Despite our instant sympathy with Cro-Magnon art, their stone tools and hunter-gatherer lifestyle make it hard for us to view them as other than primitive. Stone tools evoke cartoons of club-waving cavemen uttering grunts as they drag a woman off to their cave. We can form a more accurate impression of Cro-Magnons if we imagine what future archaeologists will conclude after excavating a New Guinea village site from as recently as the 1950s. The archaeologists will find a few simple types of stone axes. Virtually all other material possessions were made of wood and will have perished. Nothing will remain of the multistorey houses, beautifully woven baskets, drums and flutes, outrigger canoes, and world-quality painted sculpture. There will be no trace of the village's complex language, songs, social relationships, and knowledge of the natural world.

New Guinea material culture was until recently 'primitive' (that is, stone-age) for historical reasons, but New Guineans are fully modern humans. New Guineans whose fathers lived in the Stone Age now pilot aeroplanes, operate computers, and govern a modern state. If we could carry ourselves back 40,000 years in a time machine, I expect that we Would find Cro-Magnons to be equally modern people, capable of learning to fly a jet plane. They made stone and bone tools only because no other tools had yet been invented; that is all that they had the opportunity to learn.

It used to be argued that Neanderthals evolved into Cro-Magnons within Europe. That possibility now seems increasingly unlikely. The last Neanderthal skeletons from around 40,000 years ago were still 'fullblown' Neanderthals, while the first Cro-Magnons appearing in Europe at the same time were already anatomically fully modern. Since anatomically modern people were already present in Africa and the Near East tens of thousands of years earlier, it seems much more likely that anatomically modern people invaded Europe from that direction than that they evolved within Europe.

What happened when invading Cro-Magnons met the resident Neanderthals? We can be certain only of the end result: within a short time, no more Neanderthals. The conclusion seems to me inescapable that Cro-Magnon arrival somehow caused Neanderthal extinction. Yet many archaeologists recoil at this conclusion and invoke environmental changes instead. For example, the Encyclopaedia Britannica's fifteenth edition concludes its entry for Neanderthals with the sentence, 'The disappearance of the Neanderthals, although it cannot yet be fixed in time, was probably the result of being creatures of an interglacial period unable to avoid the ravages of another Ice Age. In fact, Neanderthals thrived during the last Ice Age, and suddenly disappeared over 30,000 years after its start and an equal time before its end.

My guess is that events in Europe at the time of the Great Leap Forward were similar to events that have occurred repeatedly in the modern world, whenever a numerous people with more advanced technology invades the lands of a much less numerous people with less advanced technology. For instance, when European colonists invaded North America, most North American Indians proceeded to die of introduced epidemics; most of the survivors were killed outright or driven off their land (Chapter Sixteen); some of the survivors adopted European technology (horses and guns) and resisted for some time; and many of the remaining survivors were pushed on to lands that Europeans did not want, or else intermarried with Europeans (Chapter Fifteen). The displacement of Aboriginal Australians by European colonists, and of southern African San populations (Bushmen) by invading iron-age Bantu-speakers, followed a similar course. By analogy, I guess that Cro-Magnon diseases, murders, and dis-44-JUST ANOTHER SPECIES OF BIG MAMMAL placements did in the Neanderthals. If so, then the Cro-Magnon/ Neanderthal transition was a harbinger of what was to come, when the victors' descendants began squabbling among themselves. It may at first seem paradoxical that Cro-Magnons prevailed over the far more muscular Neanderthals, but weaponry rather than strength would have been decisive. Similarly, it's not gorillas that are now threatening to exterminate humans in Central Africa, but vice versa. People with huge muscles require lots of food, and they therefore gain no advantage if slimmer, smarter people can use tools to do the same work.

Like the Great Plains Indians of North America, some Neanderthals may have learned some Cro-Magnon ways and resisted for a while. This is the only sense I can make of a puzzling culture called the Chatel-perronian, which coexisted in Western Europe along with a typical Cro-Magnon culture (the so-called Aurignacian culture) for a short time after Cro-Magnons arrived. Chatelperronian stone tools are a mixture of typical Neanderthal and Cro-Magnon tools, but the bone tools and art typical of Cro-Magnons are usually lacking. The identity of the people who produced Chatelperronian culture was debated by archaeologists, until a skeleton unearthed with Chatelperronian artifacts at Saint-Cesaire in France proved to be Neanderthal. Perhaps, then, some Neanderthals managed to master some Cro-Magnon tools and hold out longer than their fellows. What remains unclear is the outcome of the interbreeding experiment posed in science-fiction novels. Did some invading Cro-Magnon men mate with some Neanderthal women? No skeletons that could reasonably be considered Neanderthal/Cro-Magnon hybrids are known. If Neanderthal behaviour was as relatively rudimentary, and Neanderthal anatomy as distinctive, as I suspect, few Cro-Magnons may have wanted to mate with Neanderthals. Similarly, although humans and chimps continue to coexist today, I am not aware of any matings. While Cro-Magnons and Neanderthals were not nearly as different, the differences may still have been a mutual turn-off. And if Neanderthal women were geared for a twelve-month pregnancy, a hybrid foetus might not have survived. My inclination is to take the negative evidence at face value, to accept that hybridization occurred rarely if ever, and to doubt that living people of European descent carry any Neanderthal genes.

So much for the Great Leap Forward in Western Europe. The replacement of Neanderthals by modern people occurred somewhat earlier in Eastern Europe, and still earlier in the Near East, where possession of the same area apparently shifted back and forth between Neanderthals and modern people from 90,000 to 60,000 years ago. The slowness of the transition in the Near East, compared to its speed in western Europe, suggests that the anatomically modern people living around the Near East before 60,000 years ago had not yet developed the modern behaviour that ultimately let them drive out the Neanderthals.

Thus, we have a tentative picture of anatomically modern people arising in Africa over 100,000 years ago, but initially making the same tools as Neanderthals and having no advantage over them. By perhaps 60,000 years ago, some magic twist of behaviour had been added to the modern anatomy. That twist (of which more in a moment) produced innovative, fully modern people who proceeded to spread westward into Europe, quickly supplanting Europe's Neanderthals. Presumably, those modern people also spread east into Asia and Indonesia, supplanting the earlier people there of whom we know little. Some anthropologists think that skull remains of those earlier Asians and Indonesians show traits recognizable in modern Asians and Aboriginal Australians. If so, the invading moderns may not have exterminated the original Asians without issue, as they did the Neanderthals, but instead interbred with them.

Two million years ago, several proto-human lineages had coexisted side by side until a shake-up left only one. It now appears that a similar shake-up occurred within the last 60,000 years, and that all of us alive in the world today are descended from the winner of that upheaval. What was the last missing ingredient whose acquisition helped our ancestor to win?