Brain food

If you are reading this, you might want to thank Homo erectus, or others of our early ancestors who learned how to do two things: eat meat and cook their food. Those dietary advances likely jump-started the evolution of the big, efficient brain that makes us Homo sapiens.

Two recently published scientific studies have added to evidence that the boost in available dietary nutrients gained by cooking foods, and particularly from cooking meats, provided the extra energy and social changes leading to the modern human brain.

Results of one recent study, published last month in the journal Proceedings of the National Academy of Sciences, compared the brain sizes of various primates along with the time each spends, or spent, on feeding each day. The brain, it turns out, requires considerable fuel to function – the human brain claims about 20 percent of the human body’s resting energy consumption.

But there is only so much a primate can eat, and only so many hours in the day in which to eat it. Gorillas are much larger than humans, but have smaller brains with fewer neurons. They spend most of their days eating raw vegetables in order to metabolize enough energy to fuel their bodies. So did our early ancestors such as Homo habilis.

The study, from researchers at the University of Rio de Janeiro in Brazil, found that “such a metabolic limitation was overcome in the human lineage by the advent of cooking food, which greatly increases the caloric yield of the diet, as a result of the greater ease of chewing, digestion, and absorption of foods.” They also note that the earlier addition of raw meat to the diet of earlier hominins may also have contributed to increase its caloric content, raw meat is difficult to chew and ingest, whereas cooked meat is easier to chew and has a higher caloric yield.

In addition, they found that cooking “would also have increased the time available for social and more cognitively demanding activities, which in turn would impose a positive pressure for increased numbers of neurons, now affordable by the new diet.”

Another research report, based on archeological studies in the Olduvai Gorge in Tanzania, recently was published in the online scientific journal PLOS One. In this study, researchers examined a 1.5-million-year-old skull of a malnourished hominin child. 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.

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 analysis of the role of diet in human evolution, read “Catching Fire: How cooking made us human,” a book by primatologist Richard Wrangham.

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