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"Personality" differences but no sex differences in the individual behaviour of four monkey species from three different continents
In their appearance, the sexes differ from one another in many animal species. Males are often bigger and physically stronger than females. But sex differences in body morphology need not go along with sex differences in behaviour as a recent study on monkeys showed. In each of four species, stable individual behavioural differences-thus, "personality" differences-occurred but sex differences were largely absent. These findings shed new light on many evolutionary psychologists' assumption that sex differences in human behaviour inevitably result from the bodily differences between men and women and thus constitute an evolutionary heritage of humans.
Because fossil bones do not reveal much about the social behaviour of their former carriers, scientists often seek to find evidence for their evolutionary theories from research on modern humans. Most findings on gender differences in "personality" derive from research using questionnaires. Questionnaires can capture what humans think of themselves and of others, but they cannot capture the peculiarities and differences that can actually be observed in individuals' behaviours. Therefore, questionnaire answers cannot be used to unravel whether gender differences in human individual behaviour are culturally influenced or whether they are, in fact, biologically determined or even evolutionarily derived as often assumed. Ultimately, making conclusions from modern humans' behaviour to that of their evolutionary ancestors and using these conclusions, in turn, to explain modern humans' behaviour remains circular. Possible mistakes cannot be detected.
In a recent study in the Berlin Zoo and the Animal Shelter of Berlin, Germany, Jana Uher and her research team have studied individual behaviours in four monkey species. These species are endemic to three different continents: Weeper capuchins originate from South America, Mandrills from Africa, and toque macaques and rhesus macaques from Asia. The study is based on a novel research paradigm that the personality expert has developed to explore "personality" differences independently from everyday language and thus also in nonhuman species (see the Science Blog "A new scientific paradigm for research on individuals").
In this new research, Jana Uher adapted and further developed approaches from cross-cultural "personality" psychology for the purposes of systematic cross-species comparisons of "personality" differences. To test these novel methodologies, her team observed individual monkeys of each of the four species over 4-5 weeks, each
individual for in total 60-80 hours. The researchers recorded grooming, body contact and proximity to conspecifics as well as aggressive and dominant behaviours. In all these behaviours, pronounced and temporally stable individual differences occurred that are commonly called "personality" differences
(see the Science Blog ""Personality" differences compared between four monkey species:
A novel methodology to unravel communalities and differences").
In a previous study conducted with her research collaborators in Rome, Italy, the personality expert has investigated four groups of tufted capuchins over longer periods of time. These South-American monkeys also showed pronounced "personality" differences in their behaviours but hardly any sex differences. "Meanwhile, we have data from eight social groups of monkeys from five different species in which we found stable individual differences but hardly any sex differences in behaviour", she says (see the
Science Blog "Sex differences, not as universal as previously
"There is no doubt that questionnaire assessments are biased by stereotypical beliefs. But in which kinds of judgements these biases occur and in what ways they influence the assessment outcomes, seems to be quite different. This complicates the current picture of findings. We urgently have to explore, how people generate their answers to standardised questionnaires. Otherwise, all questionnaire data are meaningless", Jana Uher warns.
This research is part of a project funded by the German Research Foundation
Uher, J. (2015e). Comparing individuals within and across situations, groups and species: Metatheoretical and methodological foundations demonstrated in primate behaviour. In D. Emmans & A. Laihinen (Eds.). Comparative Neuropsychology and Brain Imaging (Vol. 2), Series Neuropsychology: An Interdisciplinary Approach. (chapter 14, pp. 223-284). Berlin: Lit Verlag. [Download] ISBN 978-3-643-90653-3 DOI: 10.13140/RG.2.1.3848.8169
Last update: 14.09.2015
Keywords: Weeper capuchin (Cebus olivaceus), Mandrill (Mandrillus sphinx), Toque macaque (Macaca sinica), Rhesus monkey (Macaca mulatta), macaques, personality, rating, judgment, personality questionnaire, individual differences, species differences, species comparisons, personality dimensions, personality traits, individual behaviour, individual-specific behaviour, individual behavior, despotic, egalitarian, dominance hierarchy, aggressiveness, social behavior, social orientation.