The Ascent of Man (3 page)

In a parched African landscape like Omo, man first put his foot to the ground. That seems
a pedestrian way to begin the Ascent of Man, and yet it is crucial. Two million years ago, the first certain ancestor of man walked with a foot which is almost indistinguishable from the foot of modern man. The fact is that when he put his foot on the ground and walked upright, man made a commitment to a new integration of life and therefore of his limbs.

The one to concentrate on, of course,
is the head, because of all human organs it has undergone the most far-reaching and formative changes. Happily, the head leaves a lasting fossil (unlike the soft organs), and though it is less informative about the brain than we should like, at least it gives us some measure of its size. A number of fossil skulls have been found in Southern Africa in the last fifty years which establish the characteristic
structure of the head when it began to be man-like. The picture
here
shows what it looked like over two million years ago. It is a historic skull, found not at Omo, but south of the equator at a place called Taung, by an anatomist called Raymond Dart. It is a baby, five to six years old, and though the face is nearly complete, part of the skull is sadly missing. In 1924 it was a puzzling find,
the first of its kind, and was treated with caution even after Dart’s pioneering work on it.

Yet Dart instantly recognised two extraordinary features. One is that the
foramen magnum
(that is, the hole in the skull that the spinal cord comes up through to the brain) is upright; so that this was a child that held its head up. That is one man-like feature; for in the monkeys and apes the head hangs
forward from the spine, and does not sit upright on top of it. And the other is the teeth. The teeth are always tell-tale. Here they are small, they are square – these are still the child’s milk teeth – they are not the great, fighting canines that the apes have. That
means that this was a creature that was going to forage with its hands and not its mouth. The evidence of the teeth also implies
that it was probably eating meat, raw meat; and so the hand-using creature was almost certainly making tools, pebble-tools, stone choppers, to carve it and to hunt.

Dart called this creature
Australopithecus
. It is not a name that I like; it just means Southern Ape, but it is a confusing name for an African creature that for the first time was not an ape. I suspect that Dart, who was born in
Australia, put a pinch of mischief into his choice of the name.

It took ten years before more skulls were found – adult skulls now – and it was not until late in the 1950s that the story of
Australopithecus
was substantially pieced together. It started in South Africa, then it moved north to Olduvai Gorge in Tanzania, and most recently the richest finds of fossils and tools have turned up in
the basin of Lake Rudolf. This history is one of the scientific delights of the century. It is every bit as exciting as the discoveries in physics before 1940, and those in biology since 1950; and it is as rewarding as either of those in the light that it throws on our nature as human beings.

For me, the little
Australopithecus
baby has a personal history. In 1950, when its humanity was by no means accepted, I was asked to do a piece of mathematics. Could I combine
a measure of the size of the Taung child’s teeth with their shape, so as to discriminate them from the teeth of apes? I had never held a fossil skull in my hands, and I was by no means an expert on teeth. But it worked pretty well; and it transmitted to me a sense of excitement which I remember at this instant. I, at over forty, having spent a lifetime in doing abstract mathematics about the shapes
of things, suddenly saw my knowledge reach back two million years and shine a searchlight into the history of man. That was phenomenal.

And from that moment I was totally committed to thinking about what makes man what he is: in the scientific work that I have done since then, the literature that I have written, and in these programmes. How did the hominids come to be the kind of man that I honour:
dexterous, observant, thoughtful, passionate, able to manipulate in the mind the symbols of language and mathematics both, the visions of art and geometry and poetry and science? How did the ascent of man take him from those animal beginnings to that rising enquiry into the workings of nature, that rage for knowledge, of which these essays are one expression? I do not know how the Taung baby
began life, but to me it still remains the primordial infant from which the whole adventure of man began.

The human baby, the human being, is a mosaic of animal and angel. For example, the reflex that makes the baby kick is already there in the womb – every mother knows that – and it is there in all vertebrates. The reflex is self-sufficient, but it sets the stage for more elaborate movements,
which have to be practised before they become automatic. Here by eleven months it urges the baby to crawl. That brings in new movements, and they then lay down and consolidate the pathways in the brain (specifically the cerebellum, where muscular action and balance are integrated) that will form a whole repertoire of subtle, complex movements and make them second nature to him. Now the cerebellum
is in control. All that the conscious mind
has to do is to issue a command. And by fourteen months the command is ‘Stand!’ The child has entered the human commitment to walk upright.

