How fish made us human

 

We all know that eating fish makes you clever; now it is being argued that seafood is actually responsible for the evolution of the human mind, writes Dick Ahlstrom.

A regular diet of oysters, fish and other seafood may be the evolutionary source of our big brains. Ancient humans likely feasted on the bounty along the coast, in turn taking in the fatty acids that may have boosted human brain power.

So argues Dr Michael Crawford, founder and director of the Institute of Brain Chemistry and Human Nutrition, London Metropolitan University. He believes that our evolutionary advance received a helping hand when our diets became rich in the omega 3 essential fatty acid, docosahexaenoic acid (DHA).

DHA-rich foods would have been lying there for the taking by migrating early humans who would have expended very little energy to tap into this food source, the scientist states.

Crawford was a keynote speaker earlier this week at the 2007 World Seafood Congress currently underway at the Croke Park conference centre in Dublin. He will also participate later today in the Congress's "Great Debate" on whether DHA directly from fish is better than DHA supplements.

More than 400 delegates have attended from around the world to hear talks about sustainability, human health and nutrition. The event was jointly organised by BIM, the Food Safety Authority of Ireland and Enterprise Ireland.

Crawford's argument holds that fats, or lipids, were and still are "principle determinants in evolution". The Cambrian explosion 600 million years ago, which saw the greatest development of new species yet seen, occurred after oxygen concentrations in the air reached a level where aerobic metabolism "becomes thermodynamically possible", he says.

Associated with this avalanche of new species was the emergence of differentiated cells dependent on lipid membranes. These lipids were enriched by fatty acids such as DHA and despite 600 million years of evolution since the Cambrian, DHA is still central to the development of nervous system tissues in species as diverse as fish, birds and mammals.

The marine environment was the source of DHA for this "extreme conservation" across species and its availability changed existing photosynthesisers. "The photoreceptors which had been photosynthesysing sunlight switched to converting photons into electricity. That was the beginning of the evolution of the nervous system and the brain," Crawford says.

DHA is the principle structural component that sustains the photoreceptors that allow vision. "This is a pretty powerful argument to say that DHA was central to vision and the brain."

A disparity emerged between animals that pursued marine-based diets and land-based diets, he says. Land-based food sources such as meat provide lots of protein for large bodies, but only small amounts of lipids for brain-building. For this reason, the ratio of brain to body diminished in land-locked species.

He cites as example the zebra, which has a 350gm brain and a similar weight dolphin which has a 1,800gm brain. "The dolphin has access to a rich source of DHA." So too did the early humans, who, though closely related to their primate cousins, migrated five to seven million years ago to the coast where there was both clean water and plentiful supplies of easy-to-reach seafood.

"Homo sapiens found an ecological niche where brain-building materials were readily available," says Crawford. The DHA provided by these foods helped the human brain to develop more quickly than the DHA-poor diet consumed by primates that remained on the savannah.

Crawford believes seafood was so bountiful that all members of an early human troop would have had similar access, something that was particularly important for females. "A woman even heavily pregnant would have been able to wander along the coasts and harvest this plenty."

They would have eaten well during pregnancy while carrying children who in turn also benefited from a DHA-rich environment in the womb.

"The evolution of the brain would really depend on female nutrition," he states. "There is very good evidence that maternal nutrition even before pregnancy is important for later foetal outcome."