homosexuality mechanism limit population growth: evidence

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A significant volume of research has found that the more older brothers a man has from the same mother, the greater the probability he will have a homosexual orientation. Estimates indicate that there is a 33–48% increase in chances of homosexuality in a male child with each older brother, and the effect is not observed in those with older adoptive or step-brothers, indicative of a prenatal biological mechanism.

its literally a counting mechanism. basically, if a mother already produced many straight sons, theres no need for more, so gays start to be produced.