Return to the Brain of Eden

FROM THE FOREST

The left-in-the-dark theory that we will unfold more fully in this and the next chapter offers persuasive new explanations for the rapid enlargement of the human brain, our hairlessness, the length of our childhood, why we walk on two legs, and our aggressive nature—questions that have perplexed researchers since Darwin. Strong evidence is also presented that shows that for a crucial period of our evolutionary history, our distant human ancestors were primarily forest-dwelling fruit eaters, not animal hunters, as is commonly supposed. The study of research data on archaeology, primate nutrition, and human anatomy all point to the same startling conclusion.

Primates evolved, diversified, came, went, lived, still live, reproduced, and ate in the forest. Primates have arboreal origins, and in the very distant past, the lineage that gave rise eventually to the higher apes switched its diet from an insect-based one to one based on flowers, leaves, shoots, nuts, and fruit. This may have happened in the region of seventy million years ago. Primates in general have certain traits that include a larger brain-to-body ratio than most other mammals. Can this be linked to this change of diet?

Other groups of animals show a similar correlation. Fruit bats have a larger brain-body ratio than their insect-eating relatives (up to twice the brain size), and so do parrots. The intelligence of these birds has led researchers to jokingly classify them as “honorary primates” because their ability to categorize objects and grasp abstract concepts like the similarity of shapes and colors rivals that of chimpanzees. Species of primates that have a high percentage of fruit in their diet tend to have proportionately larger brains than do their cousins that eat a more leafy or omnivorous diet. These examples clearly show that changing from an insect-based diet to a fruit-based one is linked to an increase in brain size.

The primates that ate more fruit and came to depend on fruit would, of course, have to live in the forest because this is where fruit grows. In the warm, wet climate of the tropics, there is little seasonal variation, so trees such as figs could (and still do) provide fruit all the year round. Along with nectar, fruit by its very nature is a “free lunch” provided by the plant kingdom. It is designed to be eaten, its quality as a food is a reward for seed dissemination, and it can be gathered with relatively little effort. It is the most obvious food source for primates and hominids, and as we will detail later, the fossil evidence of hominid dentition strongly suggests fruit was the most important element in their diet. Fruit is a very good food source. It is rich in nutritive value, easily digested, and low in toxicity. The normal mechanisms of evolution would have acted on both primate and tree species so that they became adapted to a life of symbiotic interdependence.

It is of benefit to the fruit trees to make the fruit as healthy a food as possible. Healthy primates mean better seed dissemination; thus there may have been a degree of coevolution at work here. If certain fruit, for instance a variety of fig, not only tasted better but also made the hominid feel better, then this variety would have been selected more often and hence dispersed more efficiently. (This scenario is entirely plausible, for figs contain chemicals that elevate neurotransmitter activity, which can in turn affect a hominid’s mental state.) If the chemicals in the fruit also enhanced neural expansion, a feedback mechanism may have been initiated; more fruit means more fruit biochemistry means more neural expansion and more fruit dispersal. Selecting only the more powerfully loaded fruits would fuel this process even more. The hominids may have unwittingly managed the forest environment by selecting and dispersing the most beneficial fruits. With more chemically rich fruit available, there would be more fuel to act on the hominid’s neural system. A mechanism such as this could have led to a very rapid evolutionary leap.

There would have been dozens of different lineages and dozens of branches on the primate tree of evolution; some are known, some are waiting to be discovered, and probably many more will be forever lost in the mists of time. But the key ingredient on the branch or group of branches that lead to the hominid line was a dietary specialization on fruit, and this necessitated a life in the forest. Unfortunately for the hominid researcher, animals do not tend to fossilize in tropical forest environments. This is a point worth emphasizing. If no fossilized hominids have been found in tropical forest environments, it does not mean they were not there. No fossilized chimps and bonobos have been found in this environment either, and they definitely were there, and still are, eating a mainly fruit- and plant-based diet.

HUMAN EVOLUTION

The current model of human evolution is based on a very limited number of fossil finds, while the fossil record of the great ape ancestry is almost entirely absent. (In fact, there is not enough fossil evidence from human and hominid lines to categorically prove this or any other hypothesis of human evolution.) This gives credence to the hypothesis that the fossil remains of hominids that have been discovered represent populations that left the forest, but it in no way discounts the notion that a source population remained in the forest. If no remains of the forest apes survived as fossils, why should remains of forest humans? The fossil remains that we do have are likely to represent humans that had spent many generations out of their optimal environment and as such cannot give a true representation of what was really happening in the forest. The rather simplistic theory of hominid descent, which is implied rather than stated, is that the ramapithecines were the ancestors of the australopithecines that were the ancestors of the Homo line. Within the Homo line there was Homo habilis, that was the ancestor to Homo erectus, that in turn was the ancestor of Homo sapiens; “A” leads to “B” leads to “C,” and so on. We suggest another pattern that maintains an evolving population within the prime forest area from which offshoots emerge. Species A in the forest evolves into species B, which remains in the forest, but an offshoot of species A emerges onto the savannah, and its remains are fossilized and later given the name Ramapithecus. An offshoot of species B leaves the forest, and its fossilized remains are given the name Australopithecus. Thus the few fossil remains of hominids that have been discovered represent waves of evolutionary “dead ends” (as far as continuing brain expansion is concerned) that left the forest. Many different lines of temporarily successful hominids could have followed this evolutionary route. Meanwhile the hominid lineage that lead to Homo sapiens continued to develop back in the fruit-rich, leafy, and womblike environment.

We propose that from the earliest days of primate fruit eating, the chemicals included in the diet started to short-circuit the normal evolutionary mechanism. The chemical cocktail that is present in fruit started to modify the way our genetic blueprint was actually read and interpreted. (This process is known as transcribing or transcription.) Powerful biofeedback loops were created that affected assimilation and biochemical function. DNA transcription would have been affected directly, very gradually at first, but at some later point a critical mass was reached that initiated rapid and profound changes. Juvenility was extended, and brain size increased markedly as a result of this new biochemistry.

This was not merely a nutritional effect that fluctuated with season and whim. A specialist fruit diet provided a small but constant flow of these active biochemicals. They were present all the time, through countless generations, and, significantly, the chemicals would have influenced fetal development during pregnancy. As far as the primate’s internal chemistry was concerned, it could have been an internal gland producing these physiology-changing chemicals, for they were so continually present.

These primates were plugged into the tree biochemistry— continuously and over millions of years. (External estrogen-like chemicals in our present environment are causing biochemical changes in both humans and other animals today. This is a similar effect, and it confirms this mechanism is not merely theoretical. For example, some river fish have been found to become hermaphrodites in response to pesticide runoff, and it is possible that the sperm count in men is dropping due to residues of birth control pills that end up in our water supplies.)

Each genetic line would respond to this continual biochemical intake in a different way. Each line would be unique—a subtle variation on the model. There could have been hundreds of genetic starting points and hundreds of different outcomes. Specializing in fruit eating is not a magical route that is going to automatically result in the development of a brainy superhominid. But as traits such as increased brain size and extended juvenility are seen to a greater or lesser extent in the higher apes as well as hominids, it appears that the correlation between brain size and fruit eating is strong.

JUVENILITY AND BIPEDALISM

The continual assimilation of the chemicals found in tropical fruits would have had a direct affect on the mechanisms of juvenility. If there were an inhibition of the internal mammalian hormones that normally build up to a level that triggers sexual maturation, profound and rapid change could have occurred. If, for instance, sexual maturity were delayed for a year or two, a very different animal would emerge, for the whole neuroendocrine system would have had a longer period to grow and develop beyond its previous parameter. This hominid with a longer juvenile period would be different from its ancestor that didn’t eat this chemically rich diet. Though the neuroendocrine system (the system ultimately controlled by the brain that produces hormones) itself plays a central role in the regulation of juvenility, the forest fruit, we hypothesize, introduced a gremlin into the works. It effectively caused an extension of the juvenile period as well as changing the very mechanism that regulated the juvenile period. This led to a fast track of evolutionary change.

