Sex ratio of older siblings in heterosexual and homosexual, right-handed and non-right-handed men.
Level 4 - case-series / case-control
Pooled retrospective case-control and cross-sectional comparative study.
PubMed 17186124 · doi:10.1007/s10508-006-9119-2
What was done
Data from previous studies were pooled to examine the sex ratio of older siblings across four groups of men defined by sexual orientation and handedness (N = 8,201). The observed ratio of older brothers to older sisters in each group was compared against the expected human secondary sex ratio of 106 males per 100 females.
What was found
The observed ratio of older brothers to older sisters was 105 for heterosexual right-handers, 128 for homosexual right-handers, 127 for heterosexual non-right-handers, and 96 for homosexual non-right-handers. The ratios for homosexual right-handers and heterosexual non-right-handers differed significantly from the expected value of 106.
Why it matters
The findings indicate that the interaction between handedness, fraternal birth order, and male sexual orientation involves atypical older sibling sex ratios in both heterosexual and homosexual non-right-handed populations.
Limits
The study is an observational analysis based on aggregated secondary data from previous studies, carrying potential selection bias and heterogeneity across pooled samples. Specific recruitment criteria and measures of handedness are not detailed in the abstract.
Cited by
- supports Gay men have an older brother to older sister ratio of roughly 140 to 100, compared to approximately 105 to 100 in heterosexual men.