[Pseudoscience-is-malarkey (OP)]

It is a scientific fact that dolphins have sex for pleasure. Is there hard evidence that they're not the only non-human animal that partakes in carnal desires? What motivates animals to do the deed if there is no pleasure/relief factor?

[Kryptid]

Dopamine has been detected in the brains of mice when they mate, so surely they get something out of it. Of course, humans, dolphins and mice are all mammals. Other types of animals may feel something different. Once you start getting on the level of worms, perhaps it's all just a matter of simple genetic programming rather than satisfying urges.

[alancalverd]

You may need to separate the  neural pleasures of copulation from the hormonal  drive to discharge ova or semen. Whilst  humans are pretty shallow in their mating behavior, whatever drives and facilitates salmon and eels to swim a couple of thousand miles back to their birthplace, deposit and fertilise eggs, then die, is something of a deep mystery. More so with eels and barramundi, which change sex (not behavioral gender, actual cellular sex) as they age.