Even now, at least thirty thousand years after the fact, the signal is discernible: all non-Africans, from the New Guineans to the French to the Han Chinese, carry somewhere between one and four per cent Neanderthal DNA.
From the archeological record, it’s inferred that Neanderthals evolved in Europe or western Asia and spread out from there, stopping when they reached water or some other significant obstacle. (During the ice ages, sea levels were a lot lower than they are now, so there was no English Channel to cross.) This is one of the most basic ways modern humans differ from Neanderthals and, in Pääbo’s view, also one of the most intriguing. By about forty-five thousand years ago, modern humans had already reached Australia, a journey that, even mid-ice age, meant crossing open water. Archaic humans like Homo erectus “spread like many other mammals in the Old World,” Pääbo told me. “They never came to Madagascar, never to Australia. Neither did Neanderthals. It’s only fully modern humans who start this thing of venturing out on the ocean where you don’t see land. Part of that is technology, of course; you have to have ships to do it. But there is also, I like to think or say, some madness there. You know? How many people must have sailed out and vanished on the Pacific before you found Easter Island? I mean, it’s ridiculous. And why do you do that? Is it for the glory? For immortality? For curiosity? And now we go to Mars. We never stop.” If the defining characteristic of modern humans is this sort of Faustian restlessness, then, by Pääbo’s account, there must be some sort of Faustian gene. Several times, he told me that he thought it should be possible to identify the basis for this “madness” by comparing Neanderthal and human DNA.
Over the decades, many theories have been offered to explain what caused the demise of the Neanderthals, ranging from climate change to simple bad luck. In recent years, though, it’s become increasingly clear that, as Pääbo put it to me, “their bad luck was us.” Again and again, the archeological evidence in Europe indicates, once modern humans showed up in a region where Neanderthals were living, the Neanderthals in that region vanished. Perhaps the Neanderthals were actively pursued, or perhaps they were just outcompeted. The Neanderthals’ “bad luck” is presumably the same misfortune that the hobbits and the Denisovans encountered, and similar to the tragedy suffered by the giant marsupials that once browsed Australia, and the varied megafauna that used to inhabit North America, and the moas that lived in New Zealand. And it is precisely the same bad luck that has brought so many species—including every one of the great apes—to the edge of oblivion today.
“To me, the mystery is not the extinction of the Neanderthals,” Jean-Jacques Hublin, the director of the Institute for Evolutionary Anthropology’s department of human evolution, told me. “To me the mystery is what makes modern humans such a successful group that they have been replacing not just the Neanderthals but everything. We don’t have much evidence that the Neanderthals or other archaic humans ever led to an extinction of a species of mammal or anything else. For modern humans, there are hundreds of examples, and we do it very well.”