The question of whether animals can be gay is one that has long fascinated and caused consternation to scientists and laypeople alike. Part of the reason for this has been borne of a desire to find parallels for human sexual behaviours and orientations in the natural world, to prove its ‘naturalness’ or the opposite.


In the past, the existence of non-exclusively ‘heterosexual’ behaviours in animals has been used to justify its existence in humans. Through a modern lens, it is clear, however, that no such justification is necessary – clearly, a behaviour doesn't have to exist in animals for it to be okay in humans! Nevertheless, the topic of same-sex behaviour in animals, and how such behaviours may have come to evolve is a fascinating one.

Why the terms ‘gay’ and ‘heterosexual’ shouldn't really be applied to animals

Despite its use in our title, terms like 'gay' or 'heterosexual’ may not be the best to use when describing sexual behaviours in animals. For one, we should be wary of over-anthropomorphising and conflating something as complex as a human sexual orientation with observed behaviours in other animals.

Additionally, in part due to a lack of concerted study in this area, such observations have always been haphazard and opportunistic. This means that they constitute merely a snapshot of what could be a vast repertoire of sexual behaviours within an animal’s lifetime, rather than something as fixed as an orientation. For these reasons, in this article I will instead refer to same-sex and different-sex behaviours as more accurate and scientific descriptors.

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Which animal species has same-sex behaviour been found in?

Despite same-sex sexual behaviours in animals often being portrayed as note-worthy or an oddity, animals have an astonishing diversity of sexual behaviours, and interactions between members of the same sex are not uncommon. Same-sex behaviours have been recorded in over 1,500 animal species across many major groups, vertebrates and invertebrates alike, from dolphins to dragonflies.

What exactly do we mean by sexual behaviour? Included in this, in addition to genital contact, are other behaviours that in a different-sex context may contribute to reproductive success, such as courtship, affection, pair bonding, and parenting. All of these have been observed between same-sex pairs.


A much-cited example is that of bonobos. Bonobos are a sister species to chimpanzees, and as such are among our closest animal relatives. They use sex in quite a different way to chimpanzees, however – sometimes described as the apes who “make love, not war”. In bonobos sexual contact, like genital rubbing, is used to greet friends, de-escalate conflicts, and cement relationships, and they seemingly do not discriminate based on sex, with female-female and male-male pairings common. Individuals do not appear to conform to a particular orientation, however. They are also promiscuous rather than monogamous, having many short-term pairings.

Check out our guide to bonobos.

Japanese macaques

This is in contrast to Japanese macaques, another primate in which same-sex sexual behaviour is commonly observed. Females of this species will routinely pair off with other females, forming temporary but exclusive sexual relationships known as ‘consortships’, which involve courtship behaviours as well as sexual contact. Females will even compete with males for same-sex partners and choose a female partner even when given a direct choice with a male alternative.

Japanese macaques / Credit: Getty Images


Same-sex sexual behaviour is very much not limited to primates. Some of the most famous examples have been found in birds. One pair of male chinstrap penguins at Central Park Zoo, Roy and Silo, became celebrities when they attempted to incubate an egg together and later successfully reared an adopted chick. Same-sex parenting has also been observed in snow geese, where females pair up to raise the offspring of both, and in black swans, in which an estimated one-quarter of all pairings are male-male.

But that's not all...

From these examples alone it is clear that same-sex behaviour is fairly common in the natural world. It is, however, also likely that it has been frequently underestimated or overlooked. Many records come from incidental observations, so it is probable that many have been missed or else left unrecorded due to being deemed as unimportant or even shameful by naturalists.

It is also likely that many incidences of same-sex behaviour have been simply miscategorised as different-sex, where scientists have viewed a sexual act and consequently made assumptions regarding the sex of the individuals. This was the case for Johnathan, the world’s oldest tortoise, who had been mating with a supposed female called Frederica for nearly 20 years before it was discovered that ‘she’ was likely a he!

