Interaction of older brothers and sex-typing in the prediction of sexual orientation in men.

Numerous studies indicate that homosexual men have, on average, more older brothers than do heterosexual men. One explanation of the "older brother" effect comes from D. J. Bem (1996), who argued that an increased number of older brothers in homosexual men can result if older brothers enhance a feminine boy's sense of being different from (and hence his attraction to) other males. Thus, he argued that an interaction between older brothers and sex-typing will occur, such that when a boy is high in femininity, number of older brothers may strongly predict a homosexual orientation; and when a boy is low in femininity, number of older brothers may not or may only weakly predict a homosexual orientation. In this study, the relations among sibling characteristics (e.g., older brothers), childhood sex-typing, and sexual orientation were examined using a database of a large sample of homosexual and heterosexual men (N > 1,000) archived at the Kinsey Institute (A. P. Bell, M. S. Weinberg, & S. K. Hammersmith, 1981a). No significant Older Brother x Sex-Typing interaction effect was observed. These results join other recent evidence that postnatal (e.g., learning/environmental) mechanisms probably do not underlie the older brother effect in men.