Four million years ago, our hominin ancestors’ appetite for fat could be what delivered the energy needed to develop big brains and evolve into modern humans, anthropologists suggest.
In a paper published in the journal Current Anthropology, they theorise that our early ancestors, long before they developed tools with which to hunt and eat meat, smashed open bones left by predators to eat the fat- and nutrient-rich marrow sealed inside.
“The reservoirs of fat in the long bones of carcasses were a huge calorie package on a calorie-poor landscape,” says lead author Jessica Thompson from Yale University, US.
“That could have been what gave an ancestral population the advantage it needed to set off the chain of human evolution.”
As well as feeding a nutrient-hungry brain, developing a taste for marrow could have led to cravings for fat. Together, these forces could have driven our ancestors to make sharp, flaked stone tools and hunt large animals, the authors suggest.
The human brain comprises 60% fat and gobbles up 20% of the body’s energy at rest – twice that of other primates. Scientists have long puzzled over how human ancestors consumed the calories needed for developing and feeding larger brains.
Thompson and colleagues argue that lean meat, by itself, would not have delivered the fat needed for brain growth; they propose that rather than analysing complete bones, anthropologists should be collecting shattered pieces and asking what broke them.
Michael Crawford, founder and director of the Institute of Brain Chemistry and Human Nutrition at London Metropolitan University, UK, agrees that fats are central to the human brain’s evolution.
He contends that the essential fat omega-3 fat docosahexaenoic acid (DHA) from seafood, which would have required relatively little energy expenditure to source and eat, was the critical fat involved.