts while nursing is a capital breeder, and one who forages is an income breeder.

Blubber is a thick layer of fat under the skin. It keeps the animal warm in cold water and also stores energy, like a warm blanket and a packed lunch in one.

Since 1990, hundreds of California sea lions have hauled themselves out onto the docks of San Francisco’s Pier 39. The pier is now a top tourist sight. All US marine mammals have been protected since the Marine Mammal Protection Act of 1972.

Picture a single-celled alga living inside an intricate, glass-like shell of silica. This is a diatom, and diatoms live in oceans, lakes and wet sand. Like plants, they photosynthesise, making food from sunlight, so they need light. They are estimated to produce about a fifth of the oxygen on Earth.

Deposits of fossil diatoms, called diatomaceous earth, are used in filters and toothpaste. In 1867, Alfred Nobel used them to keep the nitroglycerine in his dynamite stable.

Tides are caused mainly by the Moon’s gravity. Most coasts get two high tides and two low tides a day. One tidal cycle averages about 12 hours 25 minutes. So each day’s low tide comes about 50 minutes later than the day before, like a train that runs a little later every day.

Circadian rhythms, from the Latin for “about a day”, run on about 24 hours. Sleep, hormones and jet lag all involve them (see p.62 and p.87). Circatidal rhythms run on about 12.4 hours. In the 1950s, fiddler crabs on US beaches were famously shown to keep their tidal activity rhythms even in lab tanks.

The classic test for an internal clock is to remove every outside cue, keeping light, temperature and pressure constant. If the rhythm keeps going, or “free-runs”, the timing must come from inside the living thing. Think of a person in a windowless room who still wakes at about the usual hour.

Picture a forest in summer with bare trees, as if winter had come early. Caterpillar outbreaks can do this to millions of hectares of forest. The caterpillars belong to the lepidoptera, a name that means “scale-wings”. They go through complete metamorphosis, a life in four stages: egg, caterpillar or larva (the eating stage), pupa in a cocoon or chrysalis, and winged adult.

One famous cycling species is the larch budmoth of the European Alps. Tree rings there show its outbreaks every 8–10 years for over a thousand years. Beyond insects, the textbook case is Canada’s lynx, a wild cat, and the snowshoe hare, which cycle about every ten years. The Hudson’s Bay Company recorded this cycle in its fur-trading records from the 1800s.

Lemmings, which are small rodents, cycle every 3–4 years. Their famous “mass suicide” is a myth, staged for a Disney documentary. Another key idea is density dependence. Some forces hit a population harder as it gets more crowded, such as food shortage or disease spreading between neighbours.

The nuclear polyhedrosis virus, or NPV, attacks caterpillars. Its particles are packed inside protein crystals called “polyhedra”, and these give the virus its name.

Another famous cycling species is the spongy moth, called the “gypsy moth” until scientists renamed it in 2022. In 1869 a French amateur naturalist, Trouvelot, was trying to breed silk moths near Boston when he accidentally let it escape. It has stripped the leaves of eastern US forests ever since. Today the US Forest Service uses an NPV spray called “Gypchek” against it, as a natural pesticide.

In outbreak years, spongy moth caterpillars strip whole hillsides in New England and the Midwest. In 1981 they stripped about 13 million acres. Americans there remember caterpillars “raining” from the trees and their droppings pattering down like rain.

Picture the citrus groves of California under attack from a pest called the cottony cushion scale insect. In 1888–89 an Australian ladybird, the vedalia beetle, was brought in, and it rescued the citrus industry. This was the founding success of biological control, which fights a pest with its natural enemies: predators, parasites or disease organisms. Classical biocontrol imports those enemies from the pest’s native range, the region it first came from.

India has tried this too. In 1983 it released a Mexican leaf beetle against Parthenium, an invasive weed known as “congress grass”. But some releases have famously backfired. In 1935 cane toads were released in Queensland, Australia, to eat sugar-cane beetles.

The toads ignored the beetles, spread across the continent and poisoned native predators. The small Indian mongoose was brought to Jamaica in 1872 and Hawaii in 1883 to kill rats in the cane fields. Instead, it devastated native birds and reptiles. It was like hiring a guard to catch burglars, only to see him rob the neighbours.

In England, a rabbit disease set off a chain of events. Myxomatosis, a South American rabbit virus, was released in Australia in 1950 and reached Britain in 1953. It killed about 99% of British rabbits. With no rabbits grazing, the grassland turf grew tall and the soil surface cooled.

A heat-loving red ant declined, and the large blue butterfly depended on that ant. Its caterpillars trick the ants into carrying them into their nests, where the caterpillars eat the ant grubs. The large blue became extinct in Britain in 1979. Brought back from Sweden from 1983 onward, it is now a celebrated conservation comeback.

