Developmental cascades as a framework for primate handedness

Handedness as a major determinant of lateral bias in human functional cradling

Studies examining infant cradling have almost uniformly concluded with a general human left-side bias for cradling, indicating that people prefer to hold an infant to the left of their body. Explanations for the notion of the left-side cradling bias have traditionally been searched for in a variety of factors, for example, in terms of maternal heartbeat, genetic factors, in the form of an ear asymmetry where auditory information is perceived faster through the left ear, as a result of a right hemispheric functional specialization for perception of emotions and faces, and in identifying a motor bias of the infant, such as the tendency of newborn infants to lie with the face to the right when placed supine. Interestingly, handedness is generally considered an inadequate explanation for the lateralized cradling bias, despite it being an intuitively plausible one. In this brief review, I put forward the cradler's handedness as the most convincing and elegant determinant of the cradling bias. This explanation is consistent with a developmental cascades' framework where the cradling bias can be understood as the result of a multitude of factors across a range of levels and systems.