Side biases for holding and carrying infants: Reports from the past and possible lessons for today.

Most adults hold human infants on the left side, with the infant's head to the left of their own body midline. The discovery of this bias is credited to Lee Salk, who first reported it in 1960, but the same was reported at least 300 years earlier and many times again through the early decades of the twentieth century. Along with the left-side reports, however, others named the right as the preferred side. Authors on each side explained the preference and foresaw consequences for the infant: different ones in each case. This article describes the two kinds of reports, asks whether and how they might be reconciled, and discusses their possible lessons for theory and research today.