Could this have actually happened? The evidence suggests that it may have done. We know that within humans today, the period of rapid brain development ends at puberty. It would have been no different in our distant past. We also know that the chemicals present in fruit have the ability to suppress the steroids that induce sexual maturation. Thus their action could have created a window of opportunity for additional brain development. This would have resulted in a primate with a modified neuroendocrine system, for a bigger or more developed brain would run this system in a slightly different way. The progeny from this hominid with the bigger brain would in turn have been exposed to a changed internal chemical regime. Not only would the fetus have been exposed to a changed environment in the uterus—because its mother has a modified neuroendocrine system—but also the resulting brain itself would have pumped a slightly different complex of chemical messengers. The effect, therefore, could have built with every succeeding generation, creating a lineage with an increasingly modified biochemistry, which would have built individuals with an increasingly different structure and function, even though there would have been no change in the DNA codes.

So the diet of forest hominids could indeed have caused an extension of the juvenile period, and this would have allowed a longer period in which the brain could grow and develop, which would presumably have provided the scope for the enhancement of function. The pressures and opportunities that resulted from these primary changes would have led to other adaptive developments. A longer juvenile phase could have led to an increase in height because the major period of bone growth and particularly bone lengthening occurs at this time. And this may have had further consequences; an arboreal lifestyle could have been progressively restricted because a taller, longer-boned hominid would not have been quite so agile in the trees.

A bigger brain would have needed more time to develop in the uterus before it could function outside; thus we can speculate that there would have been an extension of the gestation period, too. A bigger brain would have led to a bigger head size, but head size couldn’t increase beyond the limits imposed by the restrictions of the birthing process. So a maximum gestation period would have been reached. If the gestation period became any longer and the fetus any larger, the birthing process would no longer be feasible. (As it is, humans appear to have more difficulty giving birth than other animals.) But with such a large and complex brain, this available period of gestation would not have been long enough to complete the brain’s development. In the higher hominids, this would have led to a situation in which the infant’s brain would not have been fully functional at birth. At birth, the infant would have still been in a prenatal state that would have necessitated an increased level of maternal care. This would have created behavioral and physiological pressures. These pressures would have been present to some degree in the early, smaller hominids, but they would have been increasingly significant as body and brain size increased.

The period of pregnancy, the size of the baby, and its helplessness at birth and for an extended period of time thereafter would have put many demands not only on the mother but, in effect, on the whole troupe or social group as well. Solutions to these pressures may have been varied, but in one or more lines of hominids, bipedalism may have been an answer. Standing and walking upright may have been a response to dealing with the extended postnatal stage. Uniquely in the later hominids and especially in humans, the fetal stage in effect continues after birth. A large, helpless baby needs to be looked after and protected. It would have become increasingly difficult for the mother to carry this helpless and growing child around in the trees, so a sustained period on the forest floor may have been a likely option. Because human babies are helpless for so much longer than the infants of closely related primates, they are proportionately more demanding for longer. Solutions to this enforced ground-dwelling phase need not have included bipedalism, but this mode of locomotion does have some advantages in these circumstances. And almost certainly it was a necessary precursor to maximum brain expansion. It is not the only solution, however; chimpanzees sometimes walk rather inefficiently on two legs part of the time, so partial bipedalism or continued four-legged locomotion would have been the preference of some primates. But becoming upright could have been an efficient solution to a burgeoning problem. Walking on two legs frees up both arms to carry the infant. It increases the visual range, which is a helpful adaptation on the less secure forest floor, and it allows both hands (in the case of the mother, one hand) to be used for foraging.

Bipedalism may have even been a response to a flooded forest floor. The Congo River basin, the home to our closest living relatives, has areas that become seasonally inundated with water. The Amazon, the Congo’s sister system in South America, has a total forested area the size of Great Britain that is flooded for six months of the year. Could such a habitat have provided an impetus toward walking upright? Elaine Morgan, in her thought-provoking book Scars of Evolution, sets out the case for an aquatic phase in the evolution of hominids. The so-called aquatic ape theory does have some elements that are intriguing, though more for the questions it raises rather than its ultimate conclusions. For instance, Morgan identifies many of the structural and functional problems of walking with a perpendicular spine (spinal compression, back pain, inguinal hernia, varicose veins, and hemorrhoids) that would be partially ameliorated by spending large amounts of time wading in water. She then goes on to point out:

Walking erect in flooded terrain was less an option than a necessity. The behavioural reward—being able to walk and breathe at the same time—was instantly available. And most of the disadvantages of bipedalism were canceled out. Erect posture imposes no strain on the spine under conditions of head-out immersion in water. There is no added weight on the lumbar vertebrae. The discs are not vertically compressed. (An astronaut in zero gravity gains an inch in height in the first days in space, and immersion in water is the nearest thing to zero gravity on planet Earth.)

In water, walking on two legs incurs no more danger of tripping over and crashing to the ground than walking on four. There is no distension of the veins because immersion in water prevents the blood from pooling in the lower limbs. Water, thus, seems to be the only element in which bipedalism for the beginner may have been at the same time compulsory and relatively free of unwelcome physical consequences. (Morgan 1991)

If the pressures we alluded to earlier were forcing our hominid lineage to spend more time on the forest floor and that forest floor was flooded for part of the year, perhaps there was a need to wade through water to access the fruit trees within their territory. But could this provide a pressure that resulted in bipedalism? We feel it is unlikely, though undoubtedly an upright stance would be of benefit in these circumstances. The theory perhaps makes more sense than the orthodox view, which tries to bamboozle us into believing that, several million years ago, a population of apes or early hominids, living on the savannah, chose to stumble around on two limbs instead of running easily, like chimps and baboons, on four. Morgan asks why they would have “stood up, with their unmodified pelves, their inappropriate single-arched spines, their absurdly under-muscled thighs and buttocks, and their heads stuck on at the wrong angle, and doggedly shuffled along on the sides of their long-toed, ill-adapted feet” (Morgan 1991).

The reasons proposed for this unlikely transition—that we stood up to hunt meat, pick grass seeds, carry food back to our families, or minimize the area of our bodies we exposed to the sun—do not stand any serious scrutiny. The two free arms would have been useful to carry food and a large and helpless infant, and the erect posture may have helped to spot savannah predators, but these advantages are likely to have been a secondary benefit, not the driving force. We also know that bipedalism became a specialized feature of hominids not in the later stages of their evolution but as far back as four million years ago. The “Lucy” skeleton, one of the best-known species of early hominid, Australopithecus afarensis, has been characterized as a “bipedal chimpanzee,” and work in Kenya has unearthed an even earlier species of bipedal hominid known as Australopithecus anamensis. The structure of the pelvis and the knee joints of Lucy and her cousins show that they were upright walkers, but the length of their limbs and the structure of their hands and feet also attest to their arboreal nature. These early hominids were perhaps less adept in the trees than present-day apes and less efficient bipeds than an Olympic sprinter; yet this “halfway house” was successful, for this adaptation endured for some two million years. These early hominids were living in the forest and eating a diet probably not dissimilar to that of chimpanzees and bonobos, and the elements of that diet were found primarily in the forest canopy.

The veracity of this scenario has been strengthened by the finds at Kapsomin in Kenya’s Baringo district. In December 2000 the Kenya Paleontology Expedition reported the discovery of what is almost certainly a new species of hominid. The excavating team, which included Martin Pickford from the expedition and Brigitte Senut from the National Museum of Natural History in Paris, unearthed thirteen fossils belonging to at least five individuals, both male and female. These finds represent a hominid that is far older than any other previous discovery. They have been tentatively dated as at least six million years old, which means they would be some one and a half million years older than Australopithecus anamensis, the previous most ancient hominid, and older than Lucy, too (Senut 2001).

This new hominid has been popularly dubbed “Millennium Man,” but its Linnaean name, Orrorin tugenensis, attests to its discovery in the Tugen Hills. What is most exciting about the find, however, is the creature’s structure. An almost perfectly fossilized left femur shows Millennium Man had strong back legs that enabled it to walk upright, giving it hominid characteristics that relate it directly to the bipedal lineages. The postcranial evidence also suggests that Orrorin tugenensis was already adapted to habitual or perhaps even obligate bipedalism when on the ground. A thick right humerus bone from the upper arm points to its considerable tree-climbing skills, and the length of the fossil bones shows the creature was about the size of a modern chimpanzee. The teeth and jaw structure suggests a similar dentition to modern man. It had small canines and full molars, which indicate that it would have eaten a diet of mainly fruit and vegetables.

Preliminary analyses therefore indicate that the hominid was about the size of a chimpanzee, was an agile climber, walked on two legs when on the ground, and ate a diet of fruit and vegetable matter. Although it is easy to fall into the trap of extrapolating from minimal fossil finds, this outstanding discovery does strongly support our hypothesis that bipedalism developed in the forest in an animal that was an agile tree climber and ate a diet of primarily fruit and leaves.

