By Rebecca Searles
If ancient hominids existed today, they might have a bone to pick with their vegetarian descendants. Meat gave our distant ancestors the brain power that makes higher-level decision-making—like, becoming a vegetarian—possible, according to researchers speaking on Feb. 20 at the 2011 AAAS meeting in Washington, D.C.
The modern human brain is two to three times larger than that of our closest relatives, chimpanzees. But to supply energy to such metabolically demanding tissue, a distinct trade-off in energy allocation had to evolve.
In 1992, researchers proposed that this gradual expansion of the ancestral brain was made possible by switching from a vegetative diet to a meat-rich, fat-rich diet. As meat became a dietary staple, the gut shortened, and the brain no longer needed to rely on fuel from muscle and fat stores in the body. A shorter gut requires a great deal less energy than the lengthy gut of herbivores. Drawing on the extra energy resources from a fatty diet, and a shorter gut, the brain could afford to grow.
Greg Wray, an evolutionary biologist at Duke University, studies the genetic and molecular systems that co-evolved with this dietary shift to produce a larger brain. At the meeting, Wray laid out the case for meat and other protein-rich foods as evolutionary drivers of a bigger, more complex human brain.
“For a long time now, anthropologists have known that [diet and cognition] are connected at an organismal level,” Wray said. “But we now see that there is a connection between these two at the genetic level.”
In order for brain growth to occur, brain cells need energy from glucose, a basic sugar that fuels cellular activity. As diet changed over time, the body’s way of converting food into energy may have needed to evolve to keep up with these new, high-energy demands of the brain.
Wray’s research identified a gene that codes for a glucose transport molecule—the only known molecule that allows glucose’s entry to the brain. The human variation of this gene expresses two to three times the amount of glucose transport molecules than its chimpanzee counterpart. By examining clinical data, Wray determined this gene to be necessary for proper human brain development.
“Severe [forms of the gene] can cause genetic microencephaly, [a disease] in which no glucose can enter the brain, and it dies from starvation,” Wray said. “So this boost in the brain, we can tell, is critical for normal brain development.”
Wray’s work could have broad implications for evolutionary medicine, an understanding of health and disease from the evolutionary perspective.
“Any time you take something as poised as a metabolic system and you drag it off and make it do something different, there will be unintended consequences,” Wray explained. “Something needs to compensate. So, probably a lot of medical issues are a result of these unintended consequences.”
As for vegetarians, Wray says they’ve had plenty to say to him about his work. He has one piece of advice: Creatine is important. Creatine, a natural acid gained from eating meat, plays a critical role in cognition. Wray encourages vegans to consider taking a creatine supplement, particularly if they’re pregnant.
Rebecca Searles is a biology and psychology student at the University of North Carolina at Chapel Hill. She edits Carolina Scientific, an undergraduate research publication, and she hopes to pursue a career in science writing. She writes a blog, The Stone Age Mind, for Psychology Today. Reach her at rsearles@email.unc.edu.
