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Abstract

The evolutionary origins of human handedness are still unknown. The study of lateralized behaviour in our closest relatives, the nonhuman primates, is therefore useful to clarify how this trait appeared and evolved in our species. In the present study, lateralized behaviour was assessed in a population of 32 free-ranging Mexican mantled howler monkeys (Alouatta palliata mexicana) for thirteen spontaneous motor patterns, at both individual and group levels, as well as the effect that age, sex and posture have on its strength and direction. The studied population of howler monkeys displayed only few significant lateral biases at the individual level with some motor patterns (Binomial tests, p ≤ 0.05). No biases towards the use of a particular limb or side of the body were found at a population level. Therefore, even though some individuals showed significant limb/side preference with some motor patterns, no signs of task specialization, manual specialization, or even true handedness were found. Similarly, no effects of sex, age or posture were found on the direction or strength of lateralized behaviour. The general absence of limb/side preferences found in this population may be due to the constraints imposed by the arboreal life and/or the type of diet. Possible causal agents of the few significant individual biases in some motor patterns found here may be the presence of internal and/or external handicaps and experience. Further research is needed in order to assess whether the lack of human-like handedness found in the present study is only specific to the studied population, or a more general phenomenon of the genus Alouatta, or perhaps all the Platyrrhini.


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Last updated: 06/30/15