This study used a recently developed statistical technique to investigate the relations between various elements of a subject’s family background and the odds of that subject reporting a sexual history indicative of a minority sexual orientation. The subjects were 78,983 men and 92,150 women who completed relevant questionnaire items in the UK Biobank, a large-scale biomedical database of volunteers aged 40–69 years. The men were divided into three sexual minority groups—homosexual, bisexual, and asexual—and a comparison group of heterosexual men. The same was done for the women. The analytic procedure consisted of logistic regressions specifically designed to disentangle the effects of birth order and family size. The results showed that older brothers increased the odds of homosexuality in both men and women, and that older sisters increased the odds in men. In contrast, neither older brothers or older sisters affected the odds of bisexuality or asexuality in men or in women. These results suggest that birth order effects may be specific to homosexuality and not common to all minority orientations. The only family size finding was the negative association between family size and the odds of asexuality in both men and women. The outcomes of this study indicate that the maternal immune hypothesis, which was advanced to explain the relation between older brothers and homosexuality in later-born males, might have to be abandoned or else expanded to explain the findings concerning females. A few such modifications are considered.

这项研究使用一种最近开发的统计技术来调查受试者家庭背景的各个要素之间的关系，以及该受试者报告表明少数族裔性取向的性史的几率。受试者是 78,983 名男性和 92,150 名女性，他们在英国生物银行中完成了相关问卷项目，英国生物银行是一个由 40-69 岁志愿者组成的大型生物医学数据库。这些男性被分为三个性少数群体——同性恋、双性恋和无性恋——以及一个异性恋男性的对照组。女性也是如此。分析过程包括专门设计用于理清出生顺序和家庭规模影响的 logistic 回归。结果显示，哥哥增加了男性和女性的同性恋几率，而姐姐增加了男性的几率。相比之下，哥哥或姐姐都不会影响男性或女性双性恋或无性恋的几率。这些结果表明，出生顺序效应可能是同性恋特有的，而不是所有少数族裔取向都共有的。唯一的家庭规模发现是家庭规模与男性和女性无性恋几率之间的负相关。这项研究的结果表明，为解释哥哥与晚生男性同性恋之间的关系而提出的母体免疫假说可能必须放弃或扩展以解释有关女性的发现。考虑了一些这样的修改。