Bodily symmetry increases across human childhood

BackgroundAlthough bodily symmetry is widely used in studies of fitness and individual differences, little is known about how symmetry changes across development, especially in childhood.AimsTo test how, if at all, bodily symmetry changes across childhood.Study designWe measured bodily symmetry via digital images of the hands. Participants provided information on their age. We ran polynomial regression models testing for associations between age and symmetry.Subjects887 children attending a public science event aged between 4 and 15 years old.Outcome measuresMean asymmetry for the eight traits (an average of the asymmetry scores for the lengths and widths of digits 2 to 5).ResultsSymmetry increases in childhood and we found that this period of development is best described by a nonlinear function.ConclusionSymmetry may be under active control, increasing with time as the organism approaches an optimal state, prior to a subsequent decline in symmetry during senescence. The causes and consequences of this contrasting pattern of developmental improvement in symmetry and reversal in old age should be studied in more detail.