Further studies of orangutans by Professor Robin Crompton of the University of Liverpool also indicate that the first stages of bipedalism developed in the trees. He has looked in detail at the ways these large primates move along branches and has noted similarities between their gait and the gait of fully functioning bipeds (Thorpe, Crompton et al. 2007). This work, together with the associated evidence we have noted, strongly suggests that the initial stages toward bipedalism arose in the trees and the other pressures that we have identified encouraged the process on toward a fully functional two-legged gait.

Pressures acting on the infant stage may have further propelled bipedalism. Apes can climb from a very young age, but human infants are very different. After a long period of being completely dependent on their mothers, there is a period in which they are more independent but not developed enough to climb on their own. This would have provided a window of opportunity for the infant to experiment with different modes of locomotion. It may have been of great benefit for the young child to develop an efficient way of getting around during the increasingly longer period before it had the strength and dexterity to climb into the trees. And successful children would have survived better and passed their traits to their children. If we look at the way children develop their motor skills today, we can see that they are not strong or balanced enough to climb until well past the age they struggle to become upright. In the context of our arboreal origins, it is worth pointing out that even today, as adults, we still possess impressive climbing abilities. In the rainforests people regularly climb trees to gather honey and fruit. In developed societies, too, many people enjoy climbing as a sport, and gymnasts, particularly on the parallel bars, display superb arboreal skills.

The points we would like to emphasize in all this are that bipedalism developed within the forest and the primary instigating factors were the changes brought about by the biochemistry of the diet. The developmental window would have become longer as the juvenile period extended. Initially there may have been an enforced two or three months on the ground, but as the biochemical changes took effect, this may have been extended to a period of one, two, or even three years. The hominid’s arboreal features would have been retained as much as possible, but these would have been progressively constrained by the hominid’s increasing size. We can see, then, that this change did not come through the normal DNA selection route but via physiological changes brought about by the action of the chemicals contained in the diet.

HAIRLESSNESS AND VITAMIN D

It is all too easy to assume a simplistic picture of human evolution. The story goes that we separated from our nearest relatives, the chimps and bonobos, somewhere around seven million years ago and this line led via various strands of hominids to the Neanderthals and us. The true scenario was in all probability much more complex and fragmented.

Various lineages would have branched off, moved away from the forest, migrated, settled along coastlines, lived, and eventually died out. There may have been back-crossings, for different lineages would certainly have been genetically compatible for a long time. Llamas and camels, separated by five million years of evolution, are still able to interbreed; these hominid lines would have been much closer. Some evidence of human-Neanderthal interbreeding has been suggested from finds in southern Spain. Thus we can safely speculate that different races of hominids would have changed physiologically and then by crossbreeding returned to nearer the hypothetical source population. A highly complicated weaving of strains would have occurred that would have clouded and confused the picture of human ancestry. But at least one lineage would have remained in the forest; after all this was the safest and most nurturing habitat to dwell in. These populations would continue to be subjected to the physical and biochemical pressures imposed by this hothouse environment. Inevitably, over time, further changes would have occurred, and one change may have been a result of the necessity to increase the efficiency of vitamin D absorption. There has been a great deal of confusion about our hairlessness. Why should Homo sapiens be so lacking in body hair? Even Charles Darwin could see no advantage of nakedness to man. The Father of Evolution concluded that “our bodies could not have been divested of hair through natural selection,” but somewhere along the line this is presumably what indeed did happen.

Ideas to explain our nakedness have included a deterrent to parasites, a cooling system, a lure to increase our attractiveness to the opposite sex, and a response to living mainly in water. None of these explanations is particularly convincing. Hairlessness has not deterred ticks and leeches. In hot scenarios fur actually protects against the sun, and in the open savannah, where this is supposed to have taken place, fur would be needed for warmth at night. And no other primate has lost its hair, certainly not as a sexual adornment. The water theory may have more substance. Parallels have been drawn with large aquatic mammals that have developed layers of blubber under a smooth, hairless, or closely furred skin. We do indeed have fat tissue beneath our skin, but fat just wouldn’t have been an issue for a hominid living on a diet of mainly fruit. It is difficult to get fat on a diet of wild fruit. Most of the enlargement of the human blubber layer is a symptom of overeating, which is increasingly easy on a diet of particularly refined carbohydrates.

Did our ancestors, then, really spend eons living in water? Is it possible that sometime between leaving the forest and reaching New York, humans went through a phase of living almost entirely in water? How did they deal with powerful predators like crocodiles? A naked ape in the water would have been extremely vulnerable to such ferocious creatures. (Even today saltwater crocodiles occasionally terrorize villagers living near estuarine swampland in Southeast Asia.) Unlike other mammals, unless we actually learn to swim, we can easily drown when we fall in water; we do not seem to have any instinctive swimming ability. This would be a surprising oversight for an animal with an extended aquatic phase. And why does our skin go all wrinkly when we sit in the bath or swim in the sea? We just don’t appear to be well-enough adapted to be an aquatic species, yet anomalies exist that have not been satisfactorily explained. Why do we have far more sebaceous glands than our nearest primate relatives do? And why do we sweat when most animals pant to reduce body heat? A new explanation is required. All current theories are seriously flawed.

If water was an element in our development, it must have only been a contributory factor. It is just tenable that in the evolutionary history of mankind, there was a period in which water created some adaptive pressure. Along the huge river systems of the Congo and the Amazon, the usual boundary between water and forest is blurred due to seasonal inundation. If water was a factor in establishing bipedalism and hairlessness, it may have been that during the wet seasons water came into the forest, not that mankind’s ancestors left the forest to live aquatically. It is interesting to note that in the Congo gorillas spend time foraging for tasty shoots of water plants. They spend much time in the water but haven’t become hairless. Could this sort of lifestyle really be the reason humans became hairless? It is doubtful.

Vitamin D, however, could be the reason for our hairlessness. This vitamin is important to our health; without it we cannot absorb and assimilate calcium. A deficiency of this vitamin can cause bone disorders like rickets, and a weakness of bones certainly would be a major disadvantage when living even a partially arboreal lifestyle. Vitamin D is unusual as it is in short supply in an exclusively plant-based diet, and our bodies do not absorb it very efficiently from animal products either. But cells in the skin can manufacture it when the skin is exposed to sunlight. A hairy primate gathering fruit in the tops of the canopy would be subjected to enough light to maintain vitamin D production, but a larger primate forced to spend more time on the dark forest floor may have needed to increase the efficiency of the production mechanism. It is possible that hair loss resulted as a response to this pressure, for the sunlight that filtered down to the forest floor would need to be used to the maximum. It is vaguely possible, however, that the continued arboreal lifestyle, with at least some time spent in the upper canopy searching for fruit, could have exposed the top of the head to deleterious effects of direct sunlight. The retention of hair on the scalp could thus provide in these circumstances a positive benefit. This is not a strongly convincing argument, but perhaps it is a little more likely than another suggestion that we have played around with—that head hair provides infants with a convenient handhold on an otherwise slippery parent.

More seriously, there may also be a steroid factor here. Vitamin D is chemically very similar to a steroid. Did the steroid-suppressing chemicals in the fruit inhibit the activity of vitamin D, making the need for a more efficient absorption mechanism all the more vital? Perhaps this extra selection pressure tipped the balance in favor of hairlessness. An imbalance of steroids could also explain the anomaly of our overactive sebaceous glands. We know that if males are castrated the activity of the sebaceous glands (and acne) decreases. So it is possible that today our sebaceous glands are working overtime in response to a heightened internal steroid environment. When we were naked in the forest, our internal steroid activity would have been lower due to the continuous chemical effect of the steroid-suppressing chemicals assimilated via our diet.

Losing hair in the tropical forest environment would not have incurred any major penalties. And while it is extremely unlikely that hairlessness came about as a mechanism for sexual attraction, the sexes may have come to like the look of each other this way. Hair loss may have even had some other advantages, such as enhancing radiant heat loss, though, as other primates in such environment retained their hair, this may have been a minimal or secondary benefit. Naked skin would also increase the efficiency of sweating as a cooling mechanism. Most animals do not sweat anything like as much as humans, but regulate their temperature by panting. The problem with sweating is that it involves a substantial loss of water, but this would not have been a serious disadvantage in the humid forest, particularly for an animal that ate a fruit-and-leaf diet that was composed of 80–90 percent water. But transfer this trait to the savannah, and it does become a serious drawback. Savannah hominids living under the glare of the sun would have to cope with the dangers of dehydration. Certainly sweating as a way of cooling the body, like so many other traits that we regard as uniquely human, could not have evolved in this habitat. All in all, the savannah model is looking increasingly untenable.

