WHEN CHARLES DARWIN MOVED TO DOWN HOUSE IN 1842 THE population of England was fifteen million and London, the largest city in the world, had two million inhabitants. At the time of his death, forty years later, the number of Londoners had doubled and the capital’s fringes were creeping towards his retreat. Its population has doubled again since then and Darwin’s house has become a museum. It sits in a carefully preserved enclave that pretends to be a village but is in fact part of the London Borough of Bromley. A few segments of nearby countryside have been preserved (the “tangled bank,” the microcosm of life referred to at the end of The Origin, is almost unaltered), but the landscape around Down House is now suburban at best. A glance across the famous Sand Walk reveals the tail fins of planes parked a few hundred yards away at Biggin Hill Airport, a Battle of Britain air base whose pilots claimed to have shot down more than a thousand enemy aircraft. Now it is the most popular light aviation centre in England, and its annual air fair attracts a hundred thousand visitors. A lot has changed in the Kentish countryside since Charles Darwin walked across what has become an oil-stained strip of tarmac.
Many other places associated with the great man—and many of his subjects, from apes to earthworms and from insectivorous plants to Homo sapiens himself—have also been transformed. That would be a surprise to the patriarch of Down House. Darwin looked at the past to understand the present. He scarcely considered what the future might bring, for in his view evolution was so slow, and flesh so stable, that no real changes in the world of nature would be visible for many generations. In the long term, no doubt, the outlook was bleak; as he wrote to a friend: “Even personal annihilation sinks in my mind into insignificance compared with the idea or rather I presume certainty of the sun some day cooling and we all freezing. To think of the progress of millions of years, with every continent swarming with good and enlightened men, all ending in this, and with probably no fresh start until this our planetary system has again been converted into red-hot gas. Sic transit gloria mundi, with a vengeance.”
A moment of hindsight two centuries on shows that he was too conservative in his predictions. Every continent is indeed swarming with men, a few of them enlightened, but progress (if such it is) has not been slow but meteoric. A lot has happened since 1809 and a lot more is about to take place. In the next two centuries, plants, animals, and people will see an evolutionary upheaval greater than anything experienced for thousands of years. Now, the prospect of biological annihilation is far closer than is the certainty of the heat death of the universe.
In the last few weeks of his voyage, in July 1836, the young explorer had a brief vision of what lay ahead. The Beagle dropped anchor at Saint Helena, halfway between Africa and South America. The island, first occupied by the Portuguese in the sixteenth century, is one of the most isolated places in the world. Darwin was delighted by it: fifty square miles of volcanic mountain rose “like a huge black castle from the ocean.” He admired the “English, or rather Welsh, character of the scenery” and noted with surprise that Saint Helena’s vegetation, too, had a British air, with gorse, blackberries, willows, and other imports, supplemented by a variety of Australian species. Over seven hundred plants had been described—but nine out of ten were invaders. They had driven the original inhabitants to extinction or to refuges high in the mountains. A sweep of thin pasture near the coast was known to locals as the “Great Wood”—which is what it had been until the previous century, when the trees were felled and herds of goats and hogs consumed their seedlings and killed the forest. Plagues of rats and cats had come and gone as they ate themselves to extinction. On his first day ashore, he found the dead shells of nine species of “land-shells of a very peculiar form” (one of the few mentions of snails in his entire oeuvre) and—in an early hint of evolution—noted that specimens of one kind “differ as a marked variety” from others of the same species a few miles away. All but one of those molluscs had been wiped out and replaced by the common brown snail of English gardens.
Almost two centuries after his visit, life on Saint Helena is worse. The island then had forty-nine unique species of flowering plant and thirteen of fern. Seven have been driven to extinction since the arrival of the Portuguese, two survive in cultivation, and many more are on the edge. The last Saint Helena olive died of a fungal disease in 1994. Of the tree-fern forest of the high mountains—still in robust health at the time of the Beagle—a few parts remain, but other unique habitats Darwin visited, such as the dry gumwood, have gone. Of the ebony thickets just two bushes are left. The island’s giant earwig (at six inches the world’s largest), its giant ground beetle, and the Saint Helena dragonfly, all common in the 1830s, have not been seen for years, and the snail of peculiar form is now reduced to a population of no more than a few hundred. The Saint Helena petrel is extinct, and just one endemic feathered creature, the wire bird, is left—but that too is under threat.
Three months after the farewell to Saint Helena, the young explorer wrote in his diary that “we made the shores of England; and at Falmouth I left the Beagle, having lived on board the good little vessel nearly five years.” His account of the expedition ends with a spirited enjoinder to all naturalists “to take all chances and to start on travels by land if possible, if otherwise on a long voyage.” Charles Darwin never left British shores again.
