Prey or play: interactions between walruses and seabirds

Facing each other: mammal mothers and infants prefer the position favouring right hemisphere processing

The right hemisphere plays a crucial role in social processing. Human mothers show a robust left cradling/holding bias providing greater right-hemispheric involvement in the exchange of social information between mother and infant. Here, we demonstrate that a similar bias is evident in face-to-face spatial interactions in marine and terrestrial non-primate mammals. Walruses and Indian flying foxes showed a significant population-level preference for the position which facilitates the use of the left visual field in both mother and infant. This behavioural lateralization may have emerged owing to benefits conferred by the enhanced right-hemispheric social processing providing the mother and infant an optimal perception of each other.

Mother and offspring lateralized social behavior across mammalian species

Findings on nonprimate mammals place the issue of mother-infant lateralized relations in a broader context, demonstrating that humans are one of many species showing this feature. The remarkable interspecies consistency in the direction of lateralization points to a continuity between lateralized mother-infant interactions in primates and nonprimate mammals and suggests ancient evolutionary roots of human cradling bias. The results from species which, in contrast to primates, have no direct involvement of forelimbs in mother-infant spatial interactions clearly support the perceptual origin of this type of lateralization. A right hemisphere advantage for social functions relevant to mother-infant interactions is the most probable background for the left-sided biases in the behavior of mothers and infants. Recent findings suggest the contribution of lateralized mother-infant interactions to biological fitness. Mother and infant both can gain advantage from keeping the other on the left side.