Here is another angle for pure science. Say we assume that homosexual behavior is natural among the apes.
OK.
Let us also assume the average distribution of homosexuals in human populations is about 10%.
OK.
Next, say we also assume humans evolved from the apes.
OK.
If we combine all these premises, the homosexual distribution, going from apes to humans, has been on a evolutionary decline (100% to 10%).
No. No one has claimed that the "homosexual distribution" in other ape species is 100%. As in humans, it is relatively rare most of the time:
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Homosexual behavior in primates: A review of evidence and theory
International Journal of Primatology
Volume 16, Number 3, 173-204, DOI: 10.1007/BF02735477
Abstract
Homosexual behavior is defined as genital contact, genital manipulation or both between same-sex individuals. Available data indicate that this behavior is phylogenetically widespread among the anthropoid primates, but totally absent among prosimians. The majority of the 33 species that demonstrate homosexual behavior
do so rarely, but for a substantial number (N =12) it appears to be a more common pattern under free-ranging conditions. I summarize data on homosexual behavior as it relates to form, living condition, age, sex, social organization, and ecological context, and discuss hormonal, demographic, and sociosexual theories for primate homosexual behavior.
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What is interesting about this evolutionary shift into modern numbers, is that human instincts gradually evolved away from the apes. Since there is a premise that humans played a role via the suppression of behaviot, implies that changing social norms were been able to alter the ape instinct, helping to create new human instinct.
I fear you are taking your preconceptions and trying to make up science to support them. There is no scientific evidence that the incidence of homosexuality has declined as we've evolved.
The Old Testament story sort of describes the gay gangs
The Old Testament also describes a flat earth, a flood that covered the Earth to a height of 30,000 feet and a woman made out of a man's rib. It is a very, very poor source of scientific information.