He had no need to, for, as this book has shown, the plain landscapes of his own country gave him the raw material for a life filled with science. Darwin’s fifty years of work on his native land’s worms, hops, dogs, and barnacles changed biology forever. Since then the British Isles have provided another useful lesson for students of Nature, for that modest archipelago is a microcosm of the global upheavals that have taken place since the great naturalist came home.
Bartholomew’s Gazetteer, in its edition just after Darwin’s death, describes Kent, “the Garden of England,” as a paradise: “The soil is varied and highly cultivated. … All classes of cereals and root produce are abundant, as is also fruit of choice quality and more hops are grown in Kent than in all the rest of England. The woods are extensive. … Fishing is extensively prosecuted … of which the oyster beds are especially famous.”
A lot has changed. Kentish farms bring in half what they did even a decade ago. The oysters are almost gone, and the salmon fishery of the Thames, which fed the apprentices of London with such abundance that they refused to eat fish more than once a week, has collapsed. Bucolic pursuits have been replaced by that invaluable product, “services,” which accounts for three-quarters of the county’s contribution to the nation’s wealth. Kent is a dormitory of London, and London has become a staging post for the world. The flow of people, power, and cash has carved up the county’s landscape with motorways, rail links, and webs of power lines. The oasthouses that once stored hops have become commuter homes, and the hops themselves—the raw material of groundbreaking experiments on plant movement—cover a fraction of the fields Darwin knew. Although the Great Wen has been kept partly at bay by the Green Belt, plans for a “Thames Gateway” mean that yet more of the Garden of England will soon be a bland suburb.
Much of his work on insect-eating plants, self-fertilisation, and orchids took place in Ashdown Forest in the adjacent county of Sussex, where his cousin Sarah Wedgwood had a house and where he often walked, mused, and botanised. A visit today shows how fast the wild can retreat. In Victorian times the Forest was one of several vast belts of English heath, successors of ancient tracts of trees felled thousands of years ago (Cobbett called it “the most villainously ugly spot I ever saw”). Ashdown was used by the Normans as a game preserve, closed off with a twenty-mile bank. In time most of the trees were cleared and burned (in iron foundries as much as hearths), and it turned into heathland, a seminatural part of the seminatural landscape that is England. Since The Origin, the nation has lost nine-tenths of its heaths. The Forest, at a thousand acres, is the largest piece left, but even that is a shadow of what it was. The acid grasslands and marshes have been taken over by bracken or have dried out as water has been pumped away to slake the thirst of millions. Many once abundant species—gentians, asphodels, sundews, orchids, and more—are now rare, and some of the great man’s walks have become suburbs, farms, or golf courses.
The Common Plants Survey keeps count of sixty-five of Britain’s most abundant flowers, from primroses to bluebells and foxgloves, in five hundred random plots scattered across the country. A century ago those species were almost everywhere. By 2007, a quarter of the sites had none of them. Most of the empty plots were in huge fields of corn or on wide pastures without hedgerows. Others were in woodland. England’s forests—albeit preserved by the Woodland Trust, the Royal Society for the Protection of Birds, and the National Trust—have lost much of their diversity. A stable ecology maintained by the labours of woodmen has been replaced by museums of elderly trees in which bluebells and foxgloves, and sparrows, cuckoos, and jackdaws, are in decline. Across England—and across Europe and North America—the fields are starved of life. Subsidies have made a desert and called it farming.
Kent’s sorry tale is repeated in many of Darwin’s favourite places, from Stonehenge to Shrewsbury and from Wales to the Highlands. In a further blow to the products of evolution, the world has come to Kent, and its animals—and people—have migrated to the world. His home has been united with the rest of the planet, which has become a single giant continent—a global island—rather than an archipelago, real or metaphorical. Humankind, too, has been homogenised, and even genteel Bromley now has a tenth of its citizens from an ethnic minority. No longer does evolution mould the natives of each corner of Earth to fit their own domain. The struggle to exist for both man and beasts has become a worldwide conflict rather than a series of local skirmishes. Some creatures thrive in the international arena, but many more are doomed.
Evolution generates difference. One species and one alone has put the process into reverse. Man has instituted a simplification almost as great as that brought by the explosion that destroyed the dinosaurs. The Galapagos themselves are a stark reminder of what he has done. HMS Beagle visited the island of James in 1835. Food was plentiful: “We lived entirely on tortoise meat … the young tortoises make excellent soup.” In those ungainly creatures, Darwin saw, without realising it, his first hint of evolution, for the animals from that island were distinct from those on nearby Indefatigable and Albemarle. In a rare conjunction of taxonomy with gastronomy he noted that the James specimens were “rounder, blacker and had a better taste when cooked”—which at the time seemed little more than a curiosity but was in fact an introduction to the biology of change.
