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Personality differences in capuchin monkeys

No one is alike. This is true not only for us, but for monkeys as well. A new study published in the Journal of Research in Personality has demonstrated that the adult capuchins monkeys hosted at the ISTC-CNR of Rome exhibit pronounced individual differences in a broad range of behaviours . An international team of researchers from the ISTC-CNR and Free University Berlin, Germany —psychologist Jana Uher and her CNR-collaborators, the biologists Elisabetta Visalberghi and Elsa Addessi—applied a novel approach to measure personality traits in monkeys.

Most personality research on humans is done using self-reports in questionnaires. But these methodologies have many drawbacks because people usually do not have an accurate perception of their own and others' behaviours and their psychological underpinnings. Previous animal studies that adopted personality questionnaires developed for human individuals or that restricted the behavioural investigation of animal individuals to just a few personality traits. In contrast, this study used a complex procedure involving 15 behavioural tests in which each capuchin monkey was examined individually as well as methodical behavioural observations of each monkey when it was together with its group members. Moreover, this entire procedure was systematically repeated over time.



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Striking individual differences in most of the capuchins' behaviors were demonstrated. The study measured 146 behavioural variables that led to identify 21 personality traits. For example, some individuals explored novel objects, novel foods, and changes in the environment quickly and intensely, whereas others were very cautious and reluctant to inspect them. When presented with a large bed sheet hanging between two horizontal poles, one much higher than the other, a male, Sandokan used it as a slide many times. In other words, he was ready to exploit the novelty of the situation to create a new game. In contrast, Vispo, another male of his group, tried all possible ways to avoid any contact with the sheet; in fact, he started walking bipedally when he moved over the poles! As is the case for humans, there were all possible intermediate variations of behaviour between these two extremes.

Very interestingly, individual differences in behavior were stable over time. Moreover, personality was differences are largely unrelated to sex and also to age. Despite the fact that capuchins ranged from 8 to 32 years, age played no role, since only impulsiveness declined with age!

How do these results compare to those in humans? According to Jana Uher "Stable individual differences are not uniquely humans but can be found in other species as well, including capuchins a species whose common ancestors with humans dates back to 35 million years ago. Our finding that capuchins, a group living species in which males are bigger than females, do not exhibit pronounced differences in personality traits, as frequently hypothesized for our human ancestors may shed new light on the causes and consequences of sex and gender differences in humans."

What is next?? The research team is now analysing how "capuchinologists", i.e. researchers and students who have spent months or years studying the monkeys of our Center and/or capuchin monkeys all around the world assess the personalities of their monkeys and how this matches with behavioral results.

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