The Penguin History of the World

One more backward glance is useful before plunging into the still shallow (though gradually deepening) pool of evidence. One hundred million or so years ago, primitive mammals were of two main sorts. Some, rodent-like, remained on the ground; others took or had taken to the trees. In this way the competition for resources was lessened and strains of each survived to people the world with the creatures we know today. In the second group were the prosimians. We are among their descendants, for they were the ancestors of the first primates.

It is best not to be too impressed by talk about ‘ancestors’ in any but the most general sense. Between the prosimians and ourselves lie millions of generations and many evolutionary blind alleys. It is important none the less that our remotest identifiable ancestors lived in trees because what survived in the next phase of evolution were genetic strains best suited to the special uncertainties and accidental challenges of the forest. That environment put a premium on the capacity to learn. Those survived whose genetic inheritance could respond and adapt to the surprising, sudden danger of deep shade, confused visual patterns and treacherous handholds. Strains prone to accident in such conditions were wiped out. Among those that prospered (genetically speaking) were some species with long digits which were to develop into fingers and, eventually, the oppositional thumb, and other forerunners of the apes already embarked upon an evolution towards three-dimensional vision and the diminution of the importance of the sense of smell.

The prosimians were little creatures. Tree-shrews still exist which give us some idea of what they were like; they were far from being monkeys, let alone men. Yet for millions of years they carried the traits which made humanity possible. During this time geography counted for much in their evolution, by imposing limits on contact between different strains, sometimes effectively isolating them, and thus increasing differentiation.

Changes would not happen quickly but it is likely that fragmentations of the environment caused by geographical disturbance led to the isolation of zones in which, little by little, the recognizable ancestors of many modern mammals appeared. Among them are the first monkeys and apes. They do not seem to go back more than 60 million years or so.

These monkeys and apes represent a great evolutionary stride. Both families had much greater manipulative dexterity than any predecessor. Within them, species distinct in size or acrobatic quality began to evolve. Physiological and psychological evolution blur in such matters. Like the development of better and stereoscopic vision, the growth of manipulative power seems to imply a growth of consciousness. Perhaps some of these creatures could distinguish different colours. The brains of the first primates were already much more complex than those of any of their predecessors; they were bigger, too. Somewhere the brain of one or more of these strains became complex enough and its physical powers sufficiently developed for the animal to cross the line at which the world as a mass of undifferentiated sensations becomes at least in part a world of objects. Whenever this happened it was a decisive step towards mastering the world by using it, instead of reacting automatically to it.

Some 25 or 30 million years ago, as desiccation began to reduce the area of the forests, competition for diminishing forest resources became fiercer. Environmental challenge and opportunity appeared where the trees and the grasslands met. Some primates, not powerful enough to hold on to their forest homes, were able, because of some genetic quality, to penetrate the savannahs in search of food and could meet the challenge and exploit the opportunities. Probably they had a posture and movement marginally more like that of men than, say, that of the gorillas or chimpanzees. An upright stance and the capacity to move easily on two feet make it possible to carry burdens, among them food. The dangerous open savannah could then be explored and its resources withdrawn from it to a safer home base. Most animals consume their food where they find it; man does not. Freedom to use the forelimbs for something other than locomotion or fighting also suggests other possibilities. We cannot confirm what the first ‘tool’ was, but primates other than man have been seen to pick up objects which come to hand and wave them as a deterrent, use them as weapons, or investigate and expose possible sources of food with their aid.