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  • Title: Latent variable analysis indicates that seasonal anisotropy accounts for the higher prevalence of left-handedness in men.
    Author: Tran US, Stieger S, Voracek M.
    Journal: Cortex; 2014 Aug; 57():188-97. PubMed ID: 24907591.
    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.
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