Is Foot Asymmetry a Correlate of Hand Performance Asymmetry? Evidence from the Jamaican Symmetry Project

Abstract

Handedness is likely to be controlled by many genetic variants, some of which are in sex-dependent genes that also influence body asymmetry. One such asymmetry may be in foot length. Levy and Levy (Science, 200, 1291–1292, 1978) reported that right-handed males have longer right feet than left and left-handed males have longer left feet than right, while this trend was found to be reversed in females. Subsequent studies, however, were unable to replicate this effect. Here, we consider the relationship between foot asymmetry and asymmetry of hand performance in a sample of 251 children from the Jamaican rural countryside. Foot length was measured and asymmetry was calculated (L–R). An Annett peg test was used to measure speed of hand performance for right and left hands. Lateralised hand performance (LHP) was calculated by dividing the right-hand time by the left-hand time (i.e. LHP <1 = faster right hands). For boys, L–R foot length asymmetry was positively correlated to right-hand times and to LHP, and the relationships were independent of age. It is notable that the larger the relative size of the right foot, the faster the speed of the right hand, but so also the smaller the relative size of the right foot, the slower the speed of the right hand—the distribution is continuous and significant. In girls, foot length asymmetry did not correlate with hand speed. Thus, we have replicated the Levy and Levy effect in boys, but not girls. We discuss these results in relationship to the influence of sex-dependent genes and foetal sex steroids on brain and body lateralisation.