title: The sex ratio of older siblings in non-right-handed homosexual men.
abstract: This study tested the prediction, based on prior research, that non-right-handed homosexual men will report fewer than expected older brothers. Participants were 2486 heterosexual and homosexual, right-handed and non-right-handed, male and female adults, representing five samples collected for various projects by the second author. Data on sibship composition, sexual orientation, and hand-preference were gathered in the original research using on-line (Internet) or self-administered paper-and-pencil questionnaires. The non-right-handed homosexual men reported 83 older brothers per 100 older sisters, which was significantly lower than the human sex ratio of 106 live-born males per 100 live-born females. In contrast, the right-handed homosexual men reported 125 older brothers per 100 older sisters, which was significantly higher than the expected ratio. One possible explanation of these results is that older brothers increase the odds of homosexuality in right-handed males but decrease the odds of homosexuality in non-right-handed males. A second possibility is that older brothers decrease the probability that non-right-handed homosexual males will be represented in survey research. The latter scenario could arise if the combination of some biological factor associated with older brothers and some biological factor associated with non-right-handedness is so toxic that it kills the fetus or predisposes the individual to a condition (e.g., mental retardation, major mental illness) that makes him less likely to be available for research recruitment at Gay Pride parades (etc.) than other members of the gay community.
authors.affiliation: Law and Mental Health Program, Centre for Addiction and Mental Health, College Street Site, 250 College Street, Toronto, Ontario, M5T 1R8, Canada. Ray_Blanchard@camh.net
authors.forename: Ray
authors.initials: R
authors.lastname: Blanchard
authors.forename: Richard A
authors.initials: RA
authors.lastname: Lippa
mesh_terms: D001722:Birth Order; D005260:Female; D007839:Functional Laterality; D020010:Heterosexuality / Q000706:statistics & numerical data*; D018451:Homosexuality, Male / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D009864:Ontario / Q000453:epidemiology; D015203:Reproducibility of Results; D012107:Research Design; D012744:Sex Ratio; D012801:Sibling Relations; D035781:Siblings; D012938:Social Perception