Like us, chimps and bonobos differ

EMORY (US) — Similar to humans, chimps and bonobos have widely different personalities, despite diverging from each other a relatively short one to two million years ago.

A new study comparing their brains shows neuroanatomical differences that may explain why chimpanzees are anxious and aggressive and bonobos are socially tolerant and playful.

“What’s remarkable is that the data appears to match what we know about the human brain and behavior,”says James Rilling, associate professor of anthropology at Emory University.

“This study may provide clues to the brain dysfunction underlying human social behavioral disorders like psychopathy and autism.”

Details of the research are reported in the journal Social Cognitive and Affective Neuroscience.

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.”

Rilling heads Emory’s Laboratory for Darwinian Neuroscience that uses non-invasive neuro-imaging technology to compare the neurobiology of humans and other primates. The lab draws on resources of Emory’s Yerkes National Primate Research Center.

“In addition to exploring links between neuroanatomy and different social behaviors, we’re mapping the underlying biology for how species evolve and differentiate,” he says.

A variety of imaging and analytical techniques were used in the chimpanzee-bonobo study, Rilling says.

Voxel-based morphometry compared the gray matter in standard structural scans of the brains. Diffusion tensor imaging (DTI) captured the white matter connections, to compare the fiber tracts that wire the brain.

Bonobos have more developed circuitry for key nodes within the limbic system, the so-called emotional part of the brain, including the amygdala, the hypothalamus, and the anterior insula.  The anterior insula and the amygdala are both implicated in human empathy.

“We also found that the pathway connecting the amygdala and the prefrontal cortex is larger in bonobos than chimpanzees,” Rilling says.

“When our amygdala senses that our actions are causing someone else distress, we may use that pathway to adjust our behavior in a prosocial direction.”

Chimpanzees have better developed visual system pathways, according to the analysis. Previous research has suggested that those pathways are important for tool use, a skill which chimpanzees appear better at than bonobos.

Researchers from Oxford University contributed to the study.

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