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A team of researchers from France, Germany and Belgium has found evidence that neither nature nor nurture leads to personality differences—it is the result of nonheritable noise during brain development. In their paper published in the journal Science, the group describes their study of behavior in Drosophila melanogaster (fruit flies) and what they learned.

For many years, there has been a debate in the scientific community about the underlying factors that lead to major personality differences in people—why are some people shy while others are outgoing? Or why do some follow the straight and narrow while others wind up in prison? Some argue that it is basic genetics—people inherit their personalities from our parents. Others insist that personalities develop as people grow from infancy, influenced by life experiences—people who grow up in a violent home are more likely to become violent people as adults, by this reckoning. In this new effort, the researchers have thrown a wrench into the debate by adding a third possible factor: nonheritable noise.

Prior research has shown that as humans and other animals develop, random noise can lead to noninheritable differences in brain structure. This factor leads to differences in brain structure between clones, for example. Intrigued by the idea that such noise might be the real reason for personality differences, the researchers used fruit flies as a test subject.

The work involved giving multiple fruit flies an incentive to walk on a surface toward an object. Prior research had shown that some walk right to it consistently, while others take a meandering path, also consistently—indicative of a personality difference. The flies were then divided into two groups, straight walkers and meanderers. They were then dissected with a focus on dorsal cluster neurons in the brain. Prior research has found these clusters to be involved in personality in fruit flies.

The researchers found a consistent pattern—flies that walked straight toward the object had more asymmetric wiring than did those that tended to meander. Prior research also demonstrated that such differences in neural structure are due to nonheritable noise during brain development. The researchers claim their findings provide evidence that personality differences in fruit flies may be chalked up to random noise.

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More information: Gerit Arne Linneweber et al. A neurodevelopmental origin of behavioral individuality in the Drosophila visual system, Science (2020). Journal information: Science Gerit Arne Linneweber et al. A neurodevelopmental origin of behavioral individuality in the Drosophila visual system,(2020). DOI: 10.1126/science.aaw7182

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