Familial influences on hand preference: genotypic variation between closely related primate species.

The emergence of hemispheric specialization has important implications for the development of higher order cognitive processes, including language and spatial skills. In this research we sought to further understand psychobiological processes associated with the development of hemispheric specialization by examining and comparing familial influences on hand preference in two closely related macaque species: rhesus macaques (Macaca mulatta) and pigtailed macaques (Macaca nemestrina). The results of our study indicate contrasting patterns of familial influence on hand preference in each species. For the rhesus macaque we found a positive correlation in the direction of hand preference between mothers and their juvenile offspring, and for the pigtailed macaque we found a negative mother-offspring correlation in the direction of hand preference. Fathers did not contribute significantly to the direction of hand preference in either species. There was a trend toward a positive correlation for strength and consistency of hand preference between parents and offspring in rhesus macaques but not in pigtailed macaques. These findings indicate that maternal influences on offspring hand preference vary between closely related primate species and lead us to question the generalizability of universal single-factor theories used to explain intergenerational transmission of hand preference in humans.