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Challenging The Social Brain Hypothesis With A Very Fruity Theory

First Posted: Mar 29, 2017 04:00 AM EDT
A Primate
The reason behind the evolution of brain size in primates is yet to be pinpointed.
(Photo : Wochit News/YouTube screenshot)

Primates have the most evolved brains in the animal kingdom that makes them somewhat superior from the rest. Evolutionary biologists have been trying to identify the factors that triggered the formation of larger brains and improved cognitive abilities in humans and apes. Up until now, the "social brain hypothesis" was considered the most plausible explanation regarding the same.

The social brain hypothesis states that higher primates started living in groups that involved maintaining complex relationships. The more they tried to fit in these groups and form social relationship, the more pressure it exerted on their brain. The pressure itself stimulated growth of the brain to suffice for the increased demands of functioning.

However, a recent study published in the Nature Ecology & Evolution journal indicates that the theory may have some loopholes. The lead author of the study, Alex DeCasien from the New York University, tried to study the role of polygamy in determining the size of the brain. Surprisingly, DeCasien found that polygamous behavior that can be considered synonymous with maintaining complex social relationships had little impact on the size of the brains when compared to the brain size of monogamous primates, Science reported.

On the contrary, the size of the brain was largely dependent on the diet. It was observed that those primates who were frugivores (fruit eaters) had larger brain size as opposed to the ones whose diet mainly consisted of leaves.

Researchers are of the opinion that since fruits are filled with natural sugars and vitamins, they provided the instant energy required for the development of the brain. On the other hand, leaves are hard to digest and thus low in nutritional output, which explains the smaller brain size in leaf-eating primates, Business Standard reported.

However, why was all the extra energy obtained from fruits channelized for the development of the brain and not of any other body parts is a question that DeCasien's theory fails to explain. Expert researchers are of the opinion that considering a single factor or evolutionary change as the sole reason behind a trait is not a wise thing to do. It seems fruits may have supplied the energy required for brain development, but the process may have been stimulated due to intricate social relationships.

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