Document Type

Thesis

Publication Date

1991

Disciplines

Psychology

Advisor

Jan Holtz

Abstract

In the past, several researchers have commented on a disproportionate number of brothers in the siblings of their (generally male) homosexual subjects. Conflicting data has also been presented, and the question remains unresolved. This paper explores the relationship of sexual orientation and sibling sex ratio through a meta-analysis of eighteen previously published studies from 1940 through 1982. A recent survey of adult heterosexual women provides more data, resulting in final sample sizes of 5553 homosexual male subjects, 1100 heterosexual male subjects, 445 homosexual female subjects, 436 female heterosexual subjects and 1880 male controls (sexual orientation undetermined). It was found that significantly more brothers were present in the families of both homosexual men (but not if older or single variable studies are removed) and homosexual women. The proportion of brothers in the families of heterosexual men and women did not differ significantly from the average proportion of male births in the United States. A brief summary of contemporary theories on the development of male and female homosexuality is included, as well as a review of the literature on factors affecting the human sex ratio at birth.

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