What gave rise to the rapid brain size increase that made us ‘thinking' men? The answer: we began eating fish

One of the puzzles in biology is how rapid the human brain developed.

It took hardly a million or so years for us to become the “thinking man” or homo sapiensfrom our immediate ancestors and cousins, the homo habilis, erectusorrudolfensis. How do we know this?

From a comparison of the brain to body ratio. While the other homoshad a brain volume of 600-800 ml (based on skull size), we have about 1250 ml, and all for roughly the same body size.

Thus, we have far more within our head than our immediate ancestors or the chimpanzees (brain about 410 ml).

Brain:body ratio

These are values for adults. When we compare the brain: body ratio of newborns, the values do not differ among these hominoid species.

A new born human baby has the same head and brain size as that of the chimp. We humans grow our brains rapidly post-natally, while the others do not.

What then is the origin of this rapid brain size increase? How did this happen two million years ago (when we emerged from the other primates and homos)? The answer, curiously, appears to be – we began eating fish.

Recent paper

A recent paper by Dr. David Braun and colleagues in the June 1, 2010 issue of the Proceedings of the National Academy of Sciences, USA, reports on the historical evidence of a large collection of fish bones near a putative settlement of homo, dated to about 1.95 million years ago, in the Rift Valley of Africa. This is the area from where we humans are thought to have originated.

And the fish bones they found had bite marks matching those of human (and not great ape) teeth.

Why is this paper important? For this, may I refer you to an excellent review article by Drs. C L Broadhurst, S.C. Cunnane and M A Crawford that appeared 12 years ago in the British Journal of Nutrition (1998; 79:3-21), a review that reminds us of the logic of Sherlock Holmes?

They hypothesize that the unique geological and ecological environment of the East African Rift Valley provided an equally unique nutritional resource for the enlargement of the human brain, culminating in homo sapiens.

They ask: “how in this remarkably short stretch of evolutionary history did our intelligence arise? While many physical (i.e. bipedalism, speech), ecological (adaptation to omnivorous diet, drier climate) and cultural adaptations (use of tools, living in groups) have roles, they are not sufficient to account for the unique intelligence and culture we have today. If these adaptations alone were sufficient, then in all cases we must ask ourselves why no other primates developed as such”.

Their answer to this question is that hominids either scavenged or caught fish and included them in their diet. And it is the nutritional content in the tropical fish that helped human brain development. This helped increase intelligence enough for them to fish more often and more successfully. And for the growing human baby, the nutritional content in fish becomes vital to increase and maintain a high brain:body ratio.

Note in this context that the great apes — Chimpanzees or gorillas — are almost totally vegetarian. Except for an occasional meal of insects, tiny animals, or turtle, they are herbivorous.

Also note that fish contain those vital nutrients that the brain needs in order to develop and grow. The human brain is “oily”, containing as much as 600g of lipid per kg, with long chain fatty acids like arachidonic acid (AA) docosa-hexenoic acid (DHA), that the body does not produce; they are thus “essential nutrients” – and fish have them in good measure.

So then, where do vegetarians get their essential lipids from?

From green vegetables, walnuts and peanuts, sesame and mustard, cotton, sunflower and other oil sources. And this is why modern-day nutritionists insist on our intake of poly-unsaturated fatty acids (PUFA), rather then Dalda or trans-fats.

Not the type

Note too that meat (pork, beef, chicken and such) is muscle or protein-rich. The fat content meat has is not the type that feeds the brain. It is, as my granddaughter Kimaya says, “body food” while nuts, fish or greens are “brain food”. Thus in having chanced upon eating fish, homos had struck the jackpot, in comparison to the largely veggie primates or the carnivorous animals in the neighborhood.

What was the neighborhood? It was the cradle of human evolution – the East African Rift Valley. Geological and climate changes between 14 and 19 million years ago generated the unique ecology there, and near the end of this Miocene period, Africa became cooler and drier. The lakes Malawi, Tanganyika and Victoria became the areas or transition zones for living.

Geologists call them ‘failed oceans'. And the drop in forests into terrestrial wastelands drove the shift from tree-climbing quadrupedalism into terrestrial bipedalism.

The food sources were essentially whatever greenery there was, and water from the lakes. And in these alkaline, salty lakes that tropical fish spawned and spread. One did not even need any technology such as nets or rods to catch them; one could simply pick them by hand.

And it is the brain food that these tropical freshwater fish and shell fish that catered to the homos around; a beautiful case of the environment dictating the life of organisms around it.

And we humans came out of it – all brainy and smart. We still see it reflected in the zeal with which Bengalis eat catfish cooked in mustard oil.

dbala@lvpei.org

Keywords: biologybrain foodfishscience

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