Now, the tortoises of James and its fellows are almost extinct. From a quarter of a million in the Beagle’s day, their numbers have dropped to fifteen thousand. Three of the fourteen unique races have gone, and just one animal, the famous Lonesome George, is left from another (at the age of ninety or so, he was twice persuaded to mate with a female from a different island, but on both occasions the eggs were sterile). Pigs, as much as men, have killed off the tortoises, for they love to feast on their eggs. Goats have blighted many islands. Less obvious pests have also made their way to the archipelago. The cotton cushiony scale insect invaded twenty years ago and has reached across the whole of the Galapagos, attacking dozens of kinds of native plants.
Pigs and scale insects are dangerous because they have epicurean tastes. They are happy to try anything once; and—like the young explorer with the tortoises—will turn to a novel foodstuff if their usual diet is not available. They can hence snack on the last specimens of an endangered species without eating themselves out of house and home. Such generalised predators, as they are called, are a real threat. On the Galapagos, cats are a plague, pigeons have pushed out their feathered relatives, and alien wasps have done terrible damage to the insects. The islands face an era in which specialists, evolved to fit their own small place in nature, are falling to loutish strangers able to cope more or less anywhere. A tourist on the islands today (and a hundred and fifty thousand arrive each year) has less to admire than did the crew of the Beagle. Next century’s visitors may find the place more or less indistinguishable from South America. The products of millions of years of isolation have been destroyed by man, the most generalised predator of all.
The Galapagos are the icons of evolution and their problems get plenty of attention. Many other oceanic islets—rare, specialised, and fragile as their natives are—face the same cataclysm or worse, but not many people notice. From Saint Helena to Tahiti and from Hawaii to the Cape Verdes, the alarm has at last been raised. It is too late to save such places, most of which began their decline long before the Beagle arrived.
The fate of the giant earwig of Saint Helena and the tortoises of the Galapagos is sad enough, but Darwin’s more modest subjects provide an equally trenchant statement of the universal attack on the biosphere. They are both under threat and a threat to others. Those humble creatures—the earthworms and bees, the primroses and orchids, the plants that climb and those that kill their prey—all face an ecological earthquake. The lessons they bring are more alarming than are those from the distant isles of the Pacific, for they show that the crisis has moved beyond the exotic to the familiar, and how what was commonplace is becoming rare.
The sundews of Kent and Sussex are far from safe, and many insectivores sent to Down House from around the globe are in deeper trouble. The wide fields of Venus flytraps and pitcher plants that covered parts of the Carolinas have been destroyed. Agriculture and drainage tear up their habitat, and the gardeners who dig them up do not help. A more subtle threat comes from fire control, because such beings thrive best in places often burned—which in today’s carefully managed countryside happens less than it once did.
Darwin’s other subjects, the orchids, face the same problems. Their enemies are those of the insectivores: aggressive farmers, fragile habitats, and greedy collectors. A third of the fifty British species are under threat, and several have populations of fewer than a hundred—and one, the lady’s slipper orchid, was for a time reduced to a single individual in the Yorkshire wilds (thousands of greenhouse specimens have now been sown in the hope of rescuing it). The Victorians suffered from “Orchidelirium,” and paid large sums for rare specimens. Traders destroyed whole beds to ensure that their own stock kept its price. A decade after The Origin the botanist Joseph Hooker noted how the area around Rio de Janeiro, visited by the naturalist on the Beagle thirty years earlier, had been pillaged of its orchids, which have never come back. Unlike the Dutch tulip fever of the seventeenth century the orchid mania is still upon us, with a global trade worth ten billion dollars a year. Expensive specimens sell for thousands. Much of the business is legitimate, and the plants are cultivated or cloned in huge numbers from cells taken from single individuals. Plenty more is not; and many wild species from Thailand, China, Brazil, Guatemala, and elsewhere are at risk. About one species in ten is threatened, and the continued loss of tropical forests means that many more will disappear before they are known to science. Even those on “Orchis Bank,” near Down House, survive only because of the vigilance of local naturalists.
The losers in the post-Victorian battle are being replaced by others that thrive in the new global economy. Many have migrated to new lands, where they cause havoc. Weedy plants may be a nuisance, but weedy animals are worse.
Britain itself faces a revenge of the immigrants: a wave of creatures that have appeared from almost nowhere. A New Zealand flatworm introduced to Belfast in the 1960s has run wild (and an Australian cousin has also begun to move). It wraps itself around earthworms and digests them alive. The pest has spread through Scotland, northern England, and Ireland, and in some places worm populations have collapsed.
