Individual Differences and Animal Personality

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As illustrated in the above quote by Yerkes it is commonplace to regard individual animals as possessing distinct personalities. Yerkes went on to say in that same article, “One may as readily identify a familiar ape among many by its personality as mirrored in behavior as by its physical appearance” (1939, p. 111). I am guessing that anyone with extensive contact with almost any species, certainly with any primate species, would say something similar. As a consequence of that widespread opinion, while personality may not be a topic that presently attracts much attention within comparative cognition, the study of personality in nonhumans is in fact abundant. The study of personality in animals has attracted considerable empirical attention beginning with Pavlov’s identification of personality types in dogs. Subsequent work has revealed a number of similarities in personality between humans and nonhuman animals. A number of personality traits that are typically identified in studies of human personality, including aspects of neuroticism and extraversion, have also been isolated in studies of animal personality, predominantly in studies of nonhuman primates. Even traits that might appear to be uniquely human such as conscientiousness and psychopathy have nonhuman parallels. Moreover, a number of personality traits in humans that have distinctive neurobiological signatures, particularly aspects of neuroticism, are identifiable in nonhuman primates. These similarities include low basal serotonin levels and elevated cortisol levels in response to stress. It is argued that the inclusion of personality assessments in studies of comparative cognition will identify sources of variance that affect cognitive functioning, and will identify mutual influences between personality and cognition.