Ideas: A History from Fire to Freud

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