A new sociobiological theory of homosexuality applicable to societies with universal marriage

Several sociobiological theories have tried to explain human homosexuality. Adaptationally orthodox theories view it as a specific instance of reproductive altruism, in which the homosexual orientation in combination with a cross-gender identity is the emotional motivator of a nonreproductive role, leading to higher inclusive fitness for the individual displaying the trait in a particular environment. The nonreproduction is typically assumed to be plete—a large reproductive sacrifice. A new model is proposed in which human homosexuality remains a reproductively altruistic, trait, but in which the magnitude of the altruism is much reduced, and so presumably is more likely to result in a net increase in inclusive fitness. The theory applies to societies in which social pressures require marriage of essentially all reproductively able individuals, and does not require gender nonconformity. Hence, the new theoy fills some of the gaps left by the earlier orthodox theories, and in combination with them offers a consolidated set of hypothesis for testing.