Forget the textbook story about tool use and language sparking the dramatic evolutionary growth of the human brain. Instead, imagine ancient hominid children chasing frogs. Not for fun, but for food.
According to Dr. Stephen Cunnane it was a rich and secure shore-based diet that fuelled and provided the essential nutrients to make our brains what they are today. Controversially, according to Dr. Cunnane our initial brain boost didn't happen by adaptation, but by exaptation, or chance.
"Anthropologists and evolutionary biologists usually point to things like the rise of language and tool making to explain the massive expansion of early hominid brains. But this is a Catch-22. 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. This is what created the necessary physiological conditions for explosive brain growth," says Dr. Cunnane, a metabolic physiologist at the University of Sherbrooke in Sherbrooke, Quebec.
The evolutionary growth in hominid brain size remains a mystery and a major point of contention among anthropologists. Our brains weigh roughly twice as much as our similarly sized earliest human relative, Homo habilis two million years ago. The big question is which came first - the bigger brain or the social, linguistic and tool-making skills we associate with it?
But, Dr. Cunnane argues that most anthropologists are ignorant or dismissive of the key missing link to help answer this question: the metabolic constraints that are critical for healthy human brain development today, and for its evolution.
Human brains aren't just comparatively big, they're hungry. The average newborn's brain consumes an amazing 75-per cent of an infant's daily energy needs. According to Dr. Cunnane, to fuel this neural demand, human babies are born with a built-in energy reservoir - that cute baby fat. Human infants are the only primate babies born with excess fat. It accounts for about 14 per cent of their birth weight, similar to that of their brains.
It's this baby fat, says Dr. Cunnane, that provided the physiological winning conditions for hominids' evolutionary brain expansion. And how were hominid babies able to pack on the extra pounds? According to Cunnane their moms were dining on shoreline delicacies like clams and catfish.
"The shores gave us food security and higher nutrient density. My hypothesis is that to permit the brain to start to increase in size, the fittest early humans were those with the fattest infants," says Dr. Cunnane, author of the book Survival of the Fattest, published in 2005.
Unlike the prehistoric savannahs or forests, argues Dr. Cunnane, ancient shoreline environments provided a year-round, accessible and rich food supply. Such an environment was found in the wetlands and river and lake shorelines that dominated east Africa's prehistoric Rift Valley in which early humans evolved.
Dr. Cunnane points to the table scrap fossil evidence collected by his symposium co-organizer Dr. Kathy Stewart from the Canadian Museum of Nature, in Ottawa. Her study of fossil material excavated from numerous Homo habilis sites in eastern Africa revealed a bevy of chewed fish bones, particularly catfish.