title: Latent variable analysis indicates that seasonal anisotropy accounts for the higher prevalence of left-handedness in men.
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.
authors.affiliation: University of Vienna, School of Psychology, Vienna, Austria. Electronic address: ulrich.tran@univie.ac.at.
authors.forename: Ulrich S
authors.initials: US
authors.lastname: Tran
authors.affiliation: University of Vienna, School of Psychology, Vienna, Austria; Research Methods, Assessment, and iScience, Department of Psychology, University of Konstanz, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Stieger
authors.affiliation: University of Vienna, School of Psychology, Vienna, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Voracek
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016880:Anisotropy; D004292:Dominance, Cerebral / Q000502:physiology*; D005060:Europe; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D012621:Seasons; D012737:Sex Factors; D013739:Testosterone / Q000378:metabolism*; D055815:Young Adult
chemical_list: D013739:Testosterone
keywords: Handedness; Latent class analysis; Laterality; Seasonal anisotropy; Seasonal variation