Contents Updated: Tuesday, August 24, 1999
Not all of these can be regarded as primary. The importance of walking bipedally is that the hands are freed to manipulate things, making the evolution of a large brain more likely and then toolmaking, art and written communication possible. Which, then, are the primary factors? Naturally different authorities have different emphases. We shall discuss them here to get some clues to indicate what characteristics an intelligent dinosaur might have.
Don Johanson quotes Owen Lovejoy, an expert on locomotion, as stating, from the standpoint of pure efficiency bipedalism is a preposterous way of running. Preposterous? Inefficient? Besides humans, birds find bipedalism a perfectly efficient way of running as did many dinosaurs. Some say it was crucial to the development of mankind. Dr J.Bronowski in The Ascent of Man writes, 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 origin of bipedalism must be seen as one of the major steps, if not the major step, in human evolution, says Richard Leakey, a leading authority on the origins of mankind. He continues, habitually walking around on the hindlimbs, leaving the forelimbs free for other jobs, is an unusual (sic) mode of locomotion. Once our ancestors had adopted an upright stance many things associated with being human became possible, such as fine manipulation with the hands, and the carrying of food back to base camp.
Yet, if bipedalism is so vital to being human and is a new integration of life, and dinosaurs had made this commitment two hundred million years before man, why didn't they develop human characteristics? Is it possible they did?
The change to bipedalism required major changes in our ancestors' anatomy; bones, muscles, internal organs all had to alter. Dinosaurs did not need such drastic modification. They had evolved as bipedal animals. Why did our ancestors become upright? Not so that man could make tools as old fashioned schoolbooks told us. Evolution is not conscious—it cannot think ahead and make arrangements to meet its purposes. Furthermore, man was walking upright two million years before tools were made. The Laetoli footprints and Johanson's discoveries show that primates were walking about fully erect almost four million years ago. The crude stone tools at found at Hadar were possibly 2.5 million years old, but some prefer an age of two million years. Watching for predators is a more likely answer.
Another is to do with feeding habits. Baboons partially sit upright while seeking scattered food items. Perhaps primitive prehominids did the same. Moving about upright would also have allowed food to be carried away to be eaten at leisure safe from predators. Gradually, because it conferred such advantages, they adopted the upright stance permanently. Such arguments emphasize the immense start the dinosaurs had in being upright from the beginning.
Carl Sagan in Dragons of Eden gives four reasons, all to do with the brain, why intelligence in apes emerged only in the last few million years. (1) The brain had to grow bigger than a critical size. (2) The ratio of brain to body mass had to exceed a certain value. (3) The brain had to make more neural connections than before. (4) The brain had to evolve particular functions (in the frontal and temporal lobes perhaps). The first three imply only a quantitative change was needed but the fourth requires qualitative change instead (or as well).
It is plain from the fossil record that in the series of species that led up to man there has been a growth in brain capacity from about 350 cm^3 in the apes to a maximum of about 2000 cm^3 in recent and modern men. The human baby's brain is now so large that mothers often experience difficult and painful childbirth. The English anatomists of Piltdown fame, Woodward and Keith, defined 750 cm^3 as the critical size for intelligence. Later Le Gros Clark reduced it to 700 cm^3. These definitions were purely arbitrary.
Brain size alone is not now regarded as sufficient to define a species—it is too variable. Cranial capacity in people today ranges from 1000 cm^3 to 2000 cm^3. Earlier hominids had brain capacities that overlapped considerably with preceding and succeeding ones. The H.erectus range was 700 to 1250 cm^3, overlapping with the H.sapiens range. The H.habilis range was 500 to 800 cm^3, overlapping that of H.erectus. And Hominid brains only started to get bigger than apes' about two million years ago, apparently concurrently with the making of tools. The range is continuous and offers no basis in itself for deciding when intelligence occurred. What is more, brain size does not correlate with intelligence, though there is a correlation between brain size and body size. Men have larger brains than women because they have larger bodies—but they are no more intelligent than women. When fossil craniums are found that appear the same save for their size, they are likely to differ only in the sex of their owner.
Big brained people are not generally more intelligent than smaller brained people. Our brains seem to have overdeveloped for some reason—only a part is used. The bulk varies in size from person to person but, being unused, does not affect intelligence. A creature with a much smaller brain using it more efficiently might be capable of behavior just as sophisticated as our own.
