The era known as the Cenozoic begins with the mass extinctions 65 million years ago and has continued right up to the present. During this era, the continents continued to drift, separate and collide. This created new environmental conditions. In the first 20 million years, temperatures continued to rise, and a tropical zone appeared, in which conditions in Britain, for example, resembled those of a Malaysian jungle. The most important development in evolution in this era was the extraordinarily rapid rise of the mammals, which took over the environments vacated by the reptiles. By 40 million years ago, primates, elephants, pigs, rodents, horses, sea cows, porpoises, whales and bats, as well as most orders of modern birds and many families of plants, had all appeared.

The rise of the mammals might be seen as a kind of triumphal procession, in which evolution progresses ever upwards, in an unbroken line, culminating finally in the birth of humankind, the crowning glory of creation. But this was far from the case. Evolution was never a straight line, as we have seen. Periods of intense growth were, in this period also, followed by dramatic reversals, death and extinction. The two main periods of extinction are linked with sharp environmental changes. By 40-30 million years ago, we observe the beginnings of a cooling process. Temperature fell continuously for the next 25 million years, only stabilising at its present level five million years ago. That period witnessed the first recent period of extinctions affecting mammals.

The primates, the ancestors of apes and of humans, were spread all over the world. The period of extinction of the dinosaurs had an effect on many of these families. The new environmental conditions led to the development of a new species – the proto-apes, better adapted to the changed conditions. It is worth mentioning that the new conditions mainly influenced Africa and Euro-Asia, and not America. By this time, Antarctica reached the South Pole and began to be covered in ice. For the next 10-20 million years, there was a further period of explosive growth of mammals – the biggest ever – in which many species of apes appeared. However, the basic design of the apes remained unchanged throughout this period, until a new sharp climatic shift brought about a transformation. There are considerable disagreements among palaeontologists on the question of when and how the hominids separated from the apes. There are indications from bones that as far back as 14 million years ago there was already a species that resembled modern apes. Scientists believe that these bones belong to a species which lived both in Africa and Euro-Asia from 14-7 million years ago. It appears to have been a very successful species, and represents the common ancestor of humans, apes and gorillas. Then, 10-7 million years ago, there was a new and dramatic environmental change.

Glaciers already covered Antarctica. Now the ice-sheet spread, not only in the South, but in the North, where it covered Alaska, North America, and North Europe. Since more and more water was trapped in the ice, the sea level began to decline. It has been estimated that the fall in sea levels was more than 150 metres at that time. As a result, new landmasses appeared, joining the continents; land bridges were formed connecting Europe and Africa, Asia and America, Britain and Europe, thus making possible further migrations of species. The Mediterranean Sea completely evaporated. The climate around the equator became very dry, causing extensive desertisation, together with a massive decline of jungles and forests, and the emergence of vast expanses of savannahs and open land. By this time, Asia was separated from Africa by deserts, thus cutting off the African apes from their Asian cousins. Inevitably, this was another period of extinction and death. But it was equally a period of the birth of new species. At a certain point, possibly seven million years ago, the development of mammals resulted in the emergence of the first hominids (human-like primates).

It is now generally accepted that humankind originated in Africa. By 5.3 million years ago, the Mediterranean assumed its present form, and a new species of ape developed in Africa, which, in the course of a million years, developed in three different directions, giving rise eventually to apes, hominids and gorillas. The separation of these three branches occurred about 4-5 million years ago as a result of environmental pressure in Eastern Africa. The spread of the glaciers to South Africa resulted in a dramatic change in Eastern Africa – severe depletion of forests, because of reduced rainfall and a generally drier climate. This was probably the driving-force which led to the separation of the three species of proto-apes. Hitherto, they had lived in trees. Now they had three options:

1) Part of them remained in the forests. These must have been the most skilful, strongest and most successful in extracting food from limited sources. However, the decline of the forest habitat must have severely depleted their numbers. The remnant of this branch is represented by the modern gorillas.

2) Another group, forced to move to the margins of the forests, with fewer trees and less food resources, eventually were forced to increase their food-gathering range by moving on the ground, while remaining near the trees for protection. This group is represented by the modern chimpanzees.

3) A third group, probably made up of the weaker and less skilful section of the species, were compelled by intense competition for scarce food resources to move out of the forest altogether. They were thus forced not only to move on the ground, but to cover long distances in order to find the food necessary for their survival. They were compelled to develop an entirely new way of living, radically different to that of other primates.

