Birth order and sexual orientation in a national probability sample

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Abstract
The relations between birth order and sexual orientation in both men and women were examined in a national probability sample of the United States (Laumann, Gagnon, Michael, & Michaels, 1994). In addition, a possible mechanism that may underlie a birth order/sexual orientation relationship—sibling sexual activity/influence—was examined in these data. As in previous studies, men with same‐sex attraction were born later relative to men with opposite‐sex attraction, and there was no birth effect in women. In addition, no evidence was found that sibling sexual activity/influence (e.g., mutual sexual play/activity among brothers) underlies the birth order effect in men. These results suggest that existing birth order/sexual orientation findings are reliable, despite recent sampling problems in other research areas on sexual orientation development, and that future research needs to concentrate on other theories of the birth order effect, particularly on gender‐specific (i.e., male only) developmental mechanisms.