A longitudinal study of personality in non-human primates

Longitudinal studies of human personality have been very fruitful, proving the continuity of certain traits from childhood to adulthood, or personality development related to social conditions. Even though non-human primate personality has been studied for at least 20 years, almost all of the research done has focused on the description of personality dimensions and their correlation with biosocial variables. Very few have been longitudinal studies. But, from these last ones, it has been found that some personality dimensions remain constant in time and others do not. In other words, personality evaluation has a predictive value in time and across situations. The objective of this study was to evaluate, in two different periods, several personality traits in non-human primates in search of personality consistencies or changes. So, twice in a period of 8 years, the personality of 20 captive stumptail' macaques (Macaca arctoides) was evaluated. A Factor Analysis classified individuals in 4 dimensions: DOMINANT, SUBMISSIVE, EXTROVERT and ALTRUIST. This classification was corroborated with a Discriminant Analysis. Finally, a Wilcoxon Rank Analysis determined if the changes in personality traits between one period and the other were significant. Similarly to other studies, we found that most subjects changed,which can be due to the important biosocial changes occurred in individuals in such a long time between periods. Interestingly, only some traits within the personality dimensions changed significatively, which may indicate a qualitative difference among them, that is, a difference between temperament and character traits.