SCIENCE DAILY
Neuroanatomical differences between the brain of the chimpanzee (left) and the bonobo (right) match what we know about the human brain and behavior. IMAGES/James Rilling
why our two closest living primate relatives, chimpanzees and bonobos, have widely different social traits, despite belonging to the same genus. Now, a comparative analysis of their brains shows neuroanatomical differences that may be responsible for these behaviors, from the aggression more typical of chimpanzees to the social tolerance of bonobos.
“What’s remarkable is that the data appears to match what we know about the human brain and behavior,” says Emory anthropologist James Rilling, who led the analysis. “The neural circuitry that mediates anxiety, empathy and the inhibition of aggression in humans is better developed in bonobos than in chimpanzees.”
The journal Social Cognitive and Affective Neuroscience published the results, the most comprehensive comparative analysis to date of the neural systems of chimpanzees and bonobos.
“By contributing to our basic understanding of how brain anatomy relates to social behavior, this study may provide clues to the brain dysfunction underlying human social behavioral disorders like psychopathy and autism,” Rilling says.
Chimpanzees and bonobos diverged from a common ancestor with humans about six million years ago, and from each other just one-to-two million years ago. Despite this relatively brief separation in evolutionary terms, the two species exhibit significant differences in social behavior. Compared with chimpanzees, bonobos are more anxious, less aggressive, more socially tolerant, more playful, more sexual and perhaps more empathic.
“Chimpanzees tend to resolve conflict by using aggression, while bonobos are more likely to use behavioral mechanisms like sex and play to diffuse tension,” Rilling says. “The social behaviors of the two species mirror individual differences within the human population.”
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