Every human action goes back in some part to our animal origins; we should be cold and lonely creatures if we were cut off from that blood-stream of life. Nevertheless, it is right to ask for a distinction: What
are the physical gifts that man must share with the animals, and what are the gifts that make him different? Consider any example, the more straightforward the better – say, the simple action of an athlete when running or jumping. When he hears the gun, the starting response of the runner is the same as the flight response of the gazelle. He seems all animal in action. The heartbeat goes up; when
he sprints at top speed the heart is pumping five times as much blood as normal, and ninety per cent of it is for the muscles. He needs twenty gallons of air a minute now to aerate his blood with the oxygen that it must carry to the muscles.

The violent coursing of the blood and intake of air can be made visible, for they show up as heat on infra-red films which are sensitive to such radiation.
(The blue or light zones are hottest; the red or dark zones are cooler.) The flush that we see and that the infra-red camera analyses is a by-product that signals the limit of muscular action. For the main chemical action is to get energy for the muscles by burning sugar there; but three-quarters of that is lost as heat. And there is another limit, on the runner and the gazelle equally, which is
more severe. At this speed, the chemical burn-up in the muscles is too fast to be complete. The waste products of incomplete burning, chiefly lactic acid, now foul up the blood. This is what causes fatigue, and blocks the muscle action until the blood can be cleaned with fresh oxygen.

So far, there is nothing to distinguish the athlete from the gazelle – all that, in one way or another, is the normal metabolism of an animal in flight. But there is a cardinal difference: the runner was not in flight. The shot that set him off was the starter’s pistol, and what
he was experiencing, deliberately, was not fear but exaltation. The runner is like a child at play; his actions are an adventure in freedom, and the only purpose of his breathless chemistry was to explore the limits of his own strength.

Naturally there are physical differences between man and the other animals, even between man and the apes. In the act of vaulting, the athlete grasps his pole,
for example, with an exact grip that no ape can quite match. Yet such differences are secondary by comparison with the overriding difference, which is that the athlete is an adult whose behaviour is not driven by his immediate environment, as animal actions are. In themselves, his actions make no practical sense at all; they are an exercise that is not directed to the present. The athlete’s mind
is fixed ahead of him, building up his skill; and he vaults in imagination into the future.

Poised for that leap, the pole-vaulter is a capsule of human abilities: the grasp of the hand, the arch of the foot, the muscles of the shoulder and pelvis – the pole itself, in which energy is stored and released like a bow firing an arrow. The radical character in that complex is the sense of foresight,
that is, the ability to fix an objective ahead and rigorously hold his attention on it. The athlete’s performance unfolds a continued plan, from one extreme to the other, it is the invention of the pole, the concentration of the mind at the moment before leaping, which give it the stamp of humanity.

The head is more than a symbolic image of man; it is the seat of foresight and, in that respect,
the spring which drives cultural evolution. Therefore if I am to take the ascent of man back to its beginnings in the animal, it is the evolution of the head and the skull that has to be traced. Unhappily, over the fifty million years or so to be talked about, there are only six or seven essentially distinct skulls which we can identify as stages in that evolution. Buried in the fossil record there
must be many other intermediate steps, some of which will be found; but meanwhile we must conjecture what happened, approximately, by interpolating between the known skulls. The best way to calculate these geometrical transitions from skull to skull is on a computer; so that, in order to trace the continuity, I present them on a computer with a visual display which will lead from one to the next.

Begin fifty million years ago with a small tree-dwelling creature, a lemur; the name, appropriately, is that of the Roman spirits of the dead. The fossil skull belongs to the lemur family
Adapis
, and was found in chalky deposits outside Paris. When the skull is turned upside down, you can see the
foramen magnum
far at the back – this is a creature that hung, not held, its head on the spine. The
likelihood is that it ate insects as well as fruits, and it has more than the thirty-two teeth that man and most primates now have.

The fossil lemur has some essential marks of the primates, that is, the family of monkey, ape and man. From remains of the whole skeleton we know that it has finger nails, not claws. It has a thumb that can be opposed at least in part to the hand. And it has in the
skull two features that really mark the way to the beginning of man. The snout is short; the eyes are large and widely spaced. That means that there has been selection against the sense of smell and in favour of the sense of vision. The eye-sockets are still rather sideways in the skull, on either side of the snout; but compared with the eyes of earlier insect eaters, the lemur’s have begun to
move to the front and to give some stereoscopic vision. These are small signs of an evolutionary development towards the sophisticated structure of the human face; and yet, from that, man begins.