According to David Attenborough, macaques are one of the most successful and versatile of all primates. Although they have a small brain compared with ours, it is complex and large for their size and they are intelligent and adaptable. Some macaques have become media personalities in the last few decades. A group of Japanese macaques living in the cold mountains of northern Japan found some volcanic springs. Quickly the whole troop learnt how to shelter in the warmth of the hot spring water. In 1953 Japanese scientists were attempting to study a troop of macaques on the small island of Koshimu. To lure them into the open for ease of observation the scientist took to burying sweet potatoes in the sand. The monkeys were troubled by the dirt on the tubers until one female in a flash of gestalt took a tuber to a rock pool and rinsed away the particles of sand. Within a few months the whole troop had spotted and picked up the trick. The same monkey also discovered how to separate rice and sand by throwing the mixture into a pool and skimming off the rice. If the thinking animal's niche were vacant, these monkeys could evolve into it over the next few million years—and they might still have the chance!
A bigger brained animal will be more intelligent than a smaller brained one, all else being equal. But since all else is not equal, we cannot be definite about a threshold brain size for intelligence.
A better criterion of intelligence might be the ratio of the brain's weight to that of the whole body. This allows for the tendency of larger creatures to have larger brains simply to regulate their larger bodies. Sagan gives the ratio of body to brain weights for the Hominids as: 90 for A.robustus; 50 for A.africanus; 60 for H.habilis; 65 for H.erectus; 45 for H.sapiens. There seems to have been no significant decrease in this ratio since A.africanus and indeed the early toolmaking hominids seem to have had smaller brains for their body size than the non-toolmaking A.africanus. A.robustus, if descended from A.africanus, obviously regressed considerably—though there is some margin of error in these ratios. More importantly, the European pygmy shrew with a body weight of 4.7 grams and a brain weight of 0.1 grams has a body to brain weight ratio of 47, very similar to our own. On this criterion pygmy shrews should be as intelligent as us! Evidently it is no criterion.
Sagan's two remaining criteria, the quantitative change in the number of neural connections leading on to the qualitative change needed for the development of different specialisms by the brain are probably more relevant. Regrettably, these are not easy to measure, though some clues can be had from casts of the interior of skulls. Bulges in certain parts of the brain can be related to the development of certain functions—like speech.
According to the biologist, George Gaylord Simpson, speech is the single most diagnostic trait of mankind. David Attenborough writes: Man's passion to communicate and to receive communications seems as central to his success as a species as the fin was to the fish or the feather to the birds. Speech itself leaves no fossil records but we noted that the development of the lobes of the brain gives some clues. The part responsible for speech is Broca's area. All the hominids have a swollen Broca's area though it is most pronounced in man. Even in chimpanzees there is evidence of swelling here, suggesting a growth in conscious articulation.
The shape of upper and lower mandibles also can give clues because of their need to accommodate the speaking mammal's unusual tongue.
Speech seems to be recent. Arguably it started as long as 100,000 years ago but did not become well developed until 45,000 years ago. Rational thinking that is purely verbal is probably only tens or hundreds of thousands of years old, Robert Bakker tells us. Were people before then not human? No one has any real idea how or why speech evolved. People have no need to speak to make tools, to hunt or to draw pictures. Our best guess is that it develops as a form of social cement for intelligent and social creatures that have largely lost their sense of smell and are close to developing the formalized social structures that become civilization. It is a derivative of and a symptom of intelligence rather than a factor in its birth.
Is extended parental care the essential ingredient? There are two extreme strategies for propagation of the species. One requires the laying and distribution of many small eggs which the parents leave to their own devices knowing that a few will survive. Let us call this the negligent strategy. In the other a lot of parental energy and attention is devoted to the few eggs and offspring they produce. Let us call the latter the indulgent strategy. Though the negligent approach is more common for less complicated life forms, the higher life forms are not the only caring parents. Even some fish build nests and protect their young, by hiding them in their mouths, for example.
Cold-blooded turtles adopt the negligent approach. They lay large numbers of eggs on a remote beach then swim off leaving the hatchlings to fend for themselves. But cold-blooded alligators build a nest mound for their eggs, guard it, help the hatchlings to free themselves then protect them in a nursery as they grow—an indulgent strategy. Dinosaurs did not produce many eggs indicating an indulgent strategy, and were at least as attentive parents as alligators. The higher primates have taken the indulgent strategy to its ultimate conclusion. They have only single young, very infrequently, and spend a lot of parental time and energy in raising them—chimpanzees have one child every five years only. Primate parents have a lot of responsibility and need to be resourceful—natural selection has therefore strongly favored intelligence. Perhaps this is the really crucial factor in human development?
