Abstract:
According to the Geschwind-Galaburda theory of cerebral lateralization, high intrauterine testosterone levels delay left brain hemisphere maturation and thus promote left handedness. Human circulating testosterone levels are higher in the male fetus and also vary with length of photoperiod. Therefore, a higher prevalence of left-handedness, coupled with seasonal anisotropy (i.e., a non-uniform distribution of handedness across birth months or seasons), may be expected among men. Prior studies yielded inconsistent evidence for seasonal anisotropy and suffered from confounding and a number of shortcomings affecting statistical power. This study examined hand preference and associations of handedness with sex, age, and season of birth in independent discovery (n = 7658) and replication (n = 5062) samples from Central Europe with latent class analysis (LCA). We found clear evidence of a surplus of left-handed men born during the period November-January, which is consistent with predictions from the Geschwind-Galaburda theory. Moreover, seasonal anisotropy fully accounted for the higher prevalence of left-handedness among men, relative to women. Implications of these findings with regard to seasonal anisotropy research and handedness assessment and classification are discussed.
Media coverage:
Results from this publication were covered in more than 120 media items from 28 countries around the world.
