Around 6 million years ago, primates started moving from tropical forests into the savannahs. Unlike today, these prehistoric expanses were humid and probably provided a year-round supply of fruit and vegetables. But then, some 3 million years ago, the climate changed and the savannahs — along with their plentiful food supply — dried up.
Many mammals, including some primates, went extinct, but others adapted. Archaeologists working at sites in modern Ethiopia have discovered animal remains that date back almost 2.6 million years. The telltale cut marks on their bones are almost certainly signs of butchery1, says Manuel Domínguez-Rodrigo, a palaeoanthropologist at Complutense University in Madrid.
Only two types of primate survived the climate catastrophe, says Domínguez-Rodrigo. There was a “plant-processing machine on the one hand and a meat-eating machine on the other hand”, he says. “The meat-eating machine evolved a bigger brain.”
The meat-eating machine became us.
To build and maintain a more complex brain, our ancestors used ingredients found primarily in meat, including iron, zinc, vitamin B12 and fatty acids. Although plants contain many of the same nutrients, they occur in lower quantities and often in a form that humans cannot readily use. For instance, red meat is rich in iron derived from haemoglobin, which is more easily absorbed than the non-haem form found in beans and leafy greens. Furthermore, compounds known as phytates bind to the iron in plants and block its availability to the body. As a result, meat is a much richer dietary source of iron than any plant food (see 'Meat efficiency'). “You would need to eat a massive amount of spinach to equal a steak,” says Christopher Golden, an ecologist and epidemiologist at Harvard University in Cambridge, Massachusetts.
The implications for cognitive health are huge. There is a clear, but underappreciated link between meat and the mind, says Charlotte Neumann, a paediatrician at the University of California, Los Angeles, who has studied meat eating in Africa and India for the past three decades. Deficiencies in the micronutrients found in meat have been linked with brain-related disorders, including low IQ, autism, depression and dementia. Iron is crucial for the growth and branching of neurons while in the womb; zinc is found in high concentrations in the hippocampus, a crucial region for learning and memory; vitamin B12 maintains the sheaths that protect nerves; and omega-3 fatty acids such as docosahexaenoic acid (DHA) help to keep neurons alive and to regulate inflammation.
To read the rest of this article, see the Nature website:
Gupta, S (2016) Brain food: Clever eating. Nature 531, S12–S13 (03 March 2016) doi:10.1038/531S12a Published online 02 March 2016