Yet an extremely indulgent strategy is hazardous. Disease and misfortune to parents or young can be disastrous, despite any amount of parental care. When a child is dependent on its parents for a long time, the death of a parent can be the death of the child. If the child dies the parents have wasted a lot of their resources and energy and have to start the slow process again. The indulgent strategy has not been successful for the great apes. Today all apes except man have small populations in narrow geographical ranges on the verge of extinction.
Why should it have succeeded for humans? Anthropologist, Owen Lovejoy believes that bipedalism was the key to a successful modification of the indulgent strategy by mankind. By learning to walk bipedally the human female was no longer restricted to only one child at a time as were the other apes. She could gather food for herself and he older children while nurturing her baby. The change was drastic enough to trigger the evolution of a train of complementary features—continuous ovulation, pair bonding, sexual attraction between individuals, parental care, intelligence, need for larger brain at birth, need for learning, longer childhood, social grouping and toolmaking. The emergence of each trait stimulated the evolution of others in a complicated evolutionary pattern.
But in the sense that parental nurturing and care is longer and more intensive in humans than in any other primates, humans adopt the ultimately indulgent strategy. The other primates were not successful but mankind is. Lovejoy's explanation is that the human strategy is less indulgent than the apes'. But, if being able to cope with more than one demanding child at a time makes the strategy less extreme than in other primates, it has surely only become true since human beings took to gardening 10,000 years ago. The hunter gatherers remaining today, like the T'Kung of South West Africa, have a reproductive strategy similar to that of the savannah apes. Hunter-gatherer women do not ovulate while the previous child is still suckling and cannot become pregnant while suckling a child. But T'Kung women suckle their children until they are four years' old by which time the child, though still dependent on parental support, is able to begin to help with the gathering. Thus the natural interval between successive children in human hunter gatherer females does not differ greatly from the chimpanzee's. But the care invested in each offspring by humans is much higher because it takes much longer for a human baby to become independent. Human precursors had a more extremely indulgent strategy than the other great apes not a lesser one.
Furthermore some of the other characteristics of intelligence seem to depend heavily on a highly indulgent strategy. Purposefulness, creativity and imagination; thinking ahead, anticipating and predicting are all qualities which may be partly innate but need stimulation and teaching to develop. Attentive parents and a close social organization are necessary for this. For humans, if the degree of indulgence has fallen at all, it has only been since agriculture was invented. Having left the Garden of Eden human females stopped suckling earlier and lost the natural contraceptive protection that went with it. A natural restriction on the growth of population had been removed. Civilized women do not suckle their children at all. They feed their children on the milk of domestic animals. The result is that they begin to ovulate immediately and can be pregnant again within 12 months. After the loss of natural contraception and before artificial contraception was introduced, human females probably had three or four times as many children as they would have had naturally. So it is hardly surprising then that population should have exploded in the last 10,000 years.
One feature of human beings appears to be unique. It is the menopause. Humans are the only animal in which female fertility shuts down while they are still capable of having children. Most women stop producing eggs between 40 and 50, while they are still in the prime of life. Why? One theory is that it is a mistake. Women, through the stresses of civilisation have started to do this in error. The answer is hormone replacement therapy, which allows them to continue as before.
An alternative idea is that the menopause is an evolutionary adaptation that confers survival benefits on to the species. Alan Rogers of the University of Utah, has developed mathematical models which confirm the usefulness of the strategy. The idea is essentially that there is more advantage in a middle aged woman not having more children of her own but helping her own children and their children.. Once a new child is going to take more than three years requiring mother's attention, then the advantage of having grandma comes clearly into the equation. Furthermore, when it is considered that the grandma's children, if she continued to have them, were increasingly likely to be left motherless before they reached adulthood, the selective pressure is still higher.
The reason for the evolution of human menopause is because human children need long and costly parental attention to bring them to maturity and so older women cannot continue to have children which she might not be able to see through to maturity but instead helps the survival of her own line by supporting her daughters.
