Primate brain sizes may be due to a fruit-rich diet rather than the "social brain hypothesis" that brain evolution is driven by socialization, suggests a new study.
New York University researchers analyzed the brain sizes and diets of more than 140 primate species, including apes, monkeys, lemurs, and lorises, reported National Public Radio. They discovered that primates eating fruits instead of leaves had 25 percent more brain tissue, even after controlling for body size and species relatedness.
The study was recently published in the journal Nature Ecology and Evolution.
"Are humans and other primates big-brained because of social pressures and the need to think about and track our social relationships, as some have argued?” asks James Higham, an assistant professor in New York University's Department of Anthropology.
"This has come to be the prevailing view, but our findings do not support it — in fact, our research points to other factors, namely diet," Higham added.
Stephen Montgomery, a brain and behavioral evolution researcher at the University of Cambridge, told NPR that size of social groups do not always correlate with bigger brains because primates are really diverse in behavior and habitat.
Montgomery, who was not involved in the New York University study, said that while a complex social life might drive one species to evolve bigger brains, another species' brain size might be influenced by other factors, like diet.
Alex DeCasien, a New York University doctoral candidate and lead author of the study, said the complex strategies, social structures, and cognitive abilities, are all likely to have co-evolved throughout primate evolution.
"However, if the question is: 'Which factor – diet or sociality – is more important when it comes to determining the brain size of primate species?' then our new examination suggests that factor is diet," said DeCasien.
The researchers said the study's results don't reveal an association between brain size and fruit or protein consumption on a within-species level; rather, they note, they are evidence of the cognitive demands required by different species to obtain certain food.
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