Modern society has been built upon aliens, creatures moved from their native lands, be they maize, chickens, or cattle. They evolved in the Middle East, in Asia, or in the New World but have been transported to all parts of the globe. Many have become pests in their new homes, and many more have hitched rides with those who cultivate them. Darwin noticed the invasion of British plants into the United States and asked his American colleague Asa Gray, “Does it not hurt your Yankee pride that we thrash you so confoundedly?” The New World soon got its own back, with grey squirrels that eat woodland birds’ eggs and Canadian pond weed that blocks streams. The third millennium is the era of weeds, and the weediest species of all—Homo sapiens—is to blame.
Plenty of weeds stay at home; they live in disturbed ground, flourish for a short time, and move on to a new patch when conditions change. They do little damage except to the good temper of gardeners. When they escape, they become the botanical equivalents of pigs: they move in, exploit what is available, and destroy the locals. Many imports from the Old World have thrived in the Americas. One European roadside species, the knapweed, a small thistle with a pink or yellow flower, has covered millions of hectares. It secretes a poison that kills native plants, which—unlike those at home—have not evolved resistance. As a sinister side effect it also poisons horses. The knapweed is now out of control. Others, such as the Brazilian water hyacinth introduced to Caribbean islands, find themselves in a place without their native pollinators, take up self-fertilisation, and become a fecund pest. Some even hybridise with a relative, hijack its genes, and gain renewed virulence as a result. The bright yellow and poisonous Oxford ragwort, common in disturbed ground in England, is a hybrid of two Sicilian species brought to the Oxford Botanic Garden in the seventeenth century, which escaped and mated with each other. The new plant is still spreading.
Some of the most aggressive aliens are the climbers. Even the hop has become a nuisance, with a Japanese variety spreading across the United States. Kudzu, a climbing pea, is also native to Japan. It was transplanted into that nation’s ornamental garden at the 1876 Philadelphia Exposition. Gardeners liked the flowers and it was dispersed across the country. At first sight, the immigrant seemed helpful. It lays down roots two metres long and in the South was used to reduce soil loss after forests had been cut down. Railroads gave free kudzu to farmers in the hope that they would cultivate it for fodder that their company’s trucks could then transport. That was a mistake. The weed grows so fast that the locals recommend, tongue in cheek, that windows be closed at night to keep it out. In some places it extends by thirty centimetres a day—twenty metres and more a season—and can soon smother a huge tree. Kudzu is out of control over an area that straddles Alabama, Georgia, and Mississippi and has spread as far north as Massachusetts and as far west as Texas. Attempts to subdue it cost half a billion dollars a year.
Other climbers are just as busy. Florida has “air potatoes,” yams from West Africa that sprawl over trees and block the light. It also suffers infestations of climbing ferns from Asia. English ivy has shaded out tracts of maple forest around Seattle. In Australia the humble blackberry is a nuisance, as is the mile-a-minute vine, a morning glory introduced from the Old World tropics. Most are harmless at home, but a lifestyle that depends on a burst of growth when a sudden open space appears in the forest is lethal when exported to a place not adapted to their wiles.
Some of the climbers’ success emerges from another by-product of human activity. The effects of the carbon crisis on climate are familiar enough—but climbers thrive in the new and enriched atmosphere. Over the past two decades the proportion of the Amazon jungle taken up by lianas has rocketed up, in part because the forest has been partly cleared by loggers, but also because of the increased carbon dioxide, which they can soak up and lay down as wood. As a result they flourish at the expense of trees. Ivy, too, now grows at an exceptional rate as it gains extra carbon from the air.
Plenty more of Down House’s experimental subjects have found a new home. Even barnacles are a menace. Some, helped by the spread of shipping and by water (larvae included) dumped from ballast tanks, have begun to gallop around the globe. A barnacle the size of a tennis ball, once restricted to the Pacific coast of South America, has within the past five years made its way to Florida, Georgia, and South Carolina. It infuriates boat owners as it acts as an unwelcome brake on their vessels’ smooth bottoms. A species common on the coasts of California and Oregon has, in return, spread in huge numbers to Argentina. It was first recorded in the 1970s and has taken over the shoreline for more than a thousand miles. The animal has driven local sea snails, seaweeds, and more to extinction. It has found its way to Japan and at the present rate will soon reach Chile and wipe out the creature that drew the young Darwin’s attention to the joys of the barnacle in the first place.
On land, too, a revolution is under way. The worm has turned. Much of the northernmost part of the Americas is almost devoid of native earthworms. They were wiped out by the last Ice Age, which left just a few remnants in the Pacific Northwest and in a few patches elsewhere. Native Americans may deplore what the white man brought, but they did at least import earthworms, carried in pots or on the mud of immigrants’ boots. Now fifty and more exotics have arrived. They can advance several metres a year as they burrow, and even faster when they hitch a ride. Escapes from bait tins take them far into remote forests as anglers search for new lakes.