Contrary to this Mormon idea however is the evidence of primitive societies that post menopausal women, far from taking on a granny role, become important figures in their societies. These women seem not to have the hot flushes and other menopausal symptoms of western women. One reason for this might be their higher levels of prolactin and oxymycin from breast feeding continually. Such women certainly do not have the negative feelings of lost youth felt by western women and display it often in a gusto for sex without concern. Menopause is therefore truly the natural contraceptive which evolved to let the labourers have some fun later in life!
The people of old knew that breast-feeding delayed the next conception. Modern researches have shown that the key is the length of time the baby spends suckling. Unfortunately, this varies considerably from one mother and child pair to another and there seems to be no rules. Some babies feed quickly and efficiently, completing their suckling in seven minutes and feeding only about seven times a day. Other babies need 30 minutes a time and demand feeding more often. The only sensible action to be taken is not to offer food other than breast milk. Supplementary foods can plainly make the baby less demanding at the breast and will therefore be likely to permit menstruation and another pregnancy. Some women were fertile again in 10 weeks while others lasted out 70 weeks. If mothers have a baby keen on suckling, they can expect not to menstruate for six months after their previous birth.
Menstruation is, of course, the sign that fertility has returned but when suckling ceases or falls off enough, fertility can return remarkably quickly. Women who wean their babies suddenly can become fertile in days, it seems.
Trouble breast feeding is usually nothing physiological but is brought about by the stress of modern hospital births that can inhibit the release of the hormone, oxytocin, which permits the release of milk from the breast. This hormone and prolactin, which stimulates milk production, are not immediately produced at birth because steroid hormone levels, high during pregnancy, have to fall first. Thus newly born babies suckle at unproductive breasts and are often given supplements while the breast milk flow improves. This is wrong. The suckling stimulates the milk flow. Lack of suckling through excessive concern to feed the infant supplements before milk is being properly produced actually will inhibit proper milk flow.
Furthermore, the supplements will affect the baby's ability to regulate its own glucose levels, with later consequences. The brief period when the child cannot feed properly gives its own body a chance to regulate the conversion of storage hydrocarbon, glycogen, into glucose.
Suckling prevents fertility in the mother by disrupting the hourly release of a regulatory hormone GNRH (gonadotrophin releasing hormone) from the brain's hypothalamus. The regular pulses are not fully stopped but their irregularity prevents the release of another hormone from the pituitary gland which stimulates the maturing of an egg. The monthly egg therefore does not grow. When suckling falls off below a certain level, the regular pulsing of GNRH suddenly reappears.
Cooperation developed from the longer dependency of human young on their mother. A division of labor occurred. The females, responsible for bringing up the children, undertook the placid activity of gathering, providing a degree of security and the group's reliable food supplies. The males, with less responsibility and able to risk their security, sought to get the richer animal protein, initially through scavenging for animal remains and later by actively hunting. But it was not how the food was obtained that triggered the emergence of mankind but the joint manner in which food was eaten and the cementing of social bonds that it entailed. While gathering, the females shared her food and her experience with her children, male and female. Males, used to sharing with their mothers, brothers and sisters, gradually adopted it as adults realizing that sharing provided more secure returns than individual prospecting. The sharing culture spread and eventually societies became more cooperative rather than purely competitive.
Baboons do not share although they do forage together. Chimps rarely share and when they do it is normally after prolonged scrounging. The habit acquired by human males from their mothers, of sharing food, distinguished humans from other primates where the dominant male was more likely to steal it, and led to cooperation and economic interdependence.
Hunting and tool making were luxuries that could be enjoyed because the females provided a secure base for the human group through food gathering. Even the first tools—sticks for reaching and digging, stones for cracking nuts, sharp stones for cutting roots, and bark for containers—might have been made by women to assist gathering. The technological invention that led to mankind might not have been the hand axe used by the hunters but rather the container which allowed a lot of food items to be collected by the gatherers, the women and children, and transported back to base for communal eating later.
Several million years ago several environmental niches were filled by clever and adventurous primates. Chimpanzees, being woodland animals, mainly ate fruit. Baboons, like men, had moved on to the savannah and lived on roots, grass and seeds (both baboons and chimpanzees ate meat but it constituted only five per cent of their diet). The savannah apes had a similar territory and diet to the baboons but had discovered new strategies. The division of labor and sharing freed their males to spend more time getting meat. Gathering would continue to give the communes of apes reliable basic sustenance, but scavenging and then hunting provided concentrated protein. This was a vital step forward giving the apes time to think, and later time to philosophize.
