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which allowed the tropical ape that they were - and we are - to survive in a climate that killed off an animal more used to bad weather but less well clad. Perhaps Homo sapiens murdered the Neanderthals or starved them out, but we do not know. Sex was not on the agenda, for fossil DNA from a Croatian specimen shows that they were quite distinct from our direct ancestors. In addition, today’s Europeans and Middle Easterners retain no ancient lineages that might have come from an extinct relative. DNA suggests that the Neanderthals’ last common ancestor with modern humans lived in Africa more than six hundred thousand years ago, long before Homo sapiens emerged.
    Soon after the loss of his cousin, that species began to spread across the world. Modern humans filled the whole habitable globe no more than a thousand or so years before the present, when at last men and women reached New Zealand and Hawaii. Their ancient journeys can still be read in DNA. The double helix reveals a clear split between Africa and everywhere else, a legacy of the small group of migrants who first stepped out of our native continent into an uninhabited world, together with a second and more ancient split within Africa that separates the Khoi-San - the Bushmen - from all others. Other great genetic trends, such as those across the New World and the Pacific, track the last migrations into a deserted landscape.
    Once, it seemed that modern Europe had a more complicated history than did most of the globe, with several waves of migration superimposed on each other. The genes of local hunters, who arrived long ago, were - perhaps - diluted by those of the first farmers who spread, just a few thousand years before the present, from a population explosion in the Middle East. Some variants do show a trend from south-east to north-west, in a pattern that might indeed reflect a slow wave of inter-communal sex. The archaeology of pots and seeds suggests in contrast that agriculture was taken up at some speed, as soon as people learned about it, with no need for weddings. In Britain, at the western edge of the new technology, carbon dates taken from charred grains suggest that around 4000 BC farming replaced hunting within just a couple of centuries, too fast for any large-scale mixture of populations. There is no real evidence of a flood of lascivious rustics coming from the east. Instead, ancient Europe was more open to ideas than it was to genes. The trends seen today are the remnants of the first grand migration thirty thousand years before the emergence of agriculture, as humans arrived in an empty continent from the south and east. The mitochondrial DNA - the female lineages - found in the remains of a hunter-gatherer group in northern Spain look more or less the same as those of modern Spaniards in the same place, with no sign of mass immigration. Modern Europeans trace most of their heritage to the first wave of hunters. Since then, they - and their DNA - have tended to stay at home.
    As men and women filled the world they killed off many of their kin. The Neanderthals were the first to go, and human habits have not changed since then. Today, just a few remnants of our once extensive clan linger on. In a century or so we will be the single large primate (and almost the only large mammal), to be found outside farms or zoos. Almost all the apes will be gone, some before they are studied by science. That fact is a tragedy both for the creatures involved and for science itself, for each of them says something about our own biological heritage. They contain within their DNA the story of human evolution and, perhaps, more: for some of our own inborn diseases are caused by genes identical to some that function perfectly well in our relatives.
    The physical similarity of primates and humans was noticed by Queen Victoria and, after The Origin , was often used by those anxious to judge the evolutionary status of their fellow men. Charles Kingsley, author of The