Jones M B, Blanchard R
Department of Behavioral Science, Pennsylvania State University College of Medicine, Hershey 17033, USA.
Hum Biol. 1998 Aug;70(4):775-87.
Homosexual men tend to be later-born children. Slater's index, the ratio of older sibs to all sibs, is consistently higher for male homosexuals than for comparable heterosexuals. According to some explanations of this tendency, homosexual men are later born with respect to their brothers and later born with respect to their sisters only secondarily and less strongly. We show that if sisters have no direct bearing on a brother's sexual orientation and brothers do, then [formula: see text] On the other hand, if sisters have the same bearing on a brother's sexual orientation as male sibs do, then [formula: see text] These ratios are calculated and compared in nine samples of homosexual men and nine corresponding samples of control heterosexuals. The first equation holds for homosexual men, and the second equation holds for heterosexual men. The late birth order of homosexual men is sex specific. What matters is a boy's birth order relative to his brothers only. This effect may have its origins in an immune reaction or in behavioral contagion.
同性恋男性往往是晚出生的孩子。斯莱特指数，即哥哥姐姐数量与所有兄弟姐妹数量的比率，男性同性恋者的该指数始终高于可比的异性恋者。根据对这种倾向的一些解释，同性恋男性相对于他们的兄弟是晚出生的，而相对于他们的姐妹只是次要且较弱程度上的晚出生。我们表明，如果姐妹对兄弟的性取向没有直接影响而兄弟有，那么[公式：见原文]。另一方面，如果姐妹对兄弟性取向的影响与男性兄弟姐妹相同，那么[公式：见原文]。在九个同性恋男性样本和九个相应的对照异性恋样本中计算并比较了这些比率。第一个等式适用于同性恋男性，第二个等式适用于异性恋男性。同性恋男性的晚出生顺序具有性别特异性。重要的只是一个男孩相对于他兄弟的出生顺序。这种影响可能源于免疫反应或行为传染。
