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Primate Brain Sizes Proportional To Fruit Intake, Study Shows

First Posted: Mar 29, 2017 04:30 AM EDT
A Primate Eating Fruit
Fruit may have caused primate brain growth.
(Photo : NewsBeat Social/YouTube screenshot)

Primates such as monkeys, apes and humans have among the highest brain-to-body-size ratios compared to other animals. The same goes for other notably bright creatures like dolphins, whales and elephants.

For decades, scientists believed that the size of animal brains increase depending on their increased social complexity. This hypothesis stated that interacting and functioning with a group of the species boosted brain sizes. However, new research suggested that this is not the case.

According to Scientific American, diet was more likely instrumental in the evolution of the primates' brains. Specifically, it seems that humans as well as our primate cousins owe our relatively large brains to the fruit we consume.

The study that was published in Nature Ecology & Evolution explored the social hypothesis and found that the results were inconsistent, as the often-cited studies that supported the theory suffered from small sample sizes and flawed designs. The new work, meanwhile, based its study on a primate sample over three times larger than the previous one and used a more accurate evolutionary family tree.

It was found that dietary preferences, especially fruit consumption, became more influential in determining brain sizes, not the social factors as originally thought. Alex DeCasien, a doctoral candidate in anthropology and the lead author of the study, explained that larger brains can no longer be associated with social complexity. Instead, it resurrects older evolutionary ideas that showed the relationship of foraging and brain size.

In fact, as pointed out by Science, the only factor that seemed to have predicted the species with larger brains was based on the animals' diet -- whether they consume more leaves or fruit. Robin Dunbar, an evolutionary psychologist from the University of Oxford and one of the original authors of the social brain hypothesis, said these results were not surprising.

Eating leaves will have primates lying around for hours with their energy focused toward digestion. Fruit eaters, on the other hand, get a jolt of calories and denser amounts of nutrients, which benefit the brain more than any other body part.

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