THE GREAT LEAP FORWARD
What happened at that magic moment in evolution around 40,000 years ago, when we suddenly became human?
As we saw in Chapter One, our lineage diverged from that of apes millions of years ago. For most of the time since then, we have remained little more than glorified chimpanzees in the ways we have made our living. As recently as/40,000 years ago, Western Europe was still occupied by Neanderthals, primitive beings for whom art and progress scarcely existed. Then there was an abrupt change, as anatomically modern people appeared in Europe, bringing with them art, musical instruments, lamps, trade, and progress. Within a short time, the Neanderthals were gone. That Great Leap Forward in Europe was probably the result of a similar leap that had occurred over the course of the preceding few tens of thousands of years in the Near East and Africa. Even a few dozen millenia, though, is a trivial fraction (less than one per cent) of our millions of years of history separate from that of the apes. Insofar as there was any single point in time when we could be said to have become human, it was at the time of that leap. Only a few more dozen millenia were needed for us to domesticate animals, develop agriculture and metallurgy, and invent writing. It was then but a short further step to those monuments of civilization that distinguish humans from animals acros's what used to seem an unbridgeable gulf- monuments such as the 'Mona Lisa' and the Eroica Symphony, the Eiffel Tower and Sputnik, Dachau's ovens and the bombing of Dresden.
This chapter will confront the questions posed by our abrupt rise to humanity. What made it possible, and why was it so sudden? What held back the Neanderthals, and what was their fate? Did Neanderthals and modern peoples ever meet, and if so, how did they behave towards each other?
Understanding the Great Leap Forward is not easy, and writing about it is not easy either. The immediate evidence conies from technical details of preserved bones and stone tools. Archaeologists' reports are full of terms obscure to the rest of us, such as 'transverse occipital torus', 'receding zygomatic arches', and 'Chatelperronian backed knives'. What we really want to understand—the way of life and the humanity of our various ancestors—is not directly preserved but only inferred from those technical details of bones and tools. Much of the evidence is missing, and archaeologists often disagree over the meaning of such evidence as has survived. Since the books and articles listed on pages 334-5 will slake the interest of readers curious to learn more about receding zygomatic arches, I shall emphasize instead the inferences from bones and tools.
Our ancestors were confined to Africa for millions of years, where, as we have already discussed, they diverged from the ancestors of chimps and gorillas between about six and ten million years ago. For comparison, life originated on Earth several billion years ago, and the dinosaurs became extinct around sixty-five million years ago. (Science-fiction films that depict cavemen fleeing from dinosaurs are just that, science fiction.) Initially, our ancestors would have been classified as merely another species of ape, but a sequence of three changes launched us in the direction of modern humans.
The first of these changes had occurred by around four million years ago, when the structure of fossilized limb bones shows that our ancestors were habitually walking upright on the two hindlimbs. In contrast, gorillas and chimps walk upright only occasionally, and usually proceed on all fours. The upright posture freed our ancestors' forelimbs to do other things, among which tool-making proved the most important.
The second change occurred around three million years ago, when our lineage split into at least two distinct species. Recall that members of two animal species living in the same area must fill different ecological roles and do not normally interbreed with each other. For example, coyotes and wolves are obviously closely related and (until wolves were exterminated in most of the US) lived in many of the same areas of North America. However, wolves are larger, mainly hunt big mammals like deer and moose, and often live in large packs, whereas coyotes are smaller, mainly hunt small mammals like rabbits and mice, and usually live in pairs or small groups. Similarly, Europe's wildcat and lynx are closely related and overlap widely in range but differ ecologically and do not interbreed.
Every human population living today has interbred with every other human population with which it has had extensive contact. Ecological differences among existing humans are entirely a product of childhood education: it is not the case that some of us are born with sharp teeth and equipped to hunt deer, while others are born with grinding teeth, gather berries, and do not marry the deerhunters. Therefore all modern humans belong to the same species.
On perhaps two occasions in the past, however, the human lineage split into separate species, as distinct as wolves and coyotes. The most recent such occasion, which I shall describe later, may have been at the time of the Great Leap Forward. The earlier occasion was around three million years ago, when our lineage split into two: a man-ape with a robust skull and very big cheek teeth, assumed to eat coarse plant food, and often referred to as Australopithecus robustus (meaning 'the robust southern ape'); and a man-ape with a more lightly built skull and smaller teeth, assumed to have an omnivorous diet, and known as Australopithecus africanus ('the southern ape of Africa') >The latter man-ape evolved into a larger-brained form termed Homo habilis ('man the handyman'). However, fossil bones often attributed to male and female Homo habilis differ so much in skull size and tooth size that they may actually imply another fork in our lineage yielding two distinct kahilis-like species: Homo habilis himself, and a mysterious 'Third Man'. Thus, two million years ago there were at least two, and possibly three, proto-human species. The third and last of the big changes that began to make our ancestors more human and less apelike was the regular use of stone tools. This is a human hallmark with clear animal precedents: woodpecker finches, Egyptian vultures, and sea otters are among the other animal species that evolved independently to employ tools in capturing or processing food, though none of these species is as heavily dependent on implements as we are now. Common chimpanzees also use tools, occasionally of stone, but not in numbers sufficient to litter the landscape. But by around two-and-a-half million years ago, very crude stone tools appear in numbers in areas of East Africa occupied by the proto-humans. Since there were two or three proto-human species, who made the tools? Probably the light-skulled species, since both it and the tools persisted and evolved. With only one human species surviving today but two or three a few million years ago, it is clear that one or two species must have become extinct. Who was our ancestor; which species ended up instead as a discard in the rubbish-heap of evolution; and when did this shakedown occur? The winner was the light-skulled* Homo habilis, who went on to increase in brain size and body size. By around 1,700,000 years ago the differences were sufficient that anthropologists give our lineage a new name, Homo erectus, meaning 'the man that walks upright'. (Homo erectus fossils were discovered before all the earlier fossils I have been discussing, so anthropologists did not realize that Homo erectus was not the first proto-human to walk upright.) The robust man-ape disappeared around 1,200,000 years ago, and the 'Third Man' (if he ever existed) must have disappeared by then also. As for why Homo erectus survived and the robust man-ape didn't, we can only speculate. A plausible guess is that the robust man-ape could no longer compete, since Homo erectus ate both meat and plant food, and since tools and a larger brain made Homo erectus more efficient at getting even the plant food on which his robust sibling depended. It is also possible that Homo erectus gave his sibling a direct push into oblivion, by killing him for meat.