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Brain size shrinking

Why did our brains stop expanding?

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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.

Human brain shrinking fast

The human brain is shrinking faster than the shrinkage of the body. Image credit:

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.

The food of the Hunzas

The food of the Hunzas. Photo source.

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.

Hominids eating fruits and vegetables

Research shows early hominids ate mostly fruit and vegetables. Image source.

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 B 12 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.


Davies, David.  Centenarians of the Andes. Norwell, Mass.: Anchor Press, 1975.

Larsen, Spencer.  Skeletons in Our Closet: Revealing Our Past through Bioarchaeology. Princeton: Princeton University Press, 2002.

Leakey, Richard.  The Making of Mankind. London: Michael Joseph Limited, 1981.

Ruff, C. B., E. Trinkaus, and T. W. Holliday. “Body Mass and Encephalization in Pleistocene Homo.” Nature 387 (1997): 173–76.

The article is excerpted from Return to the Brain of Eden: Restoring the Connection between Neurochemistry and Consciousness by Tony Wright and Graham Gynn, recently published by Inner Traditions.

Submitted by Trevor Smith



ledom's picture

Our brains stopped expanding because women couldn’t give birth to babies with larger heads.

To anyone interested in the diets of traditional/non-modernized people please look into the works of Weston A Price. The book Nutrition And Physical Degeneration presents great evidence of the superior health of those following their ancient traditional lifestyles and foods. Dr. Price found that when those same types of people were exposed to modern processed foods they would become very sick and experience the same health problems we know today such as tooth decay, heart problems, TB, infertility ext. The traditional diets varied from group to group, but they all had some important things in common. They all ate some meat or fish, and always preferred the organ meat and fat to the muscle meat. Those that ate only a little meat or fish ate plenty of grass fed raw cultured dairy instead. Grains were consumed far less than in our modern culture, and when they were consumed they were prepared very carefully with soaking, sprouting and often fermenting. One of the other main similarities was the absence or rarity of refined sugars. These people lived on highly nutritious foods, grown or raised wild or grown on fertile mineral rich soil. One thing both the Hunza and andian regions have in common along with high altitude is very mineral rich soil and water, thus naturally more nutrient dense foods.

If you take the time to read the sources, it answer your argument about rural area quite well.

« The scientists found that the residents of Vilcabamba, who were principally of European descent, had very low cholesterol levels and very few of them ever suffered from heart disease. But more remarkable was the longevity of the Vilcabambans. Many of the town residents claimed to be over 100 years old. A few of them stated their age as being over 140 years old. These ages appeared to be confirmed by birth and baptismal records. »

But, by the end of the research there is a nice turn over

«Recognizing the importance of establishing the accurate age of the villagers, Leaf persuaded Dr. Richard Mazess of the University of Wisconsin Madison and Dr. Sylvia Forman of the University of California Berkeley to help uncover the accurate ages of Vilcabamba's elderly population.

What they found shocked them. In reality, there was not a single centenarian living in Vilcabamba. The oldest person in the village was 96. The average age of those claiming to be over 100 years was actually 86 years. The researchers presented these results on February 27, 1978 at a workshop at the National Institutes of Health in Bethesda, Md.»

And then why the batismal record was not read correctly at first :

«The second source of error was the widespread use of identical names in the small, rather inbred community. This had initially confused researchers who had studied the baptismal and birth records. The birth-date of an identically named uncle or father would appear to confirm the extreme longevity of a resident. By asking the Vilcabambans for the names of their godparents, the researchers were able to identify the correct records for each resident.»


Ever notice that every single report of a human being living past 120 comes from a primitive rural part of the world where the birth certificate system is nonexistent or unreliable? Either it's their rural existence and their diet, or the reports are simply untrue. I vote for the latter. Call me an ignorant Bible thumper if you want, but I think Genesis 6:3, "And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years," has put an absolute limit on our longevity... just one of the clues to the Truth.

Ever notice that every single report of a human being living past 120 comes from a primitive rural part of the world where the birth certificate system is nonexistent or unreliable? Either it's their rural existence and their diet, or the reports are simply untrue. I vote for the latter. Call me an ignorant Bible thumper if you want, but I think Genesis 6:3, "And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years," has put an absolute limit on our longevity... just one of the clues to the Truth.


trevorsmith's picture

Trevor Smith

Trevor Smith

Trevor Smith studies cognitive science in the US and has been heavily interested in the relationship between different states of consciousness and the configuration of our neural arc hitecture; focusing on yoga, meditation, shamanism and science as his... Read More

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