Polygamy
Types
- Polygyny: 1-Man Many-Women
- Polyandry: 1-Woman Many-Men
Until very recently, this would result in uncertain paternity, and thus no father figure for children (terrible for society long-term).
Heavily reduces societal reproduction rate compared to both monogamy and polygyny.
It seems highly plausible that men are naturally / evolutionarily ingrained to be jealous.
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Men that do not achieve a wife that is monogamous to them seem much more likely to become violent
and/or involved in criminal activity (bad for society).
See the Religion page for how Islam attempts to handle this. - Monogamy seems to be stable for thousands of years; Plausible that this is long-term preferable compared to theoretical eugenics from polygymy.
Male Homosexuality: Proven Contributors
Fraternal birth order effect: Negative correlation between fraternal birth order and male homosexuality (i.e. for a given male, the more older brothers from the same mother that he has, the more likely he is to be homosexual)Male Homosexuality: Plausible Causes
The Gay Germ Hypothesis
See my page on The Gay Germ Hypothesis
Hyper-feminine Hypothesis
Perhaps male homosexuality is caused by a "hyper-feminine" gene or germ that creates hyper femininity in both sexes; In women, resulting in high reproduction rates, but in males results in homosexuality (low reproduction rates).
Female Bisexuality
Other
¿Is it plausible that banning homosexuality within a group (e.g. a religion, a nation, etc.) results in long-term TFR/population increases? And conversely, permitting it results in long-term decreases in TFR/population? If one were looking to create their own religion, would banning homosexuality be advantagious to the religion's spread?