A small point, but one that is relevant here, is that carnivores have fleas but primates do not. Monkeys and apes are plagued by lice and certain other external parasites but, contrary to popular opinion, they are completely flealess, for one very good reason. To understand this, it is necessary to examine the lifecycle of the flea. This insect lays its eggs, not on the body of its host, but amongst the detritus of its victim’s sleeping quarters. The eggs take three days to hatch into small, crawling maggots. These larvae do not feed on blood, but on the waste matter that has accumulated in the dirt of the den or lair. After two weeks they spin a cocoon and pupate. They remain in this dormant condition for approximately two more weeks before emerging as adults, ready to hop on to a suitable host body. So for at least the first month of its life a flea is cut off from its host species. It is clear from this why a nomadic mammal, such as a monkey or ape, is not troubled by fleas. Even if a few stray fleas do happen on to one and mate successfully, their eggs will be left behind as the primate group moves on, and when the pupae hatch there will be no host ‘at home’ to continue the relationship. Fleas are therefore parasites only of animals with a fixed home base, such as the typical carnivores. The significance of this point will become clear in a moment.
In contrasting the different ways of life of the carnivores and the primates, I have naturally concentrated on the typical open-country hunters on the one hand, and the typical forest-dwelling fruit-pickers on the other. There are certain minor exceptions to the general rules on both sides, but we must concentrate now on the one major exception—the naked ape. To what extent was he able to modify himself, to blend his frugivorous heritage with his newly adopted carnivory? Exactly what kind of an animal did this cause him to become?
To start with, he had the wrong kind of sensory equipment for life on the ground. His nose was too weak and his ears not sharp enough. His physique was hopelessly inadequate for arduous endurance tests and for lightning sprints. In personality he was more competitive than co-operative and no doubt poor on planning and concentration. But fortunately he had an excellent brain, already better in terms of general intelligence than that of his carnivore rivals. By bringing his body up into a vertical position, modifying his hands in one way and his feet in another, and by improving his brain still further and using it as hard as he could, he stood a chance.
This is easy to say, but it took a long time to do, and it had all kinds of repercussions on other aspects of his daily life, as we shall see in later chapters. All we need concern ourselves with for the moment is how it was achieved and how it affected his hunting and feeding behaviour.
As the battle was to be won by brain rather than brawn, some kind of dramatic evolutionary step had to be taken to greatly increase his brain-power. What happened was rather odd: the hunting ape became an infantile ape. This evolutionary trick is not unique; it has happened in a number of unique separate cases. Put very simply, it is a process called neoteny) by which certain juvenile or infantile characters are retained and prolonged into adult life. (A famous example is the axolotl, a kind of salamander that may remain a tadpole all its life and is capable of breeding in this condition.)
The way in which this process of neoteny helps the primate brain to grow and develop is best understood if we consider the unborn infant of a typical monkey. Before birth the brain of the monkey foetus increases rapidly in size and complexity. When the animal is born its brain has already attained seventy per cent of its final adult size. The remaining thirty per cent of growth is quickly completed in the first six months of life. Even a young chimpanzee completes its brain growth within twelve months after birth. Our own species, by contrast, has at birth a brain which is only twenty-three per cent of its final adult size. Rapid growth continues for a further six years after birth and the whole growing process is not complete until about the twenty-third year of life.
For you and me, then, brain-growth continues for about ten years after we have attained sexual maturity, but for the chimpanzee it is completed six or seven years before the animal becomes reproductively active. This explains very clearly what is meant by saying that we became infantile apes, but it is essential to qualify this statement. We (or rather, our hunting ape ancestors) became infantile in certain ways, but not in others. The rates of development of our various properties got out of phase. While our reproductive systems raced ahead, our brain-growth dawdled behind. And so it was with various other parts of our make-up, some being greatly slowed down, others a little, and still others not at all. In other words, there was a process of differential infantilism. Once the trend was under way, natural selection would favour the slowing down of any parts of the animal’s make-up that helped it to survive in its hostile and difficult new environment. The brain was not the only part of the body affected: the body posture was also influenced in the same way. An unborn mammal has the axis of its head at right angles to the axis of its trunk. If it were born in this condition its head would point down at the ground as it moved along on all fours, but before birth occurs the head rotates backwards so that its axis is in line with that of the trunk. Then, when it is born and walking along, its head points forwards in the approved manner. If such an animal began to walk along on its hind legs in a vertical posture, its head would point upwards, looking at the sky. For a vertical animal, like the hunting ape, it is important therefore to retain the foetal angle of the head, keeping it at right angles to the body so that, despite the new locomotion position, the head faces forwards. This is, of course, what has happened and, once again, it is an example of neoteny, the pre-birth stage being retained into the post-birth and adult life.
Many of the other special physical characters of the hunting ape can be accounted for in this way: the long slender neck, the flatness of the face, the small size of the teeth and their late eruption, the absence of heavy brow ridges and the non-rotation of the big toe.
The fact that so many separate embryonic characteristics were potentially valuable to the hunting ape in his new role was the evolutionary breakthrough that he needed. In one neotenous stroke he was able to acquire both the brain he needed and the body to go with it. He could run vertically with his hands free to wield weapons, and at the same time he developed the brain that could develop the weapons. More than that, he not only became brainier at manipulating objects, but he also had a longer childhood during which he could learn from his parents and other adults. Infant monkeys and chimpanzees are playful, exploratory and inventive, but this phase dies quickly. The naked ape’s infancy was, in these respects, extended right through into his sexually adult life. There was plenty of time to imitate and learn the special techniques that had been devised by previous generations. His weaknesses as a physical and instinctive hunter could be more than compensated for by his intelligence and his imitative abilities. He could be taught by his parents as no animal had ever been taught before.