Unlike most invaders, they have been of some use. The West was won with the help of worms. Before the white man arrived, the northern prairies fed no more than herds of buffalo, but as the aliens spread, their fertility soared and maize and cattle moved in. Millions of acres were turned over, and a dense and surly coat of acidic humus that sat on top of a sterile mineral layer was transformed into a well-mixed light soil just right for farming.
Not all the news was good. Before these immigrants put in their appearance, many northern states and much of Canada were covered by fern-filled forests that sprang from deep mounds of leaf litter, or duff, which mouldered over years rather than being dragged into the ground by annelids. The duff sheltered beetles, salamanders, mice, and more. The worms ate it, leaving a naked and unprotected surface. Most of the natives evolved to deal with undisturbed ground and suffer as a result. Thick undergrowth gives way to horsetails and pitcher plants. The local vegetation also depends on a relationship with the fungi that cluster around their roots—and they too have been lost under the assault. Aspen and birch trees die, forests of sugar maple are parched as the water runs through the newly permeable ground, and prairie herbs disappear and are replaced by their European equivalents. In northern Minnesota, great tracts of hardwood have been destroyed in the past forty years, and the problem is spreading. The once ponderous economy of those ancient forests has speeded up, and vast quantities of carbon and nitrogen have been washed away. The problem is not limited to North America, for exotic worms have also invaded tropical jungles. What they will do, we do not yet know.
Insects, too, followed the farmers and some, like the worms, are a help. Most North American bees came from Europe. They arrived within two years of the Pilgrim Fathers, brought in by sweet-toothed pioneers anxious for honey. At once the immigrants set up wild colonies and thrived. So much were they an indication of European settlement that the Indians called them the “white man’s fly.” A wave of bees moved up the valley of the Missouri at forty miles a year, and, it was said, as the bee advanced, the buffalo retreated. So impressed were the Mormons of Utah by the animal’s hard work that they chose it as their state symbol.
European bees still number in the billions in North America. Like the underground invaders they have driven out local species and like them they play a large part in the agricultural economy. Many crops—fruit trees above all—need pollinators if they are to thrive. In fact, 80 percent of the top hundred or so food plants, responsible for two-thirds of global production, depend on them. California has so many almond, cherry, and apple orchards that natural pollinators are unable to keep up, and a healthy hundred-and-fifty-million-dollar annual honeybee rental industry has grown up. As the season moves on, the hives follow the flowers. Without European bees the yield of fruit, seeds, and nuts in the United States would drop by nine-tenths. The aliens may have damaged their local relatives, but they have done a lot to help the people who brought them.
On both sides of the Atlantic bees are in decline. The numbers of wild colonies of European bees in parts of North America are a tenth, and of those in hives a third, of what they were half a century ago. Insecticides, air pollution, mite parasites, viral disease, and competition from introduced African bees have been blamed for the crisis, as have the loss of hedgerows and other scrubby places which were a home for useful insects. In spite of attempts to keep the pollinators happy with wild flowers planted around orchids and by controlling insecticide use, the decline goes on. In an airborne twist to the tale, pollution kills the scent of many flowers and further reduces the chance that an insect will find its target. That news is bad for honey lovers, worse for farmers, and may be catastrophic for many native plants.
The troubles of the bees, the spread of weeds, and the destruction of the soil are just part of a global crisis of agriculture. The population boom and the increased prices of oil and fertilisers are also to blame. After a period of stability or even decline, the price of wheat, rice, chickpeas, and other staples has gone up. The era of plenty may be near its end. India, long an exporter of food, has begun to import rice. The population explosion in Africa has led to shortage, and although Chinese numbers are under better control, affluence means a shift from cheap grains to expensive beef. World production of meat has gone up fourfold since the 1960s. A carnivorous diet is expensive in many ways. It takes fifty times more energy to make a pound of beef than a pound of corn. The world’s fisheries have been depleted, and—in a fatuous gesture of ecological concern—some of its finest land is now used to grow biofuels. As the climate changes, productive regions have lost their worth. Gloom is an occupational hazard for ecologists, but it is getting harder to be cheerful.
The fate of Charles Darwin’s experimental subjects is part of a larger litany of decline. The Red List of Threatened Species includes sixteen thousand names, and every year some spectacular creature is declared to be extinct. Many more pass unremarked and unmourned. If weeds and crops are to spread, others must pay the price. Most disappear as their habitats are destroyed. Almost half the rain forest has gone, and mangrove swamps and Mediterranean landscapes face the same disaster with less publicity. Extinction is part of evolution. Around half a million bird species have lived since the group evolved a hundred million years ago, but only about ten thousand lived at any one time—and that is the figure today (although twelve hundred among them are threatened). Even so, it is hard to deny that we live in a time of rapid change, in which some creatures thrive while many more are doomed.