Environmental pressures in Asia caused by climatic changes also drove some groups of monkeys to the fringes of the forests. These developed into the modern baboons, which move on the ground in search of food, but return to the trees for protection. Primates exhibit a variety of modes of locomotion. The tarsier leaps and clings; the gibbon swings from limb to limb; the orangutan is “four-handed”; the gorilla is a knuckle walker; the monkey is a true quadruped; only hominids have ventured to become completely bipedal.

“Other specialisations have gone with handedness. If one is going to jump and snatch, one had better be able to judge distances accurately. If not, one will come up empty-handed at best; at worst, one will miss the branch entirely and fall. The way to precise distance judgment is via binocular vision: focusing two eyes on an object to provide depth perception. That requires that the eyes be set in the front of the skull and facing forward, not on the sides of the head, as a squirrel’s eyes are. Primate ancestors developed such vision. Their skulls become rounded to accommodate the new position of the eyes, and with that change in shape came an enlargement of the skull capacity and the opportunity to have a larger brain. At the same time, the jaw became smaller. With hands, an animal does not have to do all its foraging and hunting with its teeth. It can afford a shorter jaw and fewer teeth. Modern apes and monkeys – and humans – have sixteen teeth in each jaw. Their ancestors had as many as twenty two.” (Johansen and Edey)[30]

The pioneering American psychologist Jerome Bruner, in his writings on the mental development of children, has stressed that skilled behaviour has much in common with language production on the one hand and problem-solving on the other. The simplest skills almost all involve the use of the hand or hands and the visual guidance. On the development of the human hand, Bruner writes the following:

The hands of man are a slow-growing system, and it is many years before humans can exhibit the kind of manual intelligence that has distinguished our species from others – the using and making of tools. Indeed, historically, the hands were regarded even by students of primate evolution as of no particular interest. Wood Jones would have us to believe that there was little morphological difference between the monkey hand and that of man, but that the difference was in the function to which they were put by the central nervous system. Yet, as Clark and Napier have pointed out, it is the evolutionary direction of morphological change in the hand, from tree shrews through New World monkeys through Old World monkeys to man, that should reveal how the function of the hand has changed and, with it, the nature of the implementation of human intelligence.

That change has been steadily in the direction of a very special form of despecialisation. The hand is free from its locomotor function, from its brachiating function, and from such specialised requirements as were answered by claws and by exotic forms of finger pads. Becoming more despecialised in function means becoming more varied in the functions that can be fulfilled. Without losing its capacity for phalangeal divergence needed for weight-wearing, convergence for cupping food, prehensility for holding and climbing, or opposability – all part of an early primate heritage – the hand in the later primate evolution achieves several new functional capacities while undergoing appropriate morphological change as well. A combined capacity for power and precision grip is added.

The flexibility of the palm and thumb increases through changes in the hamate and trapezium bones in their articulation. The thumb lengthens and its resting angle to the hand increases. The terminal phalanges broaden and strengthen, particularly the thumb. Napier may exaggerate when he says, ‘The present evidence suggests that the stone implements of early man were as good (or as bad) as the hand that made them.’ For surely, initially stupid hands become clever when employed in a clever programme devised by the culture.[31]

The first hominid fossils were found in East Africa, and belong to the species known as Australopithecus afarensis, which lived around 3.9-3.0 million years ago. These ape-like creatures were able to walk upright, possessed hands with thumbs fully opposed to the fingers, and therefore capable of manipulating tools. Their cranial capacity was larger than other apes (450 ccs.). As yet, no tools have been found in connection with these early hominids, but are clearly in evidence when we come to the first clearly identifiable human species, the aptly-named Homo habilis (“handyman”), which walked upright, had a height of 1.20 metres and had a brain capacity of 800 cubic centimetres.

At what point does the real separation of humans from hominid apes take place? Palaeontologists have argued for a long time over this question. The answer was given by Engels in his masterly essay The Part Played by Labour in the Transition of Ape to Man. But it was already anticipated by Marx and Engels much earlier in their pioneering work, The German Ideology, written in 1845:

Men can be distinguished from animals by consciousness, by religion or anything else you like. They themselves begin to distinguish themselves from animals as soon as they begin to produce their means of subsistence, a step which is conditioned by their physical organisation. By producing their means of subsistence men are indirectly producing their material life.[32]

  1. Johanson, D. and Edey, M. op. cit., p. 320.

  2. Bruner, J. Beyond the information Given, pp. 246-7.

  3. MECW, Vol. 5, p. 31.