But teaching alone was not enough. Genetic assistance was required. Basic biological changes in the nature of the hunting ape had to accompany this process. If one simply took a typical, forest-living, fruit-picking primate of the kind described earlier, and gave it a big brain and a hunting body, it would be difficult for it to become a successful hunting ape without some other modifications. Its basic behaviour patterns would be wrong. It might be able to think things out and plan in a very clever way, but its more fundamental animal urges would be of the wrong type. The teaching would be working against its natural tendencies, not only in its feeding behaviour, but also in its general social, aggressive and sexual behaviour, and in all the other basic behavioural aspects of its earlier primate existence. If genetically controlled changes were not wrought here too, then the new education of the young hunting ape would be an impossibly uphill task. Cultural training can achieve a great deal, but no matter how brilliant the machinery of the higher centres of the brain, it needs a considerable degree of support from the lower regions.
If we look back now at the differences between the typical ‘pure’ carnivore and the typical ‘pure’ primate, we can see how this probably came about. The advanced carnivore separates the actions of food-seeking (hunting and killing) from the actions of eating. They have become two distinct motivational systems with only partial dependence one on the other. This has come about because. the whole sequence is so lengthy and arduous. The act of feeding is too remote, and so the action of killing has to become a reward in itself. Researches with cats have even indicated that the sequence there has become further sub-divided. Catching the prey, killing it, preparing it (plucking it), and eating it, each have their own partially independent motivational systems. If one of these patterns of behaviour is satiated, it does not automatically satiate the others.
For the fruit-picking primate the situation is entirely different. Each feeding sequence, comprising simple food-searching and then immediate eating, is comparatively so brief that no splitting up into separate motivational systems is necessary. This is something that would have to be changed, and changed radically, in the case of the hunting ape. Hunting would have to bring its own reward, it could no longer simply act as an appetitive sequence leading up to the consummatory meal. Perhaps, as in the cat, hunting, killing and preparing the food would each develop their own separate, independent goals, would each become ends in themselves. Each would then have to find expression and one could not be damped down by satisfying another. If we examine—as we shall be doing in a later chapter—the feeding behaviour of present-day naked apes, we shall see that there are plenty of indications that something like this did occur.
In addition to becoming a biological (as opposed to a cultural) killer, the hunting ape also had to modify the timing arrangements of his eating behaviour. Minute by minute snacks were out and big, spaced meals were in. Food storage was practised. A basic tendency to return to a fixed home base had to be built in to the behavioural system. Orientation and homing abilities had to be improved. Defecation had to become a spatially organized pattern of behaviour, a private (carnivore) activity instead of a communal (primate) one.
I mentioned earlier that one outcome of using a fixed home base is that it makes parasitisation by fleas possible. I also said that carnivores have fleas, but primates do not. If the hunting ape was unique amongst primates in having a fixed base, then we would also expect him to break the primate rule concerning fleas, and this certainly seems to be the case. We know that today our species is parasitised by these insects and that we have our own special kind of flea—one that belongs to a different species from other fleas, one that has evolved with us. If it had sufficient time to develop into a new species, then it must have been with us for a very long while indeed, long enough to have been an unwelcome companion right back in our earliest hunting-ape days.
Socially the hunting ape had to increase his urge to communicate and to co-operate with his fellows. Facial expressions and vocalisations had to become more complicated. With the new weapons to hand, he had to develop powerful signals that would inhibit attacks within the social group. On the other hand, with a fixed home base to defend, he had to develop stronger aggressive responses to members of rival groups.
Because of the demands of his new way of life, he had to reduce his powerful primate urge never to leave the main body of the group.
As part of his new-found co-operativeness and because of the erratic nature of the food supply, he had to begin to share out his food. Like the paternal wolves mentioned earlier, the hunting ape males also had to carry food supplies home for the nursing females and their slowly growing young. Paternal behaviour of this kind had to be a new development, for the general rule is that virtually all parental care comes from the mother. (It is only a wise primate, like our hunting ape, that knows its own father.)
Because of the extremely long period of dependency of the young and the heavy demands made by them, the females found themselves almost perpetual) confined to the home base. In this respect the hunting ape’s new way of life threw up a special problem, one that it did not share with the typical ‘pure’ carnivores: the role of the sexes had to become more distinct. The hunting parties, unlike those of the ‘pure’ carnivores, had to become all-male groups. If anything was going to go against the primate grain, it was this. For a virile primate male to go off on a feeding trip and leave his females unprotected from the advances of any other males that might happen to come by, was unheard of. No amount of cultural training could put this right. This was something that demanded a major shift in social behaviour.
The answer was the development of a pair-bond. Male and female hunting apes had to fall in love and remain faithful to one another. This is a common tendency in many other groups of animals, but is rare amongst primates. It solved three problems in one stroke. It meant that the females remained bonded to their individual males and faithful to them while they were away on the hunt. It meant that serious sexual rivalries between the males were reduced. This aided their developing co-operativeness. If they were to hunt together successfully, the weaker males as well as the stronger ones had to play their part. They had to play a central role and could not be thrust to the periphery of society, as happens in so many primate species. What is more, with his newly developed and deadly artificial weapons, the hunting ape male was under strong pressure to reduce any source of disharmony within the tribe. Thirdly, the development of a one-male one-female breeding unit meant that the offspring also benefited. The heavy task of rearing and training the slowly developing young demanded a cohesive family unit. In other groups of animals, whether they are fishes, birds or mammals, when there is too big a burden for one parent to bear alone, we see the development of a powerful pair-bond, tying the male and female parents together throughout the breeding season. This, too, is what occurred in the case of the hunting ape.