Herbivorous elephants have to spend three quarters of their time eating their low quality food. The carnivorous lion on the other hand only spends about 15 per cent of its time seeking and eating its food rich in protein.
The step to scavenging was fairly easy. There was always some recently dead creature not far away on the savannah and the alert apes would have noticed circling vultures. At Sterkfontein in South Africa, Elisabeth Vrba and Philip Tobias found accumulations of savannah ape bones apparently collected by a predator (possibly a leopard) in its den. There were no stone tools in that layer but in a higher and more recent layer there were stone tools and a pattern of animal remains typical of a scavenger. It seems that the scavenger (Homo habilis) was a toolmaker while his predecessor who made no tools (A.africanus) was prey. From scavenging it was not such a large step for the emergent men to appreciate that carcasses could be created.
Sherwood Washburn in 1956 argued that hunting was the key to human development. Washburn reasoned that, because the apes were slow they had to substitute cunning and cooperation for speed. The new art of hunting in groups required an effective means of communication at a distance: the development of language was the result. The hunting theory of Washburn became accentuated into the theory of the killer ape promoted by Robert Ardrey. Robert Ardrey says, Man is man and not a chimpanzee, because for millions upon millions of years we killed for a living. But killing for a living cannot have led to speech. Shouting to companions is the last thing that a hunter would do if he did not want his prey to bolt, and speaking arose too late to have been triggered by hunting millions of years before.
The contentment of the hunter-gatherers and their sensitivity to their environment belies the hunting hypothesis of human aggressiveness. The hunter-gatherer way of life is not one of grinding insecurity, incessant toil and hardship. It offers as much, if not more, leisure than people have today. Hunter gatherer communities have total confidence in their ability to obtain sustenance from their environment and feel no need to store or save for the long term. Though it no longer appeals to us, pampered by our advanced technology, hunter-gathering is comfortable and secure to those brought up to it. Moreover, many of today's hunter-gatherers like the San of South West Africa have been forced by gardeners and farmers into harsh environments on the margins of deserts. They comfortably survive, but, before they were thrust to the desert margins, the hunter-gatherers would have had much lusher pickings. It is no exaggeration to call it the Garden of Eden—all was provided simply by reaching out or digging up a root.
Marshall Sahlins who has studied stone age economics in depth assures us all people's wants are easily satisfied. Males of the T'Kung hunt for only 21 hours a week and the women (who provide two thirds of the food) gather for only 12 hours. In terrain which to us is inhospitable desert, they have sufficient.
Richard Leakey thinks our aggression may be a pathological response to the human condition that has emerged since the first urban communities of 10,000 years ago. He writes, for perhaps two million years, human ancestors had practised nomadic hunting-and-gathering, in a way of life that was characterized by stability rather than change in terms of technology and culture. Then the ancient way of life was virtually abandoned over a period of a few thousand years. We may be still suffering the trauma of that immense change.
But mankind hunted animals to extinction long before we were shown the gate of the Garden of Eden. Of the savannah apes, the steps to scavenging and hunting were too great for A.robustus. They did not realize the value of meat or, if they did, they found competition with Homo and the baboons too difficult. Homo forced them to eat less nutritious food needing a lot of processing. They evolved jaws suitable for low grade food but were marginalized by their proto-human rivals, became their prey and were pushed into extinction. Were our insensitivity to the other inhabitants of the Garden, our incompetence as custodians and our genocidal destructiveness the reasons for our expulsion? Have present day hunter-gatherers been marginalized precisely because they are not aggressive enough?
A killer instinct is possibly a contributory factor to world domination, generating a particularly aggressive competitiveness that has been partly instrumental in mankind's progress. Of course, many dinosaurs were savage killers too—our killer instinct might be part of our dinosaur heritage.
This survey suggests some factors that influenced the emergence of the intelligent mammal. They are: manipulative forelimbs with grasping fingers and opposable thumbs; binocular vision; color vision; omnivorous diet; curiosity and opportunism; upright posture; exceptionally lengthy childhood dependence on parental care enabling teaching to occur with development of higher skills and creativity; large brain; toolmaking; sharing, division of labor and cooperation; aggression and a callous indifference to other species, as well as other humans, fostered by hunting. Have the dinosaurs of 70 million years ago left any signs of their having any of these characteristics? I shall explore this in the next chapter.