It is easy to assume that there was just one lineage that turned into an animal as advanced as a human. Though this may have been the case, it is more likely that there were many branches and many different adaptive solutions to the problems posed by all the various environmental pressures. But in the one particular lineage that happened to survive, all these solutions that we have been discussing came together. There may have been humanlike hominids that were not naked in the forest, and there may have been a humanlike lineage that didn’t develop such efficient bipedalism, but the one lineage that brought all these elements together is the one that survived.

BIG BRAINS

The tropical fruit diet of our ancestors, as we have constantly reiterated, had a marked effect on our anatomical and physiological development. The most significant effect, however, was reserved for our brains. We believe the biochemistry of a fruit diet became the necessary foundation for a chemical drive that turned relatively big-brained primates into great apes and extremely large-brained humans. The chemicals within our ancestor’s fruit diet fueled gradual change and were essential to maintain this change, but what emerged from this was an internal feedback loop that at some point compounded the effect. This second wave of chemical change was an internal mechanism. Maybe neural development in great apes has gone as far as it can without this internal mechanism really taking off. It must be remembered that gorillas, chimpanzees, and humans are genetically extremely close, and of the three, humans are genetically closer to chimpanzees than chimps are to gorillas. Why then are there not three species of African great apes? Why are we so genetically close, yet so different?

As natural selection cannot fully explain the difference, another mechanism must be responsible. We suggest that this internal biochemical mechanism is the crucial missing part of the jigsaw puzzle that propelled humans into a completely different league as far as brain size is concerned. Out of the millions of species that have arisen on this planet, humans display unique traits. Does this not imply there has been a unique process going on? It is encouraging to read that Professor Colin Groves, author of one of the most respected books on primate and human evolution (A Theory of Human and Primate Evolution, 1989), has also suggested that brain growth may not have been selected, as such, but may have happened fortuitously as a result of the changing tempo of our patterns of growth. In a personal communication he confirmed that he still thinks it is likely that human brain expansion occurred as an “epiphenomenon of neoteny.” We will be exploring the details of the fundamental biochemical pathways and biofeedback mechanisms that affected these patterns of growth in the next chapter.

The ideas of Groves are supported by the fact that bonobos possess great latent intelligence. This intelligence arises from their big brains, not vice versa. Bonobos do not use tools in the forest, at least to the extent that chimps do, but when transferred to a different environment, that is, when kept in captivity, bonobos display a greater capacity for tool use (and possess higher levels of cognitive skills) than chimps. In their natural environment, bonobos do not actually need to use tools, as everything they require for survival is readily available. The implication is that bonobos have a greater capability for intelligence than they need, and thus their intelligence is a result of their big brains rather than big brains arising out of the need to develop such things as tool use. As Colin Groves believes, big brains are a by-product of some evolutionary mechanism.

CAST OUT OF THE GARDEN

At some stage humans left the forest. At different phases along the hominid evolutionary way, individuals, groups, and tribes would have left the forest ecosystem to disperse or find new territory. Pressures like climate change and accompanying forest contraction may have also been significant. If they were adapted to eating fruit and the fruit was plentiful, there would be no overt pressure to leave, and, indeed, chimps, bonobos, and gorillas are still there, eating a mainly vegetarian diet. We do know, however, that a cooling climate around a critical time would have resulted in forest shrinkage. Waves of hominid species and even the race that came to be known as Neanderthals may have been forced out of the prime habitat, while the hypothetical lineage that we have been following (and it would have been the best-adapted one) stayed in the forest. But even this lineage left, perhaps somewhere in the region of two hundred thousand years ago. It is accepted that around this crucial juncture, there was a reduction in global temperatures and rainfall, which led to a fragmentation of the forest. If a big central band of forest split, the populations within it would be fragmented, too. If then these smaller forests declined from climactic or even celestial pressures, the populations within would be rendered homeless.

Something evidently forced the whole population out. Perhaps a catastrophic event like a meteor impact tipped the balance. We are now beginning to realize that these catastrophic events were far more numerous than previously thought. In Evolutionary Catastrophes, Vincent Courtillot states, “Over the past 300 million years our planet has been battered by at least seven major ecological catastrophes” (Courtillot 1999). An extraterrestrial impact or violent volcanic activity may have knocked out the fruit-producing capacity of the remaining forest for long enough to have forced an intelligent human to look elsewhere for sustenance.

From mitochondrial DNA analysis we know that at some time in the past our population was extremely small. The billions of humans on our planet are all descended from perhaps as few as five thousand individuals. This suggested bottleneck could have been as a result of an ecological disaster that ravaged population levels, though it is likely that populations in the forest were always small and inbred. Large numbers of humans did not appear until very much later in our history. Bonobo and chimpanzee populations today are relatively small and the breeding rate low, despite the excessive amount of sexual activity particularly displayed by the bonobos. We will be looking at why a predominantly fruit-based diet may have been a contributory factor to this low level of fertility and slow breeding rates later.

Leaving the forest was a highly significant change. The adaptations we have looked at in previous sections (a big brain, an extended juvenile period, a loss of hair, an efficient two-legged gait, and a partial ground-dwelling habit) all stem from the chemical effects of a fruit-based diet. When this drip feed of fruit chemicals was interrupted, some change was inevitable. It would have almost certainly been deleterious, as it would to any creature ousted from its natural habitat. A naked and placid hominid, from an environment in which everything was provided, was suddenly exposed to new and harsh conditions. The biochemistry that its optimal neural function depended on was gone, and it had to fend for itself in extremely different circumstances. But a big brain and intelligent adaptability would have given our ancestors a better chance of meeting the challenges of a different environment. Humans have a physiological adaptability, too; we are able to survive on many different types of diet, ranging from totally plant-based to almost exclusively animal-based diets. But despite this, when the fruit part of the equation was lost, neural and physiological function must have been negatively affected.

Without the biochemistry that was the foundation for our unique development, changes would have been rapid and irreversible. These changes could have even led to the initiation of an unstoppable negative feedback mechanism: even if the forest became habitable again and humans returned to their former way of life, there would have been no guarantee that the brain expansion process would have restarted. During the intervening period, without the forest biochemistry, structural changes would have been initiated; different biochemistry builds different structures, which leads to the emergence of different traits.

We have paid a major price for this change of lifestyle. Although, from the classic survival/competition perspective we are more successful now than we have ever been (and there are some seven billion of us), we suspect that the brains of our close ancestors living in the forest had greater potential than ours do today. We may have slipped away from an opportunity for even greater and possibly more balanced brain development, which would have given us much greater function and a more benign sense of well-being than we possess today.

The forest legacy has left us with a colossal piece of equipment between our ears—give us a problem and we will solve it—but without the foundation of the optimal chemistry provided by a fruit-based diet, we may no longer be able to access our brain’s optimal performance.

AGGRESSION

The classic and rather romanticized image of a placid but physically capable and strong primate-hominid living a carefree life in the forest may not be too far from the truth. It is highly likely that the inherent physiological and psychological state of our ancestors would have been one of underlying ease and contentment. Pumping chemicals from the forest fruits into the hominid system would have limited aggressive behavior. Steroids are linked to aggression, and as we have seen, many of the chemicals found in fruit suppress steroids. They dampen down the effects of testosterone in particular.

The role of androgens, such as testosterone, in precipitating aggressive behavior is clearly displayed in hyenas. In these extraordinary animals females are not only dominant but also highly aggressive; young females regularly kill their siblings. This aggression has been linked to high levels of testosterone. In fact, the females have more testosterone than the males and even possess pseudomale genitalia.

Internal steroid activity would have been altered when humans left the forest and fruit was lost as the major part of the diet. Not only would steroid suppression have been lifted, but eating different foods instead would have made matters even worse. Meat contains steroids, thus a change to a carnivorous diet would have caused a major biochemical upset; not only would the steroid-suppressing elements in the diet have been lost, but extra steroids also would be taken in. Research has found that eating animal fats increases levels of testosterone: “double whammy” is the current phrase that springs to mind.

