The size of the human brain in relation to the body weight is much bigger than that of any other primate. Our brains weigh roughly twice as much as the earliest human relative. We simply are some primates with huge brains maneuvering relatively small bodies. But what made possible this evolution of the brain size?

"Something had to start the process of brain expansion and I think it was early humans eating clams, frogs, bird eggs and fish from shoreline environments," said Stephen Cunnane, a metabolic physiologist at the University of Sherbrooke in Quebec and author of a new study on this problem.

Comparing the human newborns with ape babies one sees a startling difference: human babies are fat. The baby fat accounts for about 14 % of their birth weight. And what is more interesting is that all this fat is consumed almost entirely to feed the development and growth of the brain. Human baby fat provides the energy source for the rapidly growing infant grey matter and assures a greater concentration of DHA, a substance critical to proper neuron function. Moreover, three quarters of the energy the baby receives from food also goes to the brain.

"Given that babies are helpless, that sounds like a lot to spend on an organ that is cognitively useless and does little to ensure a child's survival", Cunnane said.

And what made it possible for human babies to be born with so much fat? According to the scientist it was a diet that included fish and shellfish, particularly frogs and eggs. Such food had been the best source of nutrients and minerals to foster brain development. In fact it still is today. Deficiencies in iodine and iron, minerals rich in a fish diet, can lead to cognitive degeneration. That's why companies added iodine to salt starting in the 1920s.

When one looks at a chimps' diet, one sees that it is low in "brain food". If scientists fed them fish, Cunnane said, their brains might grow. However, he added, "We'd never see the results. The experiment would take tens of thousands of years of evolution. But I think there would be a change in chimp brains."

The question now is why did humans started to eat fish? Was this change of diet just a matter of accident?

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Trivia: What animals have a similar or a bigger brain in relation to their body weight than humans? Animals such as the porpoise, the rat, the vampire bat, and the crow.
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