In this issue Majnemer and Barr (p 370) bring to our attention two groups of 4 and 6-month-old infants, who had spent much of their time supine. As the authors describe some aspects of their immediate early development, I find myself being repeatedly reminded of other associated and longer-term aspects of position-related development. In their discussion the authors rightly remind us that ‘infant motor development involves a dynamic interplay between intrinsic maturation of the musculoskeletal and nervous systems and extrinsic experiences’. But what about genetic bias?