It is sobering to note that humans killed in excess of one hundred million fellow humans in the twentieth century alone. Today we live surrounded by mental, emotional, and physical torture. There is cruelty to others and to the animals we live with, and we are rapidly destroying the planet that sustains us. Is it possible that this sickness (and it really is a sickness) stems from an imbalance in our biochemistry initiated by the loss of steroid suppression all those years ago? Without doubt, something has gone wrong. In his famous book The Ghost in the Machine, Arthur Koestler drew similar conclusions.

When one contemplates the streak of insanity running through human history, it appears that Homo sapiens is a biological freak, the result of some remarkable mistake in the evolutionary process. The ancient doctrine of original sin, variants of which occur independently in the mythologies of diverse cultures, could be a reflection of man’s awareness of his own inadequacy, of the intuitive hunch that somewhere along the line of his ascent something has gone wrong.

To put it vulgarly, we are led to suspect that there is somewhere a screw loose in the human mind. We ought to give serious consideration that somewhere along the line something has gone seriously wrong with the evolution of the nervous system of Homo sapiens. We know that evolution can lead into a blind alley, and we also know that the evolution of the human brain was an unprecedentedly rapid, almost explosive, process. Let us note as a possible hypothesis that the delusional streak which runs through our history may be an endemic form of paranoia, built into the wiring circuits of the human brain. (Koestler 1968, 267, p. 239)

Would it not be wonderful to identify the mechanism of our insanity, for then we could do something about it? Real healing and restoration of a balanced consciousness may be realistic, but initially we need to recognize the depths and significance of the problem.

WHY DID OUR BRAINS STOP EXPANDING?

In the forest the human brain was expanding and expanding at a phenomenal rate. Sometime at around 200,000 to 150,000 years ago, this process came to an end. The brain stopped expanding and started to shrink. This key point in our evolutionary journey has been noted but rarely addressed, and its significance comprehensively ignored.

Christopher Ruff, of John Hopkins University, and his colleagues thoroughly analyzed the fossil record to determine the evolving body mass and brain size of the various Homo species leading up to us. The results show that the assumption of a straight progression from a pea-brained ancestor to the ultrabrainy modern Homo sapiens is decidedly shaky. Hominid brains appear to have remained fairly constant in size for a long period from some 1.8 million years ago until about 600,000 years ago. But then, from 600,000 to 150,000 years before the present, fossils show that the cranial capacity of our ancestors skyrocketed. Brain mass peaked at about 1,440 grams (3.17 pounds). Since then brain mass has declined to the 1,300 grams (2.87 pounds) that is typical today (Ruff 1997).

Of course, brain size alone does not tell the whole story. Brain size also correlates with body size, and the peak of brain size roughly corresponds to the peak in archaic Homo sapiens’ body size (the Neanderthals). The decline in size of the body in Homo sapiens sapiens (modern humans get two “wises” in our name, but do we really deserve it?) over the past fifty thousand years has raised our ratio of brain-to-body size to just above Neanderthal levels. Yet we have done this by shrinking our bodies to a greater extent than our brains have shrunk. There is some evidence that our brains are still shrinking and that they may have done so over the last ten thousand years by as much as 5 percent.

This very recent period of brain shrinkage coincides with a major dietary change, for it was around this period that cereals and grain (grass seed) came to the fore. Cereals and grains may be the foundation of our diet today and responsible for the huge explosion in our numbers, but they may not be the best foods for optimal function. Indeed, studies of skeletons from early agricultural societies show that ill health accompanies the initial transition to eating more grains and cereals. Skeletons dug up from the East Coast of the United States, dating from around 1000 CE, the era when Native Americans switched to corn-based agriculture, are smaller than earlier skeletons. Studies of skeletons from other societies undergoing this transition show signs of deficiencies such as anemia. Clark Larsen, the physical anthropologist who studied the East Coast skeletons, has stated, “Just about anywhere that this transition to cereals occurs, health declines”(Larsen 2002).

It is thought that humans from such agrarian societies were lucky to live beyond thirty years. In contrast forest apes, such as chimpanzees, can live for some sixty years. We can reasonably assume that humans in the forest lived easily as long if not longer. Furthermore, if man in the forest was as long-lived or even longer-lived than chimps, it would provide a strong argument for the notion that this was both the most natural and most suitable place, particularly in terms of diet, for a human to live.

ANCESTRAL DIETS

If the evolution of the unique human system was somehow linked with our ancestral diet, we would expect the human system still to be best adapted to something approaching this. While there is continued debate on this subject, few dissent from the view that there is an increasing problem with the food we are eating in our sophisticated, time-stressed modern world. In just one six-week period, newspaper headlines in the United Kingdom announced: “World Alert over Cancer Chemical in Cooked Food” (Daily Telegraph, May 18, 2002); “Children at Risk from the Junk Food Time Bomb” (Daily Mail, May 31, 2002); and “Anti-social Conduct May Be Linked to Diet, Says Study” (Guardian, June 26, 2002). This is a small sample of worries arising from recent research. Today, we are told we risk diabetes, heart disease, and cancers from eating the “wrong sort of food.” Weight problems caused by an addiction to high-fat and high-sugar convenience foods, or simply an ignorance of the alternatives, carry the risk of these and other diseases manifesting in later life. One in ten children under age four is now classified as obese, and health problems resulting from being overweight cost Britain some two billion pounds a year. It has been estimated that if we continue eating a “junk food” diet, in forty years time half the population will be obese. Furthermore, specialists also fear that anemia due to poor nutrition in early life can have long-lasting effects on a child’s mental development and learning ability.

Although longevity has increased over the last few centuries, many folk live the last years of their lives with the fear of disease, if not the actuality of it, but old age and disease do not necessarily go together. In the remote Andean highlands of Ecuador, there are communities of people who it is claimed live for 140 years or more and who remain agile and lucid right to the end. Death from heart disease and cancer is unknown in these high mountain valleys but rife in nearby towns. David Davies, an English zoologist and member of the gerontology clinic, University College, London, who has made a study of these “centenarians of the Andes,” found that the people who have the best chance of a healthy old age are those who actively use their minds and bodies, even toward the end of their life span. He looked at many elements of their life and environment, from genetic factors to the tranquility and lack of stress in their way of life. The folk who lived longest were found among those who lived on a subsistence diet, which was low in calories and animal fat. Typically, the main meal of the day was eaten in the early evening and was made up of very small wild potatoes, yukka, cottage cheese, and maize or bean gruel. Melons were eaten for dessert. Sometimes green vegetables, cabbage, or pumpkins were added to the menu, and sweet corn cobs were often taken to work for lunch. The people working in the fields ate fruit throughout the day. The climate is ideal for citrus fruits, and many other “hedgerow” fruits such as mora (like a blackberry), guava, and naranjilla are abundant, too. Meat was only eaten rarely, a type of cottage cheese was made from goat or cow milk, and eggs were eaten raw or almost raw (Davies 1975).

Though these people are very healthy and extremely long-lived, we mustn’t necessarily jump to the conclusion that this diet is perfect for the human system; their diet is restricted by the environment they live in. However, if we look at other communities of long-lived folk, the parallels are striking. The Hunzas of northeast Kashmir also live in mountainous regions and have a diet that includes wheat, barley, buckwheat, beans, chickpeas, lentils, sprouted pulses, pumpkins, cottage cheese, and fruit—the famous Hunza apricots and wild mulberries. Meat is again only eaten rarely, and because fuel is in short supply, when food is cooked it is usually steamed—a method of cooking that is the least damaging to the chemical nutrients in the food. Hunzukut males, like the people in the Andean highlands, are also reported to live to 140 years of age. So, we must conclude that these diets are, at the very least, much more suitable than the ones we depend on in the affluent industrialized countries.

There seems to be no definitive study that has so far convinced society as a whole that nutritionally we are barking up the wrong tree (or at least not picking from the right one). But there are many scraps of information that support the thesis that a more natural diet is the most beneficial option. Lymphocyte production and hence resistance to illness is boosted by consuming the nutrients that occur in optimal proportions and quantities in uncooked vegetables. There are also a huge number of cases in which raw food, particularly fruit and vegetable juices, has seemingly cured a wide range of illnesses. Migraines, skin complaints, tuberculosis, mental disorders, heart disease, cancers, and a host of other diseases have responded favorably to a diet rich in raw food. There are clinics, foundations, and institutions throughout the world that offer therapies based on “living nutrition.” Such diets are much closer to our ancestral diets than the chips, pies, and cookies that adorn most of our supermarket shelves.

