But establishing whether sexual pleasure ever actually tips over into orgasm is hard. Whether they regularly have them during normal copulation is much less certain; most animal sex is very brief and often quite violent. Most other vertebrates use external fertilisation; the female deposits her eggs and the male squirts them with sperm.
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Deidre Mattiske does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment. But actually all female mammals have a clitoris, the highly sensitive organ that is linked with pleasure and orgasm in women. And research is now starting to slowly unpack how the clitoris might be involved in sexual encounters in mammals. For example, a research paper presented at a biology conference this week showed that the clitoris in dolphins is very large, and more complex than we previously thought. All babies, regardless of whether they are destined to become a boy or a girl, begin development in the womb with a small bulge called a genital tubercle. Read more: What makes you a man or a woman? Geneticist Jenny Graves explains. If the developing fetus is destined to become male, the fetal testes will produce the male hormone testosterone and the genital tubercle will develop into a penis. If, on the other hand, the fetus is destined to become a female, the fetal ovary will not produce any hormones and instead the genital tubercle will develop into the clitoris. Since the penis and the clitoris both develop from the same structure, they share many similarities.
Sex, we are told, is pleasurable. 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.
Animals obviously hook up, at least during mating season. But do they like it? According to experts, there are two answers: "yes" and "it is impossible to know.