7. The Evolution of Hominids

7.8 The biochemical basis of hominisation

For a long time, the paradigm of protein synthesis was: “one gene –one messenger RNA-one protein”. This concept was acquired by the study of prokaryotes, essentially Escherischia coli, a microbe colonizing the human intestinal tract. The discovery in 2001 that the human genome consisted in about 35,000 genes was a surprise because this was a small number, only trice the amount of genes found in a flea. This threefold difference in the number of genes did not account for the immense difference in complexity between these two organisms. It is now clear that the genes of evolved primates are able to synthesize about three different messenger RNAs, each commanding the synthesis of a different protein. These proteins, in turn, may be remodeled later on by proteases, producing therewith an infinity of different proteins.

The superior activity of the genes of evolved vertebrates is not enough to explain the differences observed between man and chimp. Striking differences in morphology and cognitive abilities exist between humans and the chimpanzees, although the chimps are 98.7% identical in their genomic DNA sequences. It was pointed out in 1975 that the sets of proteins (and by extension the genes encoding the proteins) found in chimps and humans were also virtually identical. The differences in behavior observed between chimp and man could not be explained on the basis of the differences of their genomes. The investigators hypothesized that the differences between the two species resided in gene expression, i.e. the rate at which RNA and proteins are made, but could not prove it because the necessary tools were not developed.

A multinational research team led by S. Pääbo confirmed this intuition28. What differentiates humans from other primates is the activity of the genes in the brain. Analyzing the amount of RNA and protein produced by genes in liver, blood and brain, it was discovered that the neocortex of humans, but not the liver and blood, produced 5.5 times more RNA than was produced in the neocortex of the chimp, which in turn was much more active than that of the orangutan. Differences in RNA do not necessarily translate into differences in protein levels. It was found that the human brain produced 31% more protein than the chimp. It is quite possible that these quantitative changes occurred in three phases, correlating with the increases in brain size of H. habilis, Pithecanthropus and H. sapiens. In primates, the action in evolution is clearly in the brain.

Horrobin29 pointed out that it is not the social and environmental challenges the hominids faced that humanized them, but their response to these challenges. Their genetic responses are expressed in differences in the biochemistry of those tissues that clearly distinguish humans from primates. These tissues are the breasts, the subcutaneous adipose fat and the brain. Lipids make up 60% of the dry bulk of the brain and Essential Fatty Acids (EFA) make up 20% of it. The essential fatty acids arachidonic acid (AA) and docosaHexaenoic acid (DHA) are synthesized in the liver from exogenously supplied linoleic acid (LA) but the synthesis is too slow to fulfill the needs of an active modern human brain. A direct exogenous supply of these essential fatty acids (EFA) is preferable.

A human brain functions correctly when it has a size sufficient to increase the number of neuronal units, which may interact. But size is not sufficient: Neanderthals had a size of brain similar to that of modern sapiens sapiens, yet no artistic activity was ever convincingly demonstrated in this human culture. As important as size is the way various parts of the brain are connected together and the way various neuronal cells within a single brain area are interconnected at the micro level.

The size of the brain of evolved mammals is not uniformly proportional to the body size. Small mammals such as squirrels have proportionally bigger brains than large animals such as cows and horses. The only mammalian species that maintained a brain size proportional to the body size while globally increasing in body mass are the marine mammals, the carnivores and the primates. The incapacity by most other mammalian species to maintain a brain size increase in proportion to body mass increase is related to the scarcity of essential fatty acids (EFA) in foods. Essential fatty acids are found in the meat and organs of animals, essentially the brain and liver, in egg yolks, in algae and in the animals (crustaceans, mollusks, fish) that feed on these algae. Herbivores such as cows feeding on plants, have a poor supply of iron and Essential Fatty Acids and would have found it difficult to maintain a big brain size. Mammals feeding on other mammals, eating eggs and fish, would have a better chance to maintain a good increase in brain size during an evolutive trend toward a larger body mass. I mentioned earlier that nuts contain large amounts of fatty acids and that nuts were regularly consumed by hominids, starting with chimps. The inferior intelligence of bottle-fed premature infants, whose IQ is found 8 points below that of breast-fed premature children, may be due to the supply of EFA provided by the human milk: the brains of pregnant human mothers shrink by 3-5% in the last trimester of pregnancy. This situation continues after birth. Cow milk is poor in EFA while breast-milk is normally rich in them. Specifically arachidonic acid is a major growth factor for the human brain.

The two successive increases in brain size of hominids observed 2.5 million years ago and 500,000 years ago were accompanied by little cultural progress. The hand ax developed 2 million years ago was maintained unchanged during 100,000 generations or more. The Pithecanthropus, 500,000 years ago, used fire and modestly refined the stone tools he used but no use of bones or arrows is observed. Creativity was largely, if not totally, absent. The successive dramatic brain expansions observed during hominid evolution were presumably due to the diets, initially fish and later meat, which provided EFA, iodine and iron. Contrary to current representations of ancestors as brawny hunters bringing wildebeest home, butchering meat with stone tools, a more accurate image might be men and women wading into placid lakes, combing shorelines for fish, mollusks and seabird eggs. The acids provided by these foods are vital to fetal brain development, and brain growth and function after birth. Infant humans that lack these fatty acids show reduced cognitive ability and vision problems (the retina has the highest concentration of EFA). Although the best source of EFA is shellfish and fish, these acids are also found in brain meat and liver, but our ancestors could not support an expanding brain by eating brain alone. A 350-gram brain from a 1000-kilo rhinoceros would barely feed a party of hunters, much less pregnant and nursing women and children. In fact, many archaeological sites for the past 100,000 years are by lakes and rivers, giving to many generations of women access to fish.