Chemical pesticides fell out of favour after the American writer Rachel Carson published Silent Spring in 1962. Its title imagines a spring with no birdsong, and the book exposed how DDT and other pesticides were harming wildlife, especially birds. A landmark of the US environmental movement, it led to the Environmental Protection Agency in 1970 and the US ban on DDT in 1972. The ban boosted interest in biological alternatives, and US schoolchildren still learn how the bald eagle recovered after it.

Picture a young salmon hatching in a freshwater stream. Salmon are anadromous: born in fresh water, they migrate to the ocean to grow, then return years later to spawn. Pacific salmon die after spawning once, but Atlantic salmon can spawn more than once. North America’s five main Pacific species are chinook, also called king, coho, sockeye, pink and chum.

How do they find their way home? Young salmon imprint on, or lock into memory, the chemical “scent” of their home stream. Adults cross the ocean, possibly guided by Earth’s magnetic field, then follow that scent upstream. Arthur Hasler’s research in the 1950s explored this homing by smell.

Because most fish return home, each stream’s population, called a “run” or “stock”, adapts to local conditions. These include water temperature, migration distance and timing. Such varied populations steady the whole species, which is called the portfolio effect. It works like an investor who spreads savings across many different shares.

A classic warning about low diversity is the Irish potato famine of 1845–49. At that time Ireland relied largely on a single potato variety. Salmon face their own threats, summed up as the “four H’s”. These are habitat, hydropower dams, harvest, and hatcheries, the places where people breed fish.

From the early 1990s, many Pacific salmon populations were listed under the Endangered Species Act, the US law that protects species at risk. The agency in charge treats distinct salmon populations as units that it can protect separately. In 1992 a single sockeye, nicknamed “Lonesome Larry”, returned to Idaho’s Redfish Lake. The fish became a symbol of the decline.

Salmon are also central to the tribes of the Pacific Northwest (see Topic 2 for Native American history). In 1974 a court ruling, the Boldt decision, affirmed their treaty right to half the harvestable catch in Washington State. Salmon are the icon of the Pacific Northwest and Alaska, from Seattle’s fish-throwing Pike Place Market to Alaska’s Bristol Bay, the world’s largest sockeye run. Fights over dams and salmon are recurring news in the region.

Picture grassland dotted with millions of shallow wetlands, left behind by retreating Ice Age glaciers. This is the Prairie Pothole Region, which stretches across the Dakotas, Minnesota, Iowa, Montana and Canada’s prairie provinces. It produces around half or more of North America’s ducks. That is why it is called “America’s duck factory”.

Wildlife managers focus on ducks for a reason. Waterfowl, meaning ducks, geese and swans, are game birds, hunted for sport. Since 1934, US duck hunters have had to buy a federal “Duck Stamp”, and the money buys wetland habitat. A hunters’ group, Ducks Unlimited, also pays for conservation.

Songbirds are often an afterthought, even though grassland birds such as meadowlarks and bobolinks are among North America’s fastest-declining birds. Raccoons, striped skunks, red foxes, badgers, crows and magpies all take eggs and chicks. Smaller ground squirrels and mice raid small songbird nests too. Trapping predators in the nesting season is a real management tool, but a controversial one.

A food web is the network of who eats whom, and like a spider’s web, a tug on one strand can move others. Removing one predator can let its prey or its smaller competitors multiply. When mid-sized predators boom after larger ones are removed, ecologists call it mesopredator release.

Duck hunting is a major American tradition, and the yearly Federal Duck Stamp art contest is a well-known institution. Raccoons, jokingly called “trash pandas”, and skunks are familiar backyard animals across the US.

Think of carrots, tomatoes, mangoes, saffron and autumn leaves. Their yellow, orange and red colours come from carotenoids. Carrots owe their colour to beta-carotene, which the body turns into vitamin A. Only plants, algae, fungi and some microbes can make carotenoids, so animals must eat them.

Biologists call such colouring “diet-dependent”, and for these colours the saying “you are what you eat” comes true. Flamingos hatch grey-white and turn pink from the carotenoids in the algae and brine shrimp they eat. Zoos feed them supplements to keep them pink. Carotenoids also make salmon flesh pink and cooked shrimp red.

Male house finches range from pale yellow to bright red depending on their diet. In research in the 1990s, females preferred the redder males. The red of the northern cardinal and the orange spots of male guppies also come from carotenoids.

In 1871 Darwin described sexual selection: traits can evolve because they win mates, even if they cost survival. Darwin wrote that the sight of a peacock’s tail feather “makes me sick!”, because it was so hard to explain by survival alone. The peacock is, of course, India’s national bird.

Animal signals are colours, songs, scents and displays that pass information to other animals, such as rivals or possible mates. Bird song and the flashing of fireflies are other familiar examples.

In the US, the bright-red northern cardinal is the state bird of seven states, more than any other bird. It gives its name to sports teams such as the St. Louis Cardinals. The pink plastic lawn flamingo is a beloved piece of American kitsch, or lovably tacky decoration.