Darwin imagined sex as a relatively straightforward transaction. Males compete for females. Evolutionary success is defined by the quantity of offspring. Thus, any distractions from the business of making babiesdistractions like homosexuality, masturbation, etc.are precious wastes of fluids. You’d think by now, several hundred million years after sex began, nature would have done away with such inefficiencies, and males and females would only act to maximize rates of sexual reproduction.
But the opposite has happened. Instead of copulation becoming more functional and straightforward, it has only gotten weirder as species have evolvedmore sodomy and other frivolous pleasures that are useless for propagating the species. The more socially complex the animal, the more sexual “deviance” it exhibits. Look at primates: Compared to our closest relatives, contemporary, Westernized Homo sapiens are the staid ones.