May 28, 2012 report
New research suggests apes have human-like personalities
Now new research by an international team of psychologists and animal research scientists may have settled the issue once and for all. In their paper published in the journal Animal Behavior, the team says that their study shows that yes, some apes do display different kinds of personality traits, and that chimpanzees in particular have some that are very nearly the same as us humans.
In addition to comparing personality traits in animals, researchers have of course also been studying personality traits in humans and over the years have come to a consensus that such traits can be boiled down to just five major dimensions, as they are called: agreeableness, openness to experience, extroversion, neuroticism and conscientiousness. All of us have different degrees of each which make up our general personality types. In this new research, the team used these same dimensions as a means to compare personalities between apes and to compare them to humans.
In their study, the team sent an extensive questionnaire to 230 volunteers at zoos and research centers in several countries. In it, respondents were asked to gauge forty or fifty personality items that were rated on a scale of one to seven. The raters as they were called, observed chimps and apes in action and then rated them as they saw fit. The results were then sent back to the research team who then applied statistical analyses to remove biases. Once that was done, the results showed that chimps appear to have all five personality dimensions, while orangutans seem to have just three.
Ratings of chimpanzee, Pan troglodytes, and orang-utan, Pongo pygmaeus and Pongo abelii, personality reveal dimensions resembling those found in humans. Critics have argued that this similarity derives from anthropomorphic projection or other rater-based effects. We developed two forms of data reduction analyses to determine whether these dimensions can best be explained by the inherent tendencies of the animals (e.g. orang-utans that are curious are playful) or anthropomorphic projections of raters (e.g. believing that orang-utans that are curious should be playful). We found that personality dimensions derived after differences between rater means and rater*item interactions had been removed from ratings replicated the previously discovered dimensions. Conversely, we found a different set of dimensions when analysing items from which differences between animal means and animal*item interactions had been removed. Finally, we used multilevel factor analysis to examine whether the published structure was replicated when we extracted factors based on the within-level animal differences in item scores effects while allowing between-rater differences to covary freely. Again, the personality dimensions were similar to those described in previous studies. These analyses can be used in combination with interrater reliability, temporal stability, and correlations between personality and other external variables to validate animal personality ratings. These analyses confirmed that personality similarities between humans and great apes are best explained by genetic and phylogenetic affinity and not by anthropomorphic artefacts.
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