As with all organisms, hominids in the course of evolution were locked into the biological matrix of their environment. Whether our diet consisted of insects, fruit, or meat, it was all biologically active material. Some primates today eat a bit more of this or that; much coverage has been given recently to meat-eating chimps, but this comprises a relatively small percentage of their diet. Despite their skill in capturing live prey, chimpanzees actually obtain about 94 percent of their annual diet from plants, primarily ripe fruits. Primate biochemistry is largely based on plants, and a plant-based diet is what hominids were eating during their evolutionary development. A pictorial representation of an early human living in the forest, lounging around eating fruit, may be more accurate than one in which he is dressed in animal skins, spear in hand, on the hostile open plains.

The lack of plant material in the fossil record has led, according to Richard Leakey, the paleoanthropologist famed for his work in Kenya, to an overemphasis on meat eating as a component of the early hominids’ life. He also finds some of the work on tooth analysis “very surprising” (Leakey, 1981, 74). The teeth of Australopithecus robustus fall into the fruit-eating category. The patterns of wear and the small scratches left on the enamel appear very similar to those of the forest-dwelling chimpanzees, yet here was a hominid that was supposed to live on the plains in an era when the climate was dry and the vegetation mainly grass. The examples of Ramapithecus teeth that have been similarly analyzed show exactly the same patterns, and the teeth of Homo habilis, the first creature to be awarded Homo status, also have smooth enamel typical of a chimpanzee. This evidence is extremely relevant. All the early hominids and their great ape cousins were mainly fruit-eaters. The teeth of Homo erectus suggest a more omnivorous diet. The enamel from their teeth shows scratches and scars that are compatible with grit damage, possibly from consuming bulbs and tubers. As a response to a cooling climate and a contraction of the forest, did this species widen its diet to adapt to a new environment? Some forest would have remained intact along the wetter river systems. Chimpanzees and gorillas survived there along with, we suspect, another hominid whose teeth were very well adapted to fruit eating—Homo sapiens.

Primates, given a choice, will select fruit in preference to any other food. Fruit is a rich, nutritious, and easily digestible food. If it is available, this is what all the great apes prefer to eat. However, other foods are eaten regularly. Our nearest relative, the bonobo, eats between 60 percent and 95 percent fruit, depending on the fruit productivity of its specific habitat. The rest of its diet comprises mostly shoots and herbs and a small amount of insects, eggs, and the occasional small mammal. Fallback foods like bark may also be eaten in times of fruit scarcity.

What humans in the forest ate is, of course, unknown, but it is likely that they would have eaten a similar balance of foodstuffs. They would not have been purely vegetarians. Even figs (perhaps the most preferred food) contain a small amount of insect matter as their pollination mechanism results in eggs and larvae of small wasp species remaining in the fruit. These insects may have served as an important source of essential micronutrients such as vitamin B12 and provided a little extra protein.

As they were the most highly intelligent animals in the forest and fruit was the best food, it is likely that humans developed strategies to maintain a high percentage of fruit all year round. Being efficient bipeds would have given them the potential to travel easily between widely separated fruit sources. The quest for distant fruit trees may have even honed their bipedal adaptation. The larger arboreal primates are known to travel on the ground between distant fruit trees, as it is more efficient than traveling in the trees. Archaic humans, being better-adapted bipeds than apes, would have found this way of life much easier.

HUMANS ARE BY NATURE FRUGIVOROUS

There has been much study and even more speculation about what sort of diet our teeth and guts are best designed for. From the type of dentition, gut length, and toxicity of foods like meat, a very strong case can be built for Homo sapiens being designed to eat and process a largely fruit-based diet. The brain’s requirements for food and the gut’s requirements for energy, the optimal acid/alkali balance, and the structure of the intestines all point to a frugivorous diet. A shift to fruit specialization answers all the problems and anomalies that have spawned countless conflicting theories.

Katherine Milton, professor of anthropology at the University of California, Berkeley, has carried out important work on diet and primate evolution. Her research has led her to believe that “the strategies early primates adopted to cope with the dietary challenges of the arboreal environment profoundly influenced their evolutionary trajectory” (Milton 1993). This has a great significance for us today for the foods eaten by humans now bear little resemblance to the plant-based diets anthropoids have favored since their emergence. She believes these findings shed light on many of the health problems that are common, especially in our industrially advanced nations. Could they be, at least in part, due to a mismatch between the diets we now eat and those to which our bodies became adapted over millions of years?

The plant-based food available in the forest canopy comprises fruit and leaves, but subsisting on this diet poses some challenges for any animal living there. For a start it is high in fiber that is not only difficult to break down and hence digest but also takes up space in the gut that may otherwise be filled with more nutritious foods. Many plant foods also lack one or more essential nutrients such as amino acids, so animals that depend on plants for meeting their daily nutritional requirements must seek out a variety of complementary food sources. Fruit is usually the food of preference, for it is rich in easily digested forms of carbohydrate and relatively low in fiber, but its protein content is low (the seeds may be protein rich, however). Leaves offer higher protein content, but they are lower in nutrients and contain much more fiber. Balancing these constraints has led to different strategies that are reflected in behavior and physiology. Colobine monkeys have compartmentalized stomachs (a system analogous to that of ruminants) that allow fiber to be fermented and hence processed very efficiently, but humans and most other primates pass fiber largely unchanged through their digestive systems. Some fiber can be broken down in the hind gut of these latter species, but the process is not as efficient as that in the Colobus genus.

Milton’s research focused on two contrasting species of South American primates: howler and spider monkeys. These two species are about the same size and weight as each other and live in the same environment, eating plant-based foods, yet they are very different. Howler monkeys have a large colon, and food passes through their digestive system slowly, whereas spider monkeys have a small colon through which food passes more quickly. These physiological differences relate to dietary specialization. The foundation of the howlers’ diet is young leaves: 48 percent of their diet is leaves, with 42 percent fruit and 10 percent flowers. The spider monkeys’ diet comprises 72 percent fruit, 22 percent leaves, and 6 percent flowers. Another fundamental difference is that although these animals are the same size, the brains of spider monkeys are twice the size of howler brains. Very significantly, Milton comments, “The spider monkeys in Panama seemed ‘smarter’ than the howlers—almost human” (Milton 1993).

This is something we have commented on before: big brains and a diet high in fruit appear to go together. Why should this be so? Could this brain enlargement result from the need to memorize the location of productive fruit trees, as some have suggested, or did elements within the fruit itself fuel this change more directly, as we propose? Animals such as squirrels, and even birds like jays, memorize the locations of stored food most efficiently without an overlarge brain, thus it seems that something else must be responsible.

Although Milton has concluded that it is quite difficult for primates to obtain adequate nutrition in the canopy, she observed that spider monkeys consume ripe fruits for most of the year, eating only a small amount of leaves. Bonobos also appear to find enough food to eat easily, for much of their time is spent in other “social” activities. Thus being a fruit-eating forest primate appears a very viable option, but one question remains: If fruit is so low in protein, how do these fruit specialists obtain an adequate supply of these essential nutrients? Milton found that spider monkeys pass food through their colons more quickly than leaf-eaters such as howler monkeys. This speed of transit means that spider monkeys have a less efficient extraction process, but as much more food can be processed, it more than makes up. By choosing fruits that are highly digestible and rich in energy, they attain all the calories they need and some of the protein. They then supplement their basic fruit-pulp diet with a very few select young leaves that supply the rest of the protein they require, without an excess of fiber. Of course, by processing so much fruit, a large quantity of chemicals that naturally occur in fruit will also be absorbed. It should also be noted that wild fruit contains a higher percentage of protein than the cultivated fruit that is available to us humans today. It is clear that many wild primates are able to satisfy their daily protein and energy requirements on a diet largely or entirely derived from plants. It is likely that our ancestors in the forest did, too.

As stated, the wild fruit that we propose was the mainstay of our ancestral diet for the longest and most significant part of our evolutionary history contains more fiber than the fruit we buy today in our shops. Chimpanzees take in about 100 grams (3.52 ounces) of fiber a day compared with about 10 grams (0.35 ounces) that the average Western human consumes. At one time it was believed that humans did not possess microbes capable of breaking down fiber. Studies on the digestion of fiber by twenty-four male college students at Cornell University, however, found that bacteria in their colons proved quite efficient at fermenting the fiber of fruit and vegetables. The microbial populations fermented some three-quarters of the cell wall material, and about 90 percent of the volatile fatty acids that resulted were delivered to the bloodstream (Wrick et al 1983). It has been estimated that some present-day human populations with a high intake of dietary fiber may derive 10 percent or more of their required daily energy from volatile fatty acids produced in fermentation.

