Between-species variation in the development of hand preference among macaques

This research examined between-species variation in the development of hand preference among Macaca. Specifically, we examined hand preference using juveniles and adults of three macaque species that differ in social and reactive tendencies in order to examine whether the correlation between temperament and handedness that has been noted within Macaca mulatta occurs between closely related species. Each of the species studied exhibited a different pattern of hand preference development. Both juvenile and adult M. mulatta exhibited group-level left-hand bias. Juvenile Macaca nemestrina were not biased towards either hand at the group-level, whereas adults exhibited a group-level left-hand bias. Neither juvenile nor adult Macaca fascicularis exhibited manual bias at the group-level. Analysis of variance indicated statistically significant main effects of species and age class on hand preference measures. Post-hoc analysis indicated greater use of the left- versus right-hand, and greater hand preference strength independent of direction, among M. mulatta and M. nemestrina than among M. fascicularis, and among adults than among juveniles. These results indicate significant between-species variation in the development of hand preference within the genus Macaca, and are inconsistent with any one single-factor theory yet offered to explain the etiology of primate laterality. We hypothesize that the relationship between handedness and temperament that has been shown within M. mulatta may generalize across closely related primate species.