Group of snow geese in elegant flight against blue sky at Bosque del Apache wildlife refuge in New Mexico in winter / Credit: Getty Images

Of course, these assumptions may go both ways, and behaviour that may be better classed as ‘affection’ may be assumed to be sexual. Social animals of many species frequently engage in what might be classed as ‘touchy-feely’ behaviours, such as hugging, mutual grooming, preening, and licking, with friendly group members of both sexes. The function of these behaviours may vary, from a kind of ‘you scratch my back and I'll scratch yours’ reciprocity, to forging and reinforcing friendly social bonds.

How do we separate intimate social interactions that may have no sexual element from same-sex sexual behaviours?

Such potentially ambiguous same-sex affection has been recently observed in humpback whales, as evidenced by a series of extraordinary images, captured by photographers Brandi Romano and Lyle Krannichfeld. The whales were first thought to be a mating different-sex pair before it was realised that both were males. These photographs appear to show the two males engaged in a copulatory-like pose, with one penis visible. This looks to be fairly clear evidence of same-sex sexual behaviours.

However, unlike as is seen in male dolphins, no copulation actually takes place, and similar petting, stroking, nose to genital contact, and full body rubbing has been seen previously in male humpback whales and been classed as affection. Perhaps the lesson to take from this is that it is very difficult to know why exactly an animal is performing a particular behaviour, and that, as ever, we should be wary of ascribing human motivations and desires to other species. Just because something would be deemed sexual in a human context, it may not necessarily be in other animals.

Why do animals engage in same-sex sexual behaviour? Is there an evolutionary explanation?

Same-sex sexual behaviour is often viewed as a ‘Darwinian paradox’ by scientists. This is because it is considered contrary to Darwin’s theory of evolution, which tells us that genes or traits that do not provide a survival or reproduction benefit should not persist. Same-sex relations are considered to be detrimental to reproductive fitness because they cannot result in offspring. Because of this, animal ‘homosexuality’ has often been ignored, or else scientists have endeavoured to find various adaptive benefits to explain its existence.

Social benefits

Some of these adaptive explanations include various hypothesised social benefits. For example, some consider the frequent male-male pairings in bottlenose dolphins (roughly half of all male sexual interactions are with other males) to be important to social bond formation and the strength of useful alliances.

Sexual competition

Other theories state that same-sex behaviours can form a part of sexual competition - by mating with another male, a male can negatively affect that male’s reproductive success.

Stress relief

Same-sex sexual contact can even help conflict avoidance through stress relief, as is seen in bonobos.

Bottlenose dolphins in Donegal, Ireland / Credit: Getty Images

Why should we care?

Contrary to this line of thought, however, more recent interpretations have questioned whether the paradox of animal ‘homosexuality’ is really a paradox at all. A review on the topic from 2019 suggest that instead of asking why same-sex sexual behaviour exists, perhaps we should be asking “why not?”. This perspective considers that indiscriminate sexual activity may have been the original ‘ancestral’ behaviour of sexually reproducing animals. Our evolutionary ancestors may have practised both same- and different-sex behaviours, and the former behaviour may have only been selected against when particularly costly. In many contexts, same-sex behaviour may, rather than being necessarily particularly beneficial, be neutral, and therefore not ‘weeded out’ by evolution.

It may even be that our historical interpretations of animal sexual behaviours have been moulded by human cultural perceptions about sexuality. Viewing same-sex behaviours as necessarily paradoxical or costly, and a divergence from a baseline ”‘heterosexuality’ may in fact stem from our own outdated attitudes. In the future, with more research, we may well come to find that animals that express a more flexible sexuality are more common than those that do not.

You can read more about these fascinating theories in this study of the evolution of same-sex sexual behaviour in animals.


Main image: Bonobo juveniles hugging each other (Pan paniscus) at the Lola Ya Bonobo Santuary, Democratic Republic of Congo / Credit: Getty Images


Leoma WilliamsAnimal behavior researcher and science writer

Leoma Williams is currently studying for a PhD at the University of Manchester, and writes periodically for both the website and print magazine