These increases in brain size could be obtained by premature birth and maintenance of strong familial ties for the protection of the newborns and their mothers. This trend was stopped at the level of the Neanderthal and primitive sapiens (Bushmen, Hottentots, pertaining to the African Gatherer culture) by the restricted size of the birth canal. A superior cultural behavior marked by artistic activities was not reached at that level of hominisation.

The next cultural level, the Australian aborigine, is marked by a considerably greater consumption of fish. Abundant fat reserves were providential in times of starvation and represented a good survival edge but also favored easier immersion in water. The atavistic hatred of water displayed by primates was thereby overcome. The most striking change in cultural behavior shown by sapiens sapiens is noticed 35,000 years ago, with the abundant presence of refined artifacts, art and religion. Again, the settlements were along rivers and fish (salmon) was a prime food supply. Yet, the size of the brain did not increase: the cultural development must be related to changes in brain function and in the asymmetry of the brain.

A brain processes information. A connection is made between information stored within the brain, new information coming in, and the actions that result from this information processing. Some people are endowed with narrow skills (e.g. chess playing, sport, painting, mathematics, music, acting, singing), implying the development of only a small area of the brain, while others have broader skills and show considerable abilities across many domains (e.g. Churchill, who was a soldier, a statesman and a painter). The richer the neural connections, within areas and inter areas, the richer the possibilities of broad skilled action. Extensive connectivity depends on the ability to make and remodel phospholipids rich in essential fatty acids. The essential fatty acids, either synthesized in the liver from the extraneous linoleic acid (LA) supplied by food or else directly supplied by the diet, are transported to the brain, the breasts and the subcutaneous fat storage places by lipases and other fatty acid transport proteins. Lipases break down the fatty acids and transport them while other enzymes, the transferases and synthetases, incorporate the essential fatty acids into phospholipid membranes.

The reduced or excessive activities of these enzymes influence intelligence and mental abilities.

An increased activity of the lipases liberates essential fatty acids. This allows a faster than usual synthesis of phospholipids, resulting in better neuronal connectivity. This in turn favors manic depression, which is associated with creativity, energy and productivity.

A reduced activity of transferases results in reduced rate of incorporation of EFA into phospholipids. This induces dyslexia, associated with considerable special skills (e.g. Edison, Einstein, da Vinci). The ability to visualize shapes is a skill at which dyslexic individuals excel and the gene for dyslexia (reduced activity of transferases) may have been introduced at the Pythecanthropic level, if not even at the Australopithecine level, with the need to conceptualize the final ax hidden within a stone.

Schizophrenia occurs when both lipase and transferase abnormalities are present together, with the result that the free wandering EFA is not anymore incorporated into phospholipids. Schizophrenia is associated with sociopathy, paranoia and mental retardation but also with creativity, musical skills, energy and charismatic leadership. The two genes for schizophrenia, i.e. the gene for dyslexia (reduced activity of transferases) and the gene for manic depression (increased activity of lipases) may have been incorporated at the level of the Cro-Magnon man, which would explain the burst of creative activity observed at that time. The diet of these people, with abundant supplies of the building blocks of the brain, will largely have minimized the negative impacts of the anabolic and catabolic deviations of the lipid metabolism introduced.

On switching to an agricultural way of life, 10,000 years ago, most of the essential fatty acids disappeared from the diet and only linoleic acid continued to be supplied exogenously. The standards of living of most human beings was thereby drastically reduced. This impoverishment is well documented: the indigenous inhabitants of Florida (the Seminoles) and of the great American plains (the Cheyennes) were splendid human specimens, much healthier, sturdier and less disease-prone than the Spaniards and Anglo-Saxons who colonized them, yet their descendants rapidly declined to the poor physical level of their conquerors. The relative shortage in EFA of the diets newly introduced 10,000 years ago resulted in increases in both creative and disturbed behavior. In those days, many people with a reduced intelligence were still intelligent enough to absorb the teachings of irresponsible illuminated charismatic leaders. This trend, that has been considerably amplified these last three hundred years, is not related to gene reshuffling but to environmental factors: improved cereal processing has eliminated the bulk of EFA from the diet, cooking has eliminated vitamins, food intake of plants is restricted to a few staples and a great consumption of saturated fat (pork meat) displaces EFA from phospholipids. As a result, the severity of schizophrenia has increased, as well as the number of intellectually limited leaders reveling in assertive creeds, internal coherence of thought and primitive Logic, and the willingness of most human beings to follow them.

References

28. W. Enard et al. Intra-and interspecific variation in primate gene expression patterns. Science 296: 340-343, 2002

29. Medical Hypotheses, 50, 269-288, 1998

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