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.
Bonobos, for example, the so-called "hippie apes," are known for same-sex interactions, and for interactions between mature individuals and sub-adults or juveniles. But you don't need to be a bonobo to enjoy "non-conceptive" sex, white-faced capuchin monkeys do it too. In both species, primatologists Joseph Manson, Susan Perry, and Amy Parish, found that that females' solicitation of males was decoupled from their fertility. In other words, they had plenty of sex even when pregnancy was impossible – such as when they were already pregnant, or while lactating just following birth. In addition, interactions among mature and immature individuals were just as common as interactions between two adults, for both species.
If animals indulge in more sex than is strictly necessary for conception, that too might hint at a pleasure-driven motivation to do the deed. A female lion may mate 100 times per day over a period of about a week, and with multiple partners, each time she ovulates. It only takes one eager sperm to begin the road from conception to birth, but the lioness doesn't seem to mind. Could it be that she enjoys it? Similarly high rates of encounters have been observed among cougars and leopards, too.
Another way you might learn whether non-human animals derive pleasure is whether they have orgasms. That's especially true for females, since conception does not rely on their ability to experience one. Italian researchers Alfonso Troisi and Monica Carosi spent 238 hours watching Japanese macaques, and witnessed 240 individual copulations between males and females. In a third of those copulations, they observed what they called female orgasmic responses: "the female turns her head to look back at her partner, reaches back with one hand, and grasps the male."
While it's impossible to ask a female macaque to interrogate her feelings, it is reasonable to infer that this behaviour is similar to that experienced by human women, at least in some ways. That's in part because this macaque behaviour is sometimes accompanied by the type of physiological changes seen in humans, such as increases in heart rate and vaginal spasms. Interestingly, the female macaques were more likely to experience a response when copulating with a male who lived higher-up in their monkey dominance hierarchy, suggesting that there is a social, not just physiological, component to this, not simply a reflexive responses to sexual stimulation.
Oral sex also occurs with some frequency throughout the animal kingdom. It's been observed in primates, spotted hyenas, goats and sheep. Female cheetahs and lions lick and rub the males' genitals as a part of their courtship ritual. Oral sex is also well known among short-nosed fruit bats, for whom it is thought to prolong copulation, thereby increasing the likelihood of fertilisation.
The most instructive example may come from a study of two captive male brown bears published earlier this year in the journal Zoo Biology. Over the course of six years, researchers amassed 116 hours of behavioural observations, which included 28 acts of oral sex between the two bears, who lived together in an enclosure at a sanctuary in Croatia.
The researchers, led by Agnieszka Sergiel of the Polish Academy of Sciences Department of Wildlife Conservation, suspect that the behaviour began as a result of early deprivation of suckling behaviour, since both bears were brought to the sanctuary as orphans, before they were fully weaned from their absentee mothers. It persisted for years, even after the bears aged out of cub-hood, perhaps because it remained pleasurable and satisfying.
In most cases, researchers rely on evolutionary mechanisms to explain such animal behaviour, to resist the pull of anthropomorphosis. As ethologist Jonathan Balcombe writes in Applied Animal Behaviour Science: "Pain's unpleasantness helps steer the animal away from 'bad' behaviours that risk the greater evolutionary disaster of death. Similarly, pleasure encourages animals to behave in 'good' ways, such as feeding, mating, and…staying warm or cool."
Yet Balcombe proposes that scientists shouldn’t only view behaviour through the lens of evolution. He goes on to explain that rats prefer unfamiliar foods after three days in which they're only given a single type of food to eat. The simplest explanations for that pattern suggest that the rats' behaviour is adaptive because a diversity of foods allows them to ingest a wider range of nutrients, or maybe because it allows them to avoid overdependence on a possibly limited food source. But is that too narrow a view, when it's equally plausible that the rats just became bored with their food and wanted to try something new? To spice things up a bit? Both explanations are probably true, depending on whether you take an expansive, zoomed-out perspective, or a more immediate, zoomed-in perspective.
Likewise, sexual behaviour can be wholly enjoyable while also emerging from a deeper developmental or evolutionary origin. It is precisely because reproduction is so important to the survival of a species that evolution made it so pleasurable that animals – both human and non-human – are motivated to seek it out even when conception is undesirable or impossible. The urge to seek out that sort of pleasure, writes Balcombe, "is a combination of instinct on the one hand, and a powerful desire to attain reward on the other." If so, it's clear why these powerful feelings of pleasure aren't only restricted to us humans.