If our early ancestors hadn’t begun eating meat around two million years ago, we might still be swinging from trees and digging up roots with our fingers. That’s one implication of a recent research report based on archeological studies in the Olduvai Gorge in Tanzania.

The research, based on a 1.5-million-year-old skull of a malnourished hominin child, was published this week in the online scientific journal Plos One. The skull shows signs of porotic hyperostosis, a form of anemia caused by deficiencies in vitamins B9 and B12, which likely occurred at weaning, according to the researchers. They theorize that by the time the child lived, our hominin ancestors had become regular meat eaters, which resulted in evolution of larger brains and more social organization. A period of scarcity of animal proteins could have negatively altered the nutritional content of the child’s mother’s breast milk or the child’s own diet to the extent that her nursing child ultimately died from malnourishment.

Earlier research has suggested that regular consumption of meat helped trigger evolutionary changes in our early ancestors such as Homo erectus and Homo habilis, with the boost in dietary energy allowing development of a larger brain, eventually leading to emergence of Homo sapiens, or modern humans.

In a Live Science article, lead researcher Manuel Domínguez-Rodrigo, from the University in Madrid, says the findings from Olduvai Gorge suggest that "human brain development could not have existed without a diet based on regular consumption of meat." He adds that regular consumption of meat at that time implies humans were hunters by then, as scavenging only rarely provides access to meat and is only feasible in African savannas on a seasonal basis.

"I know this will sound awful to vegetarians, but meat made us human," Domínguez-Rodrigo says.

For an interesting discussion of the role of diet in human evolution, read Catching Fire: How Cooking Made Us Human a book by primatologist Richard Wrangham.