Maternal cradling bias in baboons: the first environmental factor affecting early infant handedness development?
Résumé
The most emblematic behavioral manifestation of human brain asymmetries is handedness.
While the precise mechanisms behind the development of handedness are still widely
debated, empirical evidences highlight that besides genetic factors, environmental factors
may play a crucial role. As one of these factors, maternal cradling behavior may play a key role
in the emergence of early handedness in the offspring. In the present study we followed 41
Papio anubis infants living in social groups with their mother for which direction (e.g., left- or
right-arm) and degree of maternal cradling-side bias were available from a previous published
study. We assessed hand preferences for an unimanual grasping task at 3 developmental
stages: (A) 0-4, (B) 4-6 and (C) 9-10 months of age. We found that individual hand preferences
for grasping exist as soon as the first months of age, with a population-level left-handedness
predominance, being stable until 6 months; to wit the period during which juveniles are mainly
carried by their mothers. More importantly, this early postnatal handedness is positively correlated with maternal cradling lateralization. Interestingly, hand preferences assessed later
in 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 earlier
developmental stages, especially in infants initially cradled on the right maternal side. Our
findings suggest that the ontogenetic dynamics of the infant’s hand preference and its changes
might ultimately rely on the degree of infant dependence from the mother across
development.
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