The Penguin History of the World

The next clear stage in human evolution is nothing less than a revolution in physique. After a divergence between hominins and more ape-like creatures, which occurred around 5 million years ago, it took rather less than 2 million years for one successful family of hominins to increase its brain size to about twice that of Australopithecus. One of the most important stages of this process, and some of the most crucial in the evolution of humanity, were already reached in a species called Homo erectus. It was already widespread and successful a million years ago, and had by then spread into Europe and Asia. The oldest specimen of the species so far found may be about half a million years older than that, while the last evidence for its survival (from Indonesia) suggests members of it were still living between 10,000 and 15,000 years ago, well after our own kind had spread throughout most of the earth. Homo erectus therefore successfully exploited a much bigger environment than earlier species and did so for much longer than has Homo sapiens, our species of modern man. Many signs once more point to an African origin and thence to a spread through Europe and Asia (where Homo erectus was first found). Apart from fossils, a special tool helps to plot the distribution of the new species by defining areas into which Homo erectus did not spread as well as those into which he did. This is the so-called ‘hand-axe’ of stone, whose main use seems to have been for skinning and cutting up large animals (its use as an axe in the usual, hafted sense seems unlikely, but the name is established). There can be no doubt of the success of Homo erectus as a genetic product.

Sub-species of Homo erectus survived for a very long time, and, although few scholars now believe that any of these, at least in their non-African form, is one of our direct ancestors, there is no precise dividing line between them and us (there never is in human prehistory, a fact it is only too easy to overlook or forget). With the different sub-species of Homo erectus we are already dealing with a creature who has added to the upright stance of his predecessors a brain approaching that of modern man in magnitude. Though we still know only a little of the way in which the brain is organized, there is, allowing for body size, a rough correlation between size and intelligence. It is reasonable, therefore, to attribute great importance to the selection of strains with bigger brains and to reckon this a huge advance in the story of the slow accumulation of human characteristics.

Bigger brains meant bigger skulls and other changes too. An increase in antenatal size requires changes in the female pelvis to permit the birth of offspring with larger heads, and another consequence was a longer period of growth after birth; physiological evolution in the female was not sufficient to provide antenatal accommodation to any point approaching physical maturity. Human children need maternal care long after birth. Prolonged infancy and immaturity in their turn imply prolonged dependency: it is a long time before such infants can gather their own food. It may be with the early Homo erectus that there began that long extension of tolerated immaturity, whose latest manifestation is the maintenance of young people by society during long periods of higher education.

Biological change also meant that care and nurture came gradually to count for more than large litters in ensuring the survival of the species. This in turn implied further and sharper differentiation in the roles of the sexes. Females were being pinned down much more by maternity at a time when food-gathering techniques seem to have become more elaborate and to demand arduous and prolonged co-operative action by males – perhaps because bigger creatures needed more and better food. Psychologically, too, the change may be significant. A new emphasis on the individual is one concomitant of prolonged infancy. Perhaps it was intensified by a social situation in which the importance of learning and memory was becoming more and more profound and skills more complex. About this point the mechanics of what is going forward begin to slip from our grasp (if, indeed, they were ever in it). We are somewhere near the area in which the genetic programming of the hominids is infringed by learning. This is the beginning of the great change from the natural physical endowment to tradition and culture – and eventually to conscious control – as evolutionary selectors, though we may never be able to say where precisely this change occurs.