There are two candidates for humankind’s first idea, one rather more hypothetical than the other. The more hypothetical relates to bipedalism. For a long time, ever since the publication of The Descent of Man by Charles Darwin in 1871, the matter of bipedalism was felt to be a non-issue. Following Darwin, everyone assumed that man’s early ancestors descended from the trees and began to walk upright because of changes in the climate, which made rainforest scarcer and open savannah more common. (Between 6.5 million and 5 million years ago, the Antarctic ice-cap sucked so much water from the oceans that the Mediterranean was drained dry.) This dating agrees well with the genetic evidence. It is now known that the basic mutation rate in DNA is 0.71 per cent per million years. Working back from the present difference between chimpanzee and human DNA, we arrive at a figure of 6.6 million years ago for the chimpanzee–human divergence.5
Several species of bipedal ape have now been discovered in Africa, all the way back to Sahelanthropus, who lived six to seven million years ago in the Djurab desert of Chad and was close to the common ancestor for chimpanzees and humans.6 But the human ancestor which illustrates bipedalism best is Australopithecus afarensis, better known as ‘Lucy’, because on the night she was discovered the Beatles’ song ‘Lucy in the Sky with Diamonds’ was playing in the palaeontologists’ camp. Enough of Lucy’s skeleton survives to put beyond doubt the fact that, by 3.4 to 2.9 million years ago, early humans were bipedal.
It is now believed that the first and most important spurt in the brain size of man’s direct ancestors was associated with the evolution of bipedalism. (Most important because it was the largest; there is evidence that our brains are, relative to our bodies, slightly smaller now than in the past.)7 In the new, open, savannah-type environment, so it is argued, walking upright freed the arms and hands to transport food to the more widely scattered trees where other group members were living. It was bipedalism which also freed the hands to make stone tools, which helped early man change his diet to a carnivorous one which, in providing much more calorie-rich food, enabled further brain growth. But there was a second important consequence: the upright posture also made possible the descent of the larynx, which lies much lower in the throat of humans than in the apes.8 At its new level, the larynx was in a much better position to form vowels and consonants. In addition, bipedalism also changed the pattern of breathing, which improved the quality of sound. Finally, meat, as well as being more nutritious, was easier to chew than tough plant material, and this helped modify the structure of the jaw, encouraging fine muscles to develop which, among other things, enabled subtler movements of the tongue, necessary for the varied range of sounds used in speech. Cutting-tools also supplemented teeth which may therefore have become smaller, helpful in the development of speech. None of this was ‘intended’, of course; it was a ‘spin-off’ as a result of bipedalism and meat-eating. A final consequence of bipedalism was that females could only give birth to relatively small-brained offspring – because mothers needed relatively narrow pelvises to be able to walk efficiently. From this it followed that the infants would be dependent on their mothers for a considerable period, which in turn stimulated the division of labour between males and females, males being required to bring back food for their mates and offspring. Over time this arrangement would have facilitated the development of the nuclear family, making the social structure of the cognitive group more complex. This complex structure, in which people were required to predict the behaviour of others in social situations, is generally regarded as the mechanism by which consciousness evolved. In predicting the behaviour of others, an individual would have acquired a sense of self.
This is all very neat. Too neat, as it turns out. Whereas early humans began walking upright six million years ago, the oldest stone tools are about 2.5 to 2.7 million years old (and maybe even three million years old) – too long a time-lag for the developments to be directly linked. Second, modern experiments have shown that bipedalism does not increase energy efficiency, and as more fossils have been found we now recognise that early bipedal apes lived in environments where trees were plentiful.9 In these circumstances, Nina Jablonski and George Chaplin, of the California Academy of Sciences, have suggested that the real reason humans became bipedal was as a way to appear bigger and more threatening in contests with other animals, and in so doing avoid punishing conflicts and gain access to food. The idea behind this is taken from observations of gorilla and chimpanzee behaviour in the wild. Both types of ape stand upright, swagger, wave their arms about and beat their chests when threatening others in contests over food or sexual partners. Such displays are not always effective but they are often enough for Jablonski and Chaplin to suggest that ‘individuals who learned to defuse tense situations with bipedal displays could have reduced their risk of injury or death and thus, by definition, improved their reproductive chances’. On this scenario, then, bipedalism, though a physical change to the body frame of early humans, developed because it had behavioural – psychological – consequences of an evolutionary kind. Almost certainly, however, it too had a large instinctive element, and for that reason can at best be called a proto-idea.10
The second candidate for man’s earliest idea is much better documented. This is the emergence of stone tools. As we shall see, the manufacture of stone tools went through at least five major phases in pre-history, as early man’s handling of raw stone became more sophisticated. The most important dates to remember, when major changes in technology occurred, are 2.5 million years ago, 1.7 million, 1.4 million, 700,000, and 50,000–40,000 years ago.11 The oldest artefacts yet discovered come from the area of the river Gona in Ethiopia. They consist mainly of selected volcanic pebbles from ancient streambeds and are often difficult to distinguish from naturally occurring rocks. At some point, about 2.5 million years ago, ancient man learned that if he struck one stone against another in a particular way, a thin, keen-edged flake could be knocked off which was sharp enough to pierce the hide of a dead zebra, say, or a gazelle. To the untutored eye, a primitive stone axe from Gona looks little different from any pebble in the area. Archaeologists have noticed, however, that when a flake is deliberately manufactured by another rock being struck against it, it usually produces a distinctive swelling, known as a ‘bulb of percussion’ immediately next to the point of impact. This is used by professionals to distinguish human artefacts from mere broken stones arising from natural ‘collisions’ as a result, for example, of water action.12
Although a cultural artefact, the link between stone tools and man’s later biological development was momentous. This is because, until 2.5 million years ago, early man’s diet was vegetarian. The invention of stone tools, however, enabled him to eat meat – to get at the muscles and internal organs of big and small game – and this had major consequences for the development of the brain. All mammals – primates, and especially humans – are highly encephalised: they have brains that are large when compared with their body mass. Compared with reptiles of the same size, for example, mammals have brains that are, roughly, four times as big.13 In modern humans, the brain comprises only 2 per cent of body weight, but it consumes 20 per cent of the body’s metabolic resources. As we shall see, each major change in stone technology appears to have been accompanied by an increase in brain size, though later increases were nowhere near as large as the first spurt.14