Brain chemical differences suggest possible reason for humans having social edge over other primates.

A team of researchers affiliated with several institutions in the U.S. has found some key differences in brain chemicals between humans and other primates. In their paper published in Proceedings of the National Academy of Sciences, the group suggests these differences could explain the social edge humans have over other primates.

Scientists have studied the anatomy of humans and other primates for many years as part of an effort to understand why we humans came to be so dominant. Many assume that it is not just brain size, because prior research has shown that our early ancestors began engaging in advanced activities before our brains grew larger. This, the researchers note, suggests that our ancestors developed different brain chemistry. Brain chemicals play a role in such behaviors as socializing, which logically could lead to better language and other skills. To test this theory, the researchers studied brain chemistry in six species: humans, macaques, baboons, capuchins, chimpanzees and gorillas. Samples for the non-humans were gathered from animals that had died naturally in zoos.

The team studied nerve cells from the striatum, which serves as a relay for chemicals in the brain, looking for neurotransmitters, most specifically serotonin, dopamine and neuropeptide Y—they have all been tied to social and cooperative behavior. Doing so revealed brain levels of each when the animal was alive.

The researchers found that humans and great apes had higher levels of neuropeptide Y and serotonin in their basal ganglia than the other primates. They also found that humans had more dopamine in the striatum than the apes but less acetylcholine than chimps or gorillas. It is these differences, the group claims, that sets us apart from other primates. They suggest such differences would have made our ancestors more social, leading to a host of evolutionary changes.

Interestingly, a separate study was done recently by a team at Kent State—they were looking to explain the demographic success of humans and as part of that research found that female survivorship was a key component. They suggested differences in female brain chemistry led to females mating more often with males who were more outgoing but who were not too aggressive. Such males, they further suggest, would have been better providers because by that point in history, hunting was done in groups.

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