Predictions were tested using the Human Relations Area Files database that (a) homosexuality would be rarer in hunter-gatherer societies and (b) psychosocial stressors of women would predict its increased frequency. Homosexual frequency decreased as a function of amount of gathering practiced and increased with size of the local community, supporting the first prediction. Lack of control by women in sexual matters predicted increased homosexuality, supporting the second prediction. These data constitute the first quantitative cross-cultural evidence for (a) environmental mediation of homosexuality and (b) Dorner's theory that maternal stress causes homosexuality. The data suggest that homosexuality would have been rarer in our hunter-gatherer ancestors.