One small and specialised group of mammals—until not long ago a vigorous part of the fauna of Europe, Africa, and Asia—is under particular threat. A world once filled with our hairy relatives will soon be a Planet of the Ape. Almost half the world’s six hundred or so varieties of monkeys and apes face disaster. Habitat destruction is the main threat, although hunters and disease also kill them off. Every large primate except one is close to the end of its evolutionary road. Just two hundred thousand chimps are left in the wild. Gorillas have gone even faster and in some places have died in multitudes from Ebola virus, caught from humans. Many populations of the orangutan, broken up as the forest is destroyed, are already too small to sustain themselves.
The genes show that the great apes have suffered a real reversal over the past several hundred thousand years. The amount of variation in DNA says a lot about the abundance of creatures in ancient times, for populations that stay small for many generations lose genetic variability through the accidents of reproduction, while abundant animals can maintain a pool of diversity that persists for long after any collapse in numbers. The double helix hints that for much of that period orangs, chimps, and gorillas flourished while Homo sapiens and his immediate ancestors struggled to survive. Chimps, threatened as they now may be, are three times more different, one from the other, at the molecular level than are humans. Even within the past seventy thousand years, Homo sapiens went through a bottleneck of just two or three thousand individuals during a long age of drought (and there have been plenty of local crises since then as humans filled new continents and remote islands). For much of history we were the endangered primate while our relatives boomed. Now the boot is on the other foot.
The world has six billion people (and the figure will rise by half when the population peaks, at around the time of The Origin’s bicentennial). Homo sapiens has, like the kudzu vine and the earthworm, begun to multiply and to move. By so doing it has revolutionised its own future. Although we may not notice it, our biology is in the middle of a shift as great as that of many of the animals and plants that surround us.
Evolution occurs in space as much as in time. As Darwin saw on the Galapagos—and as is manifest in the geography of human genes—populations isolated from each other diverge, either in response to local forces of natural selection or by random change. Genetic trends have also emerged over the past few thousand years because of accidents of settlement, with reduced levels of variation in recently discovered places such as the New World or the far Pacific. In the same way, ancient patterns arising from the migration of peoples from the Levant to the British Isles have been preserved. Now that history is being lost. We have long been the weediest primate of all but we are becoming weedier still. History has always been made in bed, but the beds are closer together than ever.
Inbreeding, in the developed world at least, is less common than it was. How far was your birthplace from that of your partner, and how far apart were those of your mother and father, and your grandmother and grandfather on each side? For almost everyone the distance has increased over the generations and continues to do so (my wife and I first saw the light three thousand miles apart, my mother and father about three; as my students say, it shows). Even in the Middle East—that centre of sexual conservatism—education, affluence, and the chance to travel mean that DNA is on the move. A series of Israeli Arab villages experienced a drop in the incidence of cousin marriages from about one in four in the 1980s to one in six at the millennium. The same is true in Jordan, Lebanon, and Palestine.
In the past, hurdles in the mind kept people apart. If today’s remnants of hunting tribes are any guide, any attempt to join another group was punished by death. European frontiers, too, are marked by genetic steps (with a deeper difference in identity between the beer drinkers of the north and the wine bibbers of Spain and Italy). The continent’s long history of staying close to home is manifest in its surnames—those windows into sexual history—as much as its genes. A family tree of names used to fit almost exactly with national boundaries, with the Camerons more or less confined to Scotland and the Zapateros to Spain. Spain itself has the most localised patterns (and can also boast the commonest surname in Europe—Garcia), while in both names and genes Paris is the most diverse city in Europe.
Names—and the DNA that accompanies them—are on the move. In 1881, Darwin’s last full year (and the date of a British census), his surname was borne by about one Briton in fifty thousand. Its origin is Welsh, from “derwen,” or oak: a name transferred to the River Darwen in Lancashire. In his day its headquarters was in the Sheffield region, where the Darwin tag was eight times more common than in Britain as a whole. Nearly all those who bore it lived within fifty miles of the city (the Joneses—the group with the second most common British surname after Smith—were still, in those happy days, largely confined to Wales, where in some villages they formed a majority). By 1998, the naturalist’s name had spread northward to find a new centre in Durham, with secondary nuclei across the north from the Mersey to the Tyne and a minor outbreak in Herefordshire. The Joneses too had migrated, with a great smear across the Welsh borders into northwest England and as far south as London. No longer must a Darwin, a Jones, or anyone else marry someone from their own family for lack of choice. Instead they come into contact with a diversity of potential partners. The proportion of shared names in the marriage records of a typical English village has gone down by 1 or 2 percent a year even since the mid-1970s and by much more since the publication of The Origin of Species. Sheffield, once its author’s nominal capital, now has scores of new names from across the world.