Furthermore, experimental work on human fiber digestion has shown that our gut microfloras are very sensitive to different types of dietary fiber. We are very efficient at processing vegetable fiber from dicotyledonous sources (flowering plants like fig trees, carrots, and lettuces) but are less so from monocotyledons (grasses and cereals). This provides yet another pointer to the archaic diet of humans as being largely fruit based and indicates that the grass seed that we eat so much of today in cereals, cookies, and much else is a poor substitute.

The chimpanzee gut is strikingly similar to the human gut in the way it processes fiber. As the percentage of fiber in the diet increases, both humans and chimpanzees increase the rate at which they pass food through the gut. These similarities indicate that when food quality declines both these primates are evolutionarily programmed to respond to this decrease by increasing the rate at which food passes through the digestive tract. And this compensates for the reduced quality of the food available.

It appears that the human system then, like those of the chimps and bonobos, is designed for a plant-rich fibrous diet. We are not designed for a diet high in refined carbohydrates and low in fiber or one that includes significant quantities of animal protein. Meat eating in man has been, on an evolutionary timescale, a very recent development. It certainly couldn’t have influenced the development of our physiology. Though the passage of food through the guts of spider monkeys, chimps, and humans is faster than in leaf specialists like howlers, it is much slower than in carnivores. Meat hanging around in the digestive system is bad news because of its inherent toxicity. The transit time for the passage of food through a carnivore’s gut is between seven and twenty-six hours, while for humans it is between forty and sixty hours.

Though we do have a shorter colon and a longer small intestine than the great apes (and this has led one camp of researchers to speculate that our intestines are more similar to those of carnivores), these differences are more appropriately explained by a specialist fruit diet, not a carnivorous or grain-based one. Fruit is easier to digest than leaves, tubers, and stems, and has a lower fiber content. Thus a specialist fruit-eater would not need such a long colon as other apes that have more fibrous bulk to deal with.

Another feature of humans that is strongly indicative of our vegetarian origins is our inability to synthesize our own internal vitamin C. This trait is very rare, but where it occurs, the animals concerned (such as guinea pigs) eat a plant-based diet. In these cases ample supplies of the vitamin are available within the food. Vitamin C plays many extremely important roles within the human body. Research seems to be always finding more functions for this “miracle chemical.” These have been summarized by Ross Pelton, clinical nutritionist and cancer researcher at the University of California, in his book Mind Foods and Smart Pills: Vitamin C stimulates the immune system, enabling one to better resist diseases. Terminal cancer patients taking megadoses of vitamin C have been found to live longer. It promotes faster wound healing and reduces the amount of cholesterol in the blood. It is a powerful detoxifier and protects against the destructive power of many pollutants. In addition, it protects the body against heart disease, reduces anxiety, and is a natural antihistamine. A severe deficiency causes scurvy and eventually death. Increasing its intake has been found to increase mental alertness and brain functioning in a variety of ways. Vitamin C is the main antioxidant that circulates in the blood. When available in sufficient quantity, blood carries it around the body, washing over the cells to create a bath of protection. Whenever a free radical turns up, a molecule of vitamin C gives up one of its own electrons to render the free radical ineffective. According to Pelton this process may take place somewhere between one hundred thousand and one million times a second, depending on the body’s level of metabolism and the amount of vitamin C available. Unfortunately, with each free radical decimated, a molecule of vitamin C is lost, so the body rapidly loses its supply of vitamin C (Pelton 1989).

Vitamin C is a key player in keeping our neural system healthy. The body has a system that operates like a kind of a pump to concentrate vitamin C around our nerve and brain tissues. These tissues have more unsaturated fats than any other organs in the body, making them more vulnerable to attack by free radicals and oxidation. The vitamin C pump removes vitamin C from the blood as it circulates to increase the amount of vitamin C in the cerebrospinal fluid by a factor of ten. The pump then takes the concentrated vitamin C from the cerebrospinal fluid and concentrates it tenfold again in the nerve cells around the brain and spinal cord. Thus our brain and spinal cord cells are protected against free radical damage by more than a hundred times as much vitamin C as our other body cells.

For such an important chemical, it is extremely odd that we are dependent on vitamin C from outside sources. But how much of it does the body need? Research carried out by the Committee on Animal Nutrition demonstrated that monkeys needed around 55 milligrams of vitamin C per kilogram (2.2 pounds) of body weight. When this measure is extrapolated to humans, a 150-pound person would need a daily intake of 3,850 milligrams. Nutritional science recommends that a human needs 45 milligrams each day. This is just enough to prevent scurvy but not enough to keep the body functioning at an optimal level. We would not, and indeed do not, obtain the sort of levels our bodies really need from a diet high in meat and low in vegetables and fruit, but we would from one high in fruit, shoots, and leaves. Analysis of wild plant foods eaten by primates shows that many of these foods contain notable amounts of vitamin C. The young leaves and unripe fruit of one species of wild fig were found to contain some of the highest levels ever reported. Our closest living relatives, the great apes, eat a diet that contains between 2 and 6 grams (0.07 to 0.21 ounces) of vitamin C every day. When our ancestors were living in the forest they would have consumed similar amounts.

In contrast, we can and do produce our own vitamin D. This vitamin cannot be obtained from a leaf- and fruit-based diet, but it can from a carnivorous one, thus if we were designed to eat meat we would have less need to synthesize our own. Being able to synthesize vitamin D and not vitamin C is then a strong indication of our true ancestral diet and the one we are really adapted to. Accumulating evidence for meat being an unhealthy food option further strengthens this case. One study at the Cancer Epidemiology Unit in Oxford showed that vegetarians were 24 percent less likely than nonvegetarians to die of ischemic heart disease (Key 1999).

Carbohydrates also appear to be problematical when eaten in large amounts. A diet high in carbohydrates, especially refined carbohydrates (cakes, cookies, pasta, etc.), dumps large amounts of glucose rapidly into our bloodstream. This can cause insulin resistance in which the absorption of glucose from the bloodstream is disrupted. This in turn can lead to obesity, adult onset diabetes, hypertension, heart attacks, and strokes. It can also lead to an excess of male hormones, which, among other effects (e.g., aggression), encourages pores in the skin to ooze large amounts of sebum. Acne-promoting bacteria thrive on sebum. Up to 60 percent of twelve-year-olds and 95 percent of eighteen-year-olds in modern society suffer from acne, yet it is almost unknown in subsistence societies such as the Kitava Islanders in Papua, New Guinea, and the Ache of the Amazon. The Inuit people of Alaska also used to be free of acne, but they began to be affected by these skin complaints after they started to eat processed foods.

The problem with eating highly processed carbohydrates may be further reaching still. If refined cereal consumption results in an excess of male hormones it could have a ripple effect on the immune system for we know that the thymus gland starts to shrink in response to these hormones at the time of puberty. (More carbohydrates lead to more testosterone, which shrinks the thymus gland, which is seat of much of our immune response.) Grain products have also been associated with celiac disease, an autoimmune condition of the gut, and some researchers suspect they trigger rheumatoid arthritis, too.

It is highly significant that these foods have the ability to alter the quantity or at least the activity of our hormones. It is another example of the way our diet can affect the way our bodies work. It is possible, probable even, that they also affect the way we act, and thus how we moderate our sense of self. If we compare refined carbohydrates with fruit, we can see that fruit has a much lower glycemic index, which means it is digested more slowly, thus avoiding the problems of the “glucose rush.” The chemicals within fruit also reduce the activity of sex hormones. They thus have the diametrically opposite effect to that of refined cereals.

