A hippopotamus herd in Trafalgar Square

Abstract

I have the dubious privilege of living in Camden Town, in central London. It's a place of living fossils, quite a few among them pickled in alcohol but most of the others the endangered (and Mohican-bedecked) survivors of the Sex Pistols Epoch. Should a Cro-Magnon Man, an Early Modern human from some 40 000 years ago, come and sit next to me on the Tube, I would probably not notice: he might be dressed in furs, covered in mud, and grunting, but in Camden that is pretty much par for the course. A Neanderthal might get a brief glance from fellow passengers, but the earliest known Briton from around 800 000 years before the present would probably find an empty seat on either side of him. And that's a bit strange, because in terms of physical appearance there has not been that much change in our fellow citizens over that period. Britain: One Million Years of the Human Story, a new exhibition in the Natural History Museum in London, makes that clear. A million-year-old skull looks not very different to the untutored eye from one that is 50 000 years old, although the former gets the label Homo antecessor and the latter H neanderthalis. In between, in terms of age, are skulls christened H heidelbergensis, while H sapiens emerged in Africa no more than 100 000 years ago. What makes us human is, in part, our sense of connection to the past. Some of its relics—like the skulls in this exhibition—are tangible, while others give a more subtle tie to days long gone. Perhaps the most remarkable on show are the 850 000-year-old human footprints—the oldest outside Africa—found in 2013 in the mud of coastal Norfolk and exposed when storms washed away the sand that had covered them. They seemed to have been a family group, and push back the date of the first known Briton by 300 000 years. Then the sea rose and the Continent was cut off, leaving Britain uninhabited, to inaugurate the great NIMBY Era, the 120 centuries when there was simply nobody around to spoil the view (and, for that matter, nobody to look at it either). Herds of hippos were free to roam in Trafalgar Square unmolested, leaving their teeth for the curious exhibition visitor to admire (now there's an idea for the next occupant of the Fourth Plinth). That idyllic epoch ended 60 000 years ago, and the Neanderthals—who occupied much of the Northern Old World—were free to invade when the sea fell back to leave a bridge to Europe. They were joined by modern humans from Africa who, quite soon, drove them out. The colonists set a familiar precedent by imposing their sexual needs on indigenous people. In South Africa, the “Cape Coloureds” trace their roots to the 17th-century arrival of the Dutch. The local Khoisan fought back against the colonists, almost all male, who killed or pushed out most indigenous men, and also brought in male slaves from the North. Khoisan women faced much pressure to enter into relationships with foreigners, but there was almost no sex between Khoisan men and alien women. Overall, about a third of today's “Cape Coloured” genes are Khoisan, a third are from black Africa, and the rest from Europeans. By contrast, 60% of their mitochondria—passed through females—are of Khoisan origin, and just one in 20 “Cape Coloured” Y chromosomes descends from a Khoisan man. Any member of that group who decided to trace their ancestry would find their distant grandfathers and grandmothers living in very different places, and at different times. DNA from fossil bones now hints that such a forced hybridisation might have taken place between the ancient emigrants from Africa and the resident European and Asian Neanderthals. Those relationships have left an imprint on British genes, with up to 3% of the sequence in some people of Neanderthal origin. Altogether, more than half the entire Neanderthal genome might be preserved, scattered through the world's modern non-African populations. Surprisingly, Europeans might have got their light skins from their red-haired and extinct cousins, for one of the pigment-reducing genes of Europeans seems to be of Neanderthal origin. East Asians, who have Neanderthal genes of their own, do not seem to have picked up that one, and lightened their skins in a different way on their journey. That ancient episode gets to the heart of a major issue in evolution. What, after all, is a species? The topic is discussed with theological intensity by biologists. One definition that works reasonably for mammals is the “biological species concept”; that if two populations can exchange genes then they belong to the same species. The poodle lost its identity a few years ago, when the domestic dog's official name was changed from Canis familiaris to Canis lupus—a title shared by the wolf. The logic is that wolves and dogs often hybridise where they overlap, with most wolves now containing domestic genes. They must hence, by that definition, belong to the same species. Dogs emerged some 35 000 years ago, which is only about twice the number of generations as that since the split of humans and Neanderthals. Should we reinvent, or abolish, the Neanderthals as a result? And what about all those other confidently titled ancestral species shown in the exhibition? Are we explaining the past just by naming it? The exhibition has videos of the great and good claiming to have more, or fewer, Neanderthal genes than average. Alice Roberts tells us proudly that she is 2·7% Neanderthal—she blames her mother—while my University College London colleague Maggie Aderin-Pocock is slightly disappointed that her African origin means she has none. Clive Anderson speaks in Biblical terms of the escape from a Garden of Eden and suggests that his Scandinavian Y chromosome explains why he likes the cold. The allure of noble descent is always around the corner (Bill Bailey fantasises, with some irony, about his Danish royal blood), and many people now pay good money to the DNA industry to chase it down. In truth, the business is much murkier than it seems. Y chromosomes and mitochondria do track down maternal and paternal asexual lines but—as the “Cape Coloureds” show—Adam and Eve usually come from quite different places (and Eve probably died long before her partner was born). We are linked to the past not just through the pure male, or the pure female, lines but through the billions of people who have indulged in sexual reproduction. Sex unites the human race. A hunt for shared ancestry through males and females can zigzag through history, from son to mother to grandfather, or from daughter to father to grandmother. It finds a common root far sooner than does the tedious plod to Adam or to Eve. Around half the visitors to this exhibition are, without realising it, rubbing shoulders with a sixth cousin, who shared an ancestor with them at about the time the Natural History Museum was built. Almost all native Britons trace descent from a single anonymous individual who lived around the time of Edward I, in the 13th century. On the global scale, universal common ancestry emerges no more than a hundred generations ago—well into Old Testament times, at around 600 BC. Project the figures into the future, and someone alive today—we know not whom—will be the universal ancestor of the world population 3000 years from now. It will, I am sure, not be me, as I have no children. The exhibition has the usual Exit Through the Gift Shop, well supplied with skull-based crockery, together with piles of books on human evolution and genetics. The usual suspects are (almost) all there: Alice Roberts, Chris Stringer, Richard Dawkins, and all; but no Jones, as my vapourings on such topics are nowhere to be seen. Fair enough, I suppose, for if geography is about maps and history about chaps, palaeontology is about gaps, and I, like most ancient Britons, including almost all my literary, skeletal, and genetic predecessors, seem to have fallen into one. Steve Jones' latest book, The Serpent's Promise (Abacus, £9·99), is just out in paperback. It says quite a lot about ancestry.