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by quesera
763 days ago
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Both things must be true. On the one hand, you'd expect humans (animals) to have completely bred out all forms of infertility -- except that there are non-heritable causes of infertility. (In fact, all causes of infertility must be non-heritable, or at least not inherited! :) On the other hand, it's surely true that characteristics which deprioritize or diminish the likelihood of reproduction are bred out, however incompletely. Whether it's a sense of taste that enjoys poisons, a risk-taking brain that kicks in before fertility, homosexuality (in males at least), or just not wanting children. These characteristics are bred down to a sustainable level, obviously. But they are clearly not bred out fully, nor are they consistently bred "up". |
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In many traditional societies, there is strong social pressure for marriage and children, arranged and semi-arranged marriages, etc - such that a person’s sexual orientation may not make much difference to their odds of heterosexually reproducing. Some people might enjoy heterosexual reproduction and others might endure it but they’ll do it all the same. So that would limit the selective pressure against genes that increase the likelihood of homosexuality
In the mainstream contemporary West, if heterosexual reproduction doesn’t appeal to you, then you just don’t do it-so selective pressure against those genes may exist to a degree that it formerly did not. On the other hand, the new possibilities for non-heterosexual reproduction (such as IVF, sperm/egg donation, surrogacy) might counteract that.