Jared Diamond - The rise and fall of the third chimpanzee

The identity of that ingredient poses an archaeological puz/le without an accepted answer. To help focus our speculations, let me recapitulate the pieces of the puzzle.

Some groups of humans who lived in Africa and the Near East over 60,000 years ago were quite modern in their anatomy, as far as can be judged from their skeletons, but they were not modern in their behaviour. They continued to make Neanderthal-like tools and to lack innovation..The ingredient that produced the Great Leap Forward does not show up in fossil skeletons. There is another way to restate that puzzle. We share ninety-eight per cent of our genes with chimpanzees (Chapter One). The Africans making Neanderthal-like tools just before our sudden rise to humanity had covered almost all of the remaining genetic distance between us and chimps, to judge from their skeletons. Perhaps they shared 99.9 % of their genes with us. Their brains were as large as ours, and Neanderthals' brains were even slightly larger. The missing ingredient may have been a change in only 0.1 % of our genes. What tiny change in genes could have had such enormous consequences?

Like some other scientists who have speculated about this question, I can think of only one plausible answer: the anatomical basis for spoken complex language. Chimpanzees, gorillas, and even monkeys are capable of symbolic communication not dependent on spoken words. Both chimpanzees and gorillas have been taught to communicate by means of sign language, and chimpanzees have learned to communicate via the keys of a large computer-controlled console. Individual apes have thus mastered 'vocabularies' of hundreds of symbols. While scientists argue over the extent to which such communication resembles human language, there is little doubt that it constitutes a form of symbolic communication. That is, a particular sign or computer key symbolizes a particular something else.

Primates can use not only signs and computer keys, but also sounds, as symbols. For instance, wild vervet monkeys have a natural form of symbolic communication based on grunts, with slightly different grunts to mean leopard', 'eagle', and 'snake'. A month-old chimpanzee named Viki, adopted by a psychologist and his wife and reared virtually as their daughter, learned to 'say' approximations of four words: 'papa', 'mama', 'cup', and 'up'. (The chimp breathed rather than spoke those words.) Given this capability for symbolic communication using sounds, why have apes not gone on to develop much more complex natural languages of their own? The answer seems to involve the structure of the larynx, tongue, and associated muscles that give us fine control over spoken sounds. Like a Swiss watch, all of whose many parts have to be well-designed for the watch to keep time at all, our vocal tract depends on the precise functioning of many structures and muscles. Chimps are thought to be physically incapable of producing several of the commonest human vowels. If we too were limited to just a few vowels and consonants, our own vocabulary would be greatly reduced. For example, take this paragraph, convert all vowels other than 'a' or 'i' to either of those two, convert all consonants other than 'd' or 'm' or V to one of those three, and then see how much of the paragraph you can still understand. Therefore, the missing ingredient may have been some modifications of the proto-human vocal tract to give us finer control and permit formation of a much greater variety of sounds. Such fine modifications of muscles need not be detectable in fossil skulls.

It is easy to appreciate how a tiny change in anatomy resulting in capacity for speech would produce a huge change in behaviour. With language, it takes only a few seconds to communicate the message, 'Turn sharp right at the fourth tree and drive the male antelope towards the reddish boulder, where I'll hide to spear it. Without language, that message could be communicated only with difficulty, if at all. Without language, two proto-humans could not brainstorm together about how to devise a better tool, or about what a cave painting might mean. Without language, even one proto-human would have had difficulty thinking out for himself or herself how to devise a better tool.

I do not suggest that the Great Leap Forward began as soon as the mutations for altered tongue and larynx anatomy arose. Given the right anatomy, it must have taken humans thousands of years to perfect the structure of language as we know it—to arrive at the concepts of word order and case endings and tenses, and to develop vocabulary. In Chapter Eight I shall consider some possible stages by which our language might have become perfected. But if the missing ingredient did consist of changes in our vocal tract that permitted fine control of sounds, then the capacity for innovation would follow eventually. It was the spoken word that made us free. This interpretation seems to me to account for the lack of evidence for Neanderthal/Cro-Magnon hybrids. Speech is of overwhelming importance in the relations between men and women and their children. That is not to deny that mute or deaf people learn to function well in our culture, but they do so by learning to find alternatives for a spoken language that already exists. If Neanderthal language was much simpler than ours or non-existent, it is not surprising that Cro-Magnons did not choose to marry Neanderthals.

I have argued that we were fully modern in anatomy and behaviour and language by 40,000 years ago, and that a Cro-Magnon could have been taught to fly a jet aeroplane. If so, why did it take so long after the Great Leap Forward for us to invent writing and build the Parthenon? The answer may be similar to the explanation why the Romans, great engineers that they were, didn't build atomic bombs. To reach the point of building an A-bomb required two thousand years of technological advances beyond Roman levels, such as the invention of gunpowder and calculus, the development of atomic theory, and the isolation of uranium. Similarly, writing and the Parthenon depended on tens of thousands of years of cumulative developments after the arrival of Cro-Magnons—developments that included the bow and arrow, pottery, domestication of plants and animals, and many others.

Until the Great Leap Forward, human culture had developed at a snail's pace for millions of years. That pace was dictated by the slow rate of genetic change. After the Leap, cultural development no longer depended on genetic change. Despite negligible changes in our anatomy, there has been far more cultural evolution in the past 40,000 years than in the millions of years before. Had a visitor from outer space come to the Earth in Neanderthal times, humans would not have stood out as unique among the world's species. At most, the visitor might have mentioned humans along with beavers, bowerbirds, and army ants as examples of species with curious behaviour. Would the visitor have foreseen the change that would soon make us the first species, in the history of life on Earth, capable of destroying all life?

Chapter two traced our evolutionary history through the appearance of humans with fully modern anatomy and behavioural capabilities, but that chapter does not prepare us to go straight on to consider in more detail the development of human cultural hallmarks, such as language and art. That is because Chapter Two took up only the evidence of bones and tools. Yes, our evolution of large brains and upright posture was prerequisite to language and art, but that was not enough by itself. Human bones alone do not guarantee humanity. Instead, our rise to humanity also required drastic changes in our life-cycle, which will be the subject of Part Two of this book. For any species one can describe what biologists term its 'life-cycle'. That means traits such as the number of offspring produced per litter or birth; the interval between births; the parental care (if any) that offspring receive from the mother or father; social relations between adult individuals; how a male and female select each other to mate with; frequency of sexual relations; and longevity. We take the forms of these traits as they exist in humans for granted, as the norm, but our life-cycle is actually bizarre by animal standards. All the traits that I have just mentioned vary greatly between species, and we are extreme in most respects. To mention only some obvious examples, most animals produce litters much larger than one baby at a time, most animal fathers provide no parental care, and few other animal species live even a small fraction of three-score years and ten.