Russell: “Tan is falling into the fallacy that animals have sex for the purpose of procreation. Or of writing as if. Those bats are having sex because they’re horny, and the fellatio is somehow making their sex more satisfying. That might or might not enhance reproduction. But that is not on the little bats’ minds when they’re busy getting it on.”
Frog: “The bats aren’t making direct computations of relative reproductive success — they’re ‘feeling good’, and very often ‘feeling good’ is made better by making someone else ‘feel good’ (not assuming that the bats can actually model their partners mind like that).
Humans have sex for reproductive purposes — I would bet we’re the only ones who are that insane. Everyone else just does what they like to do.
This is like saying that animal X eats to keep their metabolism going — only a few crazy people do that. Everyone eats because they like eating.”
And of course. Animals take great pleasure from sex because it is adaptive to feel that pleasure. None of them is smart enough to understand that babies follow. And that obviates the entire discussion of what sexual behaviour counts as “natural” in humans.
The only rule we need to follow is “consenting adults”. (With the addition, of course, that if a person consents to having grievous bodily harm done to them, then this is a symptom of mental illness and places a responsibility of care, not exploitation, upon people around. But then someone who would feel inclined to exploit such a situation sexually is of course also nuts.)