Jason G Goldman at the BBC:
Sex, we are told, is pleasurable. Yet you probably wouldn’t think that if you waded through the scientific literature. That's because most scientific accounts of sexual behaviour rest upon evolutionary explanations rather than the more immediately relevant mental and emotional experiences. To say that we have sex because it helps us to preserve our genetic legacies would be entirely accurate, but the more fleeting, experiential, pleasurable aspects of that most basic of social urges would be missing. It would be like staring at a painting with half the colour spectrum removed from it.
One thing we have been curious about, though, is whether we are the only species that experiences sexual pleasure. The question of whether non-human animals enjoy it too is a perennial – and scientifically legitimate – question to ask.
In the last 10 to 15 years, scientific evidence has begun to accumulate that animals do experience a general sensation of pleasure – as anybody who has stroked a cat will know. In 2001, for example, psychologists Jeffrey Burgdorf and Jaak Panskepp discovered that laboratory rats enjoyed being tickled, emitting a sort of chirpy laugh outside the range of human hearing. And not only that, they would actively seek out the feeling.
But does that include carnal pleasure too? One way to find out is to study instances of sex that can't possibly result in procreation – for instance, among two or more males, or females; where one or more individual is sexually immature, or sex that occurs outside of the breeding season.