Birth order and sibling sex ratio in homosexual transsexual South Korean men: Effects of the male-preference stopping rule.

Two biodemographic variables - birth order and sibling sex ratio - have been examined in several Western samples of homosexual transsexual men. The results have consistently shown that homosexual transsexuals have a later birth order and come from sibships with an excess of brothers to sisters; the excess of brothers has been largely driven by the number of older brothers and hence has been termed the fraternal birth order effect. In the present study the birth order and sibling sex ratio were examined in an Asian sample of 43 homosexual transsexual men and 49 heterosexual control men from South Korea. Although the transsexual men had a significantly late birth order, so did the control men. Unlike Western samples, the Korean transsexuals had a significant excess of sisters, not brothers, as did the control men, and this was largely accounted for by older sisters. It is concluded that a male-preference stopping rule governing parental reproductive behavior had a strong impact on these two biodemographic variables. Future studies that examine birth order and sibling sex ratio in non-Western samples of transsexuals need to be vigilant for the influential role of stopping rules, including the one identified in the present study.