Maternal cradling bias in baboons: the first environmental factor affecting early infant handedness development?

International audience ; The most emblematic behavioral manifestation of human brain asymmetries is handedness.While the precise mechanisms behind the development of handedness are still widelydebated, empirical evidences highlight that besides genetic factors, environmental factorsmay play a crucial role. As one of these factors, maternal cradling behavior may play a key rolein the emergence of early handedness in the offspring. In the present study we followed 41Papio anubis infants living in social groups with their mother for which direction (e.g., left- orright-arm) and degree of maternal cradling-side bias were available from a previous publishedstudy. We assessed hand preferences for an unimanual grasping task at 3 developmentalstages: (A) 0-4, (B) 4-6 and (C) 9-10 months of age. We found that individual hand preferencesfor grasping exist as soon as the first months of age, with a population-level left-handednesspredominance, being stable until 6 months; to wit the period during which juveniles are mainlycarried by their mothers. More importantly, this early postnatal handedness is positively correlated with maternal cradling lateralization. Interestingly, hand preferences assessed laterin the development, once juveniles are no longer carried (i.e., from 9 to 10 months of age),are less dependent from the maternal cradling bias and less consistent with the earlierdevelopmental stages, especially in infants initially cradled on the right maternal side. Ourfindings suggest that the ontogenetic dynamics of the infant’s hand preference and its changesmight ultimately rely on the degree of infant dependence from the mother acrossdevelopment.