| Given the biological continuity between humans and other animals, it would seem obvious to ask whether there are dimensions of personality common to a wide range of species. Unfortunately, however, there is no unified body of research on animal personality that could answer this question; instead, the literature on animal personality is fragmented across the fields of agricultural science, animal behavior, anthropology, psychology, veterinary medicine, and zoology. My review of more than 70 animal-personality studies illustrates the breadth and diversity of the species studied, traits examined and methodologies used. Unfortunately, the methodological diversity of studies hampers attempts to compare them quantitatively. Thus, I present a conceptual integration of studies that have examined personality structure in 12 species, ranging from octopuses, guppies, and rats to gorillas and chimpanzees. This integration reveals some striking cross-species similarities, despite pronounced differences in observational and analytical methods. I next consider arguments against and in favor of cross-species generalizations and suggest three guidelines to facilitate a judicious approach to cross-species comparisons in personality psychology: (a) use appropriate species for the comparison of interest, (b) aim for converging evidence from several species, and (c) distinguish between the phylogenetic approach and the analysis of adaptation. Next, I present an empirical study of 34 spotted hyenas ( Crocuta crocuta) which found that (a) hyena personality traits were rated by four observers with reliabilities as high as in studies of humans, (b) five broad dimensions (Assertiveness, Excitability, Human-directed Agreeableness, Sociability, and Curiosity) captured about 75% of the total variance, (c) this dimensional structure could not be explained in terms of the animals' dominance status, sex, age, or appearance, and (d) as expected, female hyenas were more assertive than males. I conclude by proposing a research agenda for a comparative approach to personality that eventually can help understand the genetic, biological, and environmental bases of personality, as well as providing useful ways to examine personality change, personality types, and the formation of personality impressions. This agenda would complement, rather than replace, current research on human personality. |