The United States has gone even further down the road to homogeneity. Its telephone directories contain a million different surnames. Some remnants of history remain, with Wisconsin full of Scandinavians while the phone books of New Mexico, Colorado, and Texas reveal the presence of many Spanish immigrants. The general picture, though, is—unlike Europe’s—one of geographic uniformity. One in eight Americans is foreign-born (in California the number is twice as many), and Americans move house, on average, a dozen times during their lifetimes, with ten million each year shifting from one state to another. Such frantic migration soon mixes up names and, in time, genes. That shift—the train or plane as an agent of evolution—is spreading around the globe and will soon even out yet more of man’s genetic differences.
Almost everywhere, the biological frontiers are becoming porous. An era of homogeneity is at hand as thousands of people move in search of work or sunshine and, in the end, sex. In Britain, the proportion of those born abroad has doubled in the past fifty years and now represents a tenth of the population. Man, like the ecosystem he lives in, is in the midst of a grand averaging.
Intermarriage has been around for a long time. Many white Britons can trace at least one black ancestor from the small African population that lived in England several centuries ago. About half the men of a certain Yorkshire family, the Revises, share a Y chromosome type otherwise found only in West Africa. There have been Africans in Britain since Roman times, and by the eighteenth century these islands held ten thousand black people. Since then the proportion of Britons who claim recent full or partial descent from Africa has gone up by a factor of twenty. The popular view of the British as a nation walled into a series of ghettos is wrong. In 1991 ethnic minorities in one in ten electoral wards (a ward is the smallest parliamentary subdivision, with around eight thousand wards in England) constituted more than 10 percent of the total citizenry. Ten years later the figure was one in eight, and in 2011 it is expected to be one in five. Most of the growth comes not from immigration but from the movement of people within Britain and from the simple fact that young people, many of them migrants, have more children than do older individuals.
All geneticists are firm believers in the power of lust to overcome social or geographic barriers. In 2001, about one British marriage in fifty—a quarter of a million in all, with many more couples cohabiting—was between partners of different ethnic groups. Hundreds of thousands of children have one parent from Britain and one from the Caribbean, and almost as many are the progeny of white and Asian parents. British Afro-Caribbean males are one and a half times more likely to marry a white woman than black women are to find a white husband (although those preferences are reversed for the Chinese). Such relationships are not, as often believed, found only among the poor, for more than half of those involved live in the suburbs and are richer and more educated than the national average. Assimilation is well under way in modern Britain, one of the most sexually open nations in the world. In today’s England, mate choice is influenced as much by level of education as by skin colour. Many other countries, whether they like it or not, are also opening up their gene pools. Homo sapiens—already the most geographically tedious of all mammals—will soon, like the worms and the insects, be even more uniform than he was.
In his global coalescence the shaven ape has evolved in much the same fashion as have weedy plants and animals. In other ways, though, man is unique: he is the only animal that has escaped—or almost escaped—Darwin’s unforgiving laws of life and death. Natural selection has long been at work on our species, even if our ingenuity has mitigated its power. Now, in the nation in which the idea was invented—and, more and more, in the world as a whole—natural selection has slowed down and may soon stop.
I depress my first-year students with the statement that two out of three of them will die for reasons connected to the genes they carry (a vague claim, but good enough to make my point). Then I try to cheer them up by pointing out that had I given the lecture in Shakespeare’s time, two out of three of them would, at age eighteen or so, be dead already. Even in the year of Darwin’s birth, about half of all British newborns died before they reached maturity. Life has seen a great change for the better. An English baby born in the year of the millennium had a 99 percent chance of surviving until 2021, and that figure continues to improve. Japan does even better, and the United States rather worse, but most of the developed world has seen a revolution in the prospects of the young. In most countries, even relatively poor ones like Ecuador, the death rate of children is no more than twice the British figure. In some places it is less. Africa is, alas, a great exception. The death rate for children under five is one in four in Sierra Leone and almost as high in Angola and Liberia, while Swaziland has an overall life expectancy of just forty years, half that of Japan. Differences in childhood mortality thus still account for most of the world’s variation in life expectancy, but outside the continent where our species began, those differences have withered away.
Natural selection exerts much of its power through the death of young people, for they have not yet passed on their genes. The death of the elderly—those over forty or so—is a less potent agency, for their sexual lives are more or less over and their relevance to evolution at an end. As a result, the great agent of change has lost much of its fuel. For most of history, the Grim Reaper was the master of man’s biological fate. Now he is taking a rest, and inherited differences in the ability to withstand cold, starvation, vitamin deficiency, or infectious disease no longer drive the evolutionary machine. Plenty of people still die for those reasons, but they do so after selection loses interest in them.
The Darwinian examination has two parts. In the developed world, most people pass the first: they stay alive until they are old enough to have children. The second section is just as inexorable but has a wider range of marks: any candidate for evolutionary success has to find a mate and reproduce. The more children they have, the better the prospects for their genes.