There is a view held by some that meat, and particularly the high protein content of meat, was somehow responsible for the enlargement of our brains. The assumed “higher-quality” meat diet theoretically allowed more energy to fuel the brain with a shorter small intestine. This reasoning is flawed on several fronts. First, meat is supposed to be easy to digest and to be a high-energy food, but fruit is much more easily digested and provides more readily available energy, too. Second, if there were sufficient external pressure to bring about such a change as a shortening of the gut, we would expect other adaptations and changes toward a carnivorous diet as well. Certainly we would not expect adaptations to be heading in the opposite direction. Our teeth, for instance, are nothing like the teeth of a carnivore. The teeth of our nearest relative, the bonobo, are much better adapted to eating meat than human teeth are, and bonobos hardly eat any meat. In fact, it is known that bonobos are, if anything, more intelligent than chimpanzees, and it is chimps that eat at least some meat. So, if bringing meat into the diet of an ancestral human was enough to shorten the gut and expand the brain (both major changes), where are the parallel changes in areas that would be needed to cope with a meat diet?

If we look at areas such as dentition, the physiology to digest meat, and the ability to catch it, we find nothing that looks even vaguely carnivorous. If we lined up the three most evolved species of primates— chimps, bonobos, and humans—we would have to conclude that humans are, in fact, the least adapted to eat meat. Humans have much smaller teeth, and they cannot chase the meat nearly so well. Also there is a structural distinction between carnivore guts and those of frugivores or vegetarians. Our guts are like those of the noncarnivores; they are folded, smooth, and still significantly longer than a carnivore gut. There is a difference in saliva as well. Carnivore saliva is acidic, but the saliva of humans is alkaline, which provides the right functional environment for digestive enzymes, such as amylase, to break down starch.

Now, if we ask what sort of food really fits these human adaptations, we have to conclude it is fruit. Fruit fits the brain-gut energy equation: the shorter gut, the more ease of digestion, the lower the toxicity, and the smaller the teeth. Fruit is easy to assimilate, and the nutrition it provides is in a form that needs very little conversion to the real requirement of the brain—glucose. (The sugar in wild fruit tends to be rich in glucose and fructose compared with cultivated fruit that has been bred for its sweeter-tasting sucrose content.) Humans thus have a proportionately shorter small intestine than chimps and bonobos, not because of increased levels of meat in our diet but because of an increased specialization on sugar-rich fruit. High-quality fruit is low in toxicity and provides all the fuel the brain needs. Meat, conversely, is more difficult to digest, particularly without cooking, and then to turn protein into sugar requires yet more energy. So meat as an energy food doesn’t make as much sense as fruit that is full of fruit sugars that are easily assimilated and take little conversion.

The anatomy and physiology of our digestive system support the case for the biochemical role of tropical fruit in human development. However, the case could be stronger still if we could show that the human brain in archaic times actually worked the digestive system in a way that extracted the nutritive elements within the plant-based diets more efficiently. More research needs to be done in this area, but preliminary indications (from T. W.’s private research) hint that a digestive system run without interference from the left hemisphere may do just that.

PROTEIN, FATTY ACIDS, AND WATER

We need to look at the whole matter of protein requirement in a little more depth. Perhaps we do not need as much as is widely assumed. The time of our life when we need the richest and highest quality nutrients is in our first few years of life, when our bodies and brain tissues are growing most rapidly. It is surprising then to discover that human breast milk has a protein content of less than 10 percent. Breast milk is sweet and rich in fat, providing sugar to physiologically fuel the baby and fat to build it. It is a low-protein food.

Research has illuminated the vital necessity of adequate polyunsaturated fats for brain development, particularly in forming nerve fiber membranes. But in their first four months, babies do not produce the enzymes needed to make certain long-chain fatty acids. The only source of these acids is the milk they consume. The food mothers eat during their breast-feeding stage has been found to affect the balance of fats in their infants. In one study the baby of a mother who ate a diet that excluded all animal products had twice as much polyunsaturated fat in its adipose tissue than did babies whose mothers were omnivorous. The conclusion was that babies breast-fed by mothers who eat an exclusively plant-based diet have better brain development because of the role of polyunsaturates in the growth of neural membranes. This study again points to the suitability of a fruit-based diet and its link to neural development (Spinney 1995).

In the first year of life, no less than 60 percent of a baby’s energy intake fuels brain growth. Referring back to Katherine Milton’s spider monkey study, we could ask whether they were really eating leaves for their protein content. They may have been primarily after additional essential polyunsaturated fats.

Fatty acids play an essential role in the structure and function of the brain. (Two of them alone, arachidonic acid and docosahexenoic acid, constitute 20 percent of the dry weight of the brain.) These are biologically highly active compounds that perform numerous regulatory functions in the brain and the rest of the body. Many of them can be synthesized by the body if the diet provides enough of the raw materials for construction, but some, such as linoleic (omega 6) acid and alpha-linolenic (omega 3) acid, are only available from the food we eat, they are thus termed “essential fatty acids.”

Wild foods routinely eaten by monkeys contain notable amounts of alpha-linolenic and linoleic acids. The diet of our human ancestors would have been similarly rich in these essential fatty acids. In fact, analysis of wild plant foods eaten by free-ranging primates shows that these foods are generally high in the nutrients we know are necessary for human health. Natural primate diets contain a greater proportion of many minerals, vitamins, and essential fatty acids as well as dietary fiber than does the diet of modern humans. It is likely, then, that the present recommended daily requirements for these dietary components are set far too low.

Animal studies have also shown that neural integrity and function can be permanently disrupted by deficits of fatty acids during fetal and neonatal development. These nutrients are extremely important. Research has indicated that infants may benefit markedly from the long-chain polyunsaturated fatty acids naturally present in breast milk. It is highly likely that most of us are chronically short of these nutrients as they are in short supply in our modern diet and, even more crucially, are absent from many baby formula foods.

Considerable evidence is now accumulating that indicates that deficiencies in essential fatty acids are a major contributory factor in a range of interrelated childhood disorders, including attention deficit and hyperactivity disorder, dyslexia, asthma, allergies, and even autism. It has also been shown that correcting these deficiencies can significantly improve health.

Appleton Central Alternative Charter High School in Wisconsin caters to students with behavioral and learning difficulties. In 2003 they instigated a well-being and health food program. The junk food vending machines were removed, and proper lunches were offered that included raw vegetables, fresh fruit, and whole grain breads. School staff members assert that students’ disruptive behaviors and health complaints diminished substantially. Students also seemed more able to concentrate. They also became more stable, so their mental health and anger management issues were easier to manage. Teacher Mary Bruyette said she saw changes “overnight.” She noticed a considerable decrease in impulsive behaviors such as talking out, fidgeting, and the use of foul language. Henceforth she has had fewer disciplinary referrals to the office for students who could not settle down and do their coursework. Complaints of headaches, stomachaches, and feeling tired also lessened. Students were no longer hungry midmorning or midafternoon. According to Principal LuAnn Coenen, negative behaviors such as vandalism, drug and weapons violations, dropout and expulsion rates, and suicide attempts are now virtually nonexistent (Keeley 2004).

The school also experimented with junk food days when the students reverted to a diet of chips, brownies, candy bars, and sugared sodas. Students became tense and “wired.” They were unable to focus and complained of stomachaches and tiredness. Students and staff members mutually agreed to abandon such days. The negative effects of such junk food have been further highlighted in the shocking 2004 film Super Size Me.

Just replacing sodas with water can make a significant difference. Most humans today are chronically dehydrated. This simple fact causes much ill health. According to Dr. F. Batmanghelidj, in his book Your Body’s Many Cries for Water, many of the degenerative diseases of the human body are caused by a simple lack of water. He has concluded from his studies that asthma, diabetes, arthritis, angina, obesity, Alzheimer’s disease, high cholesterol, hypertension, dyspeptic pain, and many other maladies are signals from a body that is desperately thirsty (Batmanghelidj 2000). We are much more prone to dehydration if the bulk of the food we live on is dry. Fruits and vegetables have a much higher water content than grain- and wheat-based products. That our bodies work more efficiently when we live on the diet that provides not only the nutrients that we need but also basics like our water is further evidence for this diet being the one we have been “designed” for.

SUMMARY

In this chapter we have presented the framework for an alternative mechanism that we think was fundamental to the evolution of humans, hominids, and perhaps to the great apes. We have argued that humans are best adapted to a diet high in fruit and that this diet played a significant role in our development. Primates evolved a unique biochemistry based on their environment. This environment may have been stable for millions of years, and over such long stretches of time, this rich chemical matrix would have had a very real effect. If in the distant past, humans and protohumans ate a diet consisting mainly of fruit, then the chemicals contained within the fruit would have flowed through their bodies for countless generations. This biochemical influence could have caused, for instance, a lengthening of the juvenile period and much else besides. In the next chapter we will look in detail at these biochemical pathways and how they acted on the human system.