Among mammals, females are limited in the number of offspring they can produce by the mechanics of pregnancy and child care, while males are free to spread their sperm to many partners (although a certain amount of persuasion may be needed). As a result, males compete for the attention of females, while females must decide which males should be allowed in. Sexual selection turns on the same logic as natural selection: it depends on inherited differences, not in the chances of life or death but in the number of young. The rule applies as much to humans as it does to birds and flowers.
Both humans and peacocks have more variation in male sexual success than in female. Until not long ago, many societies contained a few satisfied libertines, outnumbered by a mass of sexually frustrated men. The powerful have always taken their amatory chances when they arise. Henry VIII was a minor player in the marital stakes. The Emperor in the Ch’I dynasty of China maintained a palace with several thousand women available for his amusement, while in tribal societies men with high status still have many more mates than their lowly (and often celibate) fellows. Mohamed bin Laden, father of Osama, had twenty-two wives and fifty-three children (and in the year of Osama’s birth he had six). His best-known son had, last time they were counted, five wives and twenty-two children. Given the equal numbers of men and women at birth, plenty of his henchmen will be obliged to die, naturally or otherwise, entirely childless.
The British Isles themselves have a history of sexual inequality that makes the antics of the founder of the Church of England look feeble. The evidence is in the Y chromosome, which marks male descent. It comes in a great diversity of form. In most places most men have their own more or less unique model. A fifth of the men of northwest Ireland, in contrast, share a more or less identical version of the Y chromosome—which means that they all trace ancestry from the same male.
Old Erin was rife with sexual inequality. Lord Turlough O’Donnell, who died in 1423, had eighteen sons and fifty-nine grandsons. He was himself a descendant of the High Kings of Ireland, all of whom claimed a single fifth century warlord, Niall of the Nine Hostages, as their shared ancestor. The Y chromosome of Niall the hostage taker has, thanks to his exploits and those of his descendants, spread to one in twelve of today’s Irishmen in Ireland and to millions more across the globe. The surnames fit too, for men of the Gallagher, O’Neill, and Quinn families (all of whom claim descent from the High Kings) are most likely to bear the special Y chromosome. In Ireland, for many centuries, the mightiest male passed on his genes, and many of his fellows passed their days in glum celibacy, occupying themselves as soldiers or priests instead.
Today’s reproductive universe is quite different. Everywhere the weak and the powerful—the poor and the rich—are sexually closer than they were. In almost every social class, the average number of children has, thanks to technology, gone down. Natural selection cares naught for that, for the important figure is not the number of offspring but the variation in how many progeny people have. That figure has shrunk. Five centuries ago in Florence, the upper crust had twice as many offspring as did the peasantry, but now the Florentine poor have slightly more than the rich; Britain is the same (which worries the right-wing press). The gulf has closed through restraint by the affluent rather than excess by the poor. A furtive exchange of contraceptive information meant that rich families became smaller while those of the poor stayed the same but now both groups are able to control the number of children they have. Schools too are a powerful agent of birth control. Everywhere, people with degrees have fewer offspring than those who drop out early. As education spreads, the fertility imbalances will become smaller still.
Inequality, in survival or in sex, is the raw material of evolution. The differences in people’s ability to stay alive and have children can be combined in a single measure that shows just how much of it is still available to evolution. Around the world, that figure—the “opportunity for selection”—is in decline. India tells the tale within a single country. The nation encompasses a range of cultures, from tribal hill peoples to affluent urbanites, together with vast numbers of peasant farmers whose lives resemble those of Europeans a few centuries ago. The figures of life, death, and birth, when put together, show that natural selection has lost nine-tenths of its power in India’s middle class when compared with its tribal peoples. Much the same is true when we compare the modern world with that of the Middle Ages and—to a lesser degree—even with that of the Victorians.
As Charles Darwin insisted, evolution is not a predictive science. Natural selection has no inbuilt tendency to improve matters (or to make them worse). For Homo sapiens, some nasty surprises no doubt lurk around the corner. One day, his machine will take its revenge, and we may well fail in the struggle for existence against ourselves, the biggest ecological challenge of all.
Whatever the future holds, two centuries after Darwin’s birth we have entered a new era in biology. The changes are not limited to the rain forest, the coral reefs, or the teeming tropics but are hard at work in Charles Darwin’s homeland and throughout the world. From Shrewsbury to the Galapagos, and from worms to barnacles to human beings, there has been a triumph of the average. The Earth as an island rather than an archipelago is a far less interesting place than when HMS Beagle set sail. Whether it becomes even less so—and whether it survives at all—depends on the talents of the only creature ever to step beyond the limits of Darwin’s theory and to be capable of concern about the future.