Masturbation in Animals - All You Ever Wanted to Know

For those who want a quick summary: A. Yes, masturbation definitely exists in animals, both males and females, especially among mammals. B. There are many evolutionary speculations about the benefits of masturbation, but nothing is definitively known.

Now, in detail:

1. The Social Context of Research on Animal Masturbation

The field of sexuality, as is well-known, deals with stigmas and social norms that hinder research. Indeed, researchers omitted reports of observations of animal masturbation because it seemed immoral to them! (Similarly, they omitted reports on homosexual behavior in animals).

Farmers even went so far as to punish animals when they saw them masturbating! In some cases, they created cruel devices to prevent animals from masturbating. For instance, they placed a device on the penis of breeding stallions that caused pain and physically prevented erection when the horse was not 'on duty'.

Additionally, when researchers, who viewed masturbation as improper, saw and reported animals masturbating, they interpreted it as unnatural behavior due to the animals being in captivity. However, many observations of animals masturbating in the wild have since accumulated, leading to the conclusion that masturbation is in fact a natural behavior in nature.

2. Which Animals Have Been Observed Masturbating in the Wild?

In the scientific literature, I have encountered documentation of masturbation in the following animal species (males and females): cats, dogs, bats, bears, weasels, squirrels, bulls, goats, sheep, zebras, horses, deer, camels, elephants, penguins, whales, dolphins, porcupines, birds, lions, and 35 types of monkeys. Surprisingly, even turtles, marine iguanas, and snakes have been observed masturbating! On the other hand, there are also monkeys (New World monkeys) that have been studied and found not to exhibit masturbation behavior. So, it may be that not all animals masturbate, but masturbation is a common phenomenon in wild animals.

3. So There is Masturbation in Nature, But How?

The technique of masturbation varies among animals according to their physical capabilities: horses rub their penis against their belly, deer use their antlers (!), lions use their front legs, walrus use their fins, and primates (monkeys) mostly use their hands, but baboons use their tails and sometimes even their nipples. lastly, there are dolphins that abuse other animals for masturbation (!).

Do you know the joke about why dogs perform oral sex on themselves with the answer being because they can? Well, indeed, chimpanzees, baboons, and some other types of monkeys, as well as squirrels, goats, sheep, foxes, and other animals can reach themselves orally and do so. In some primates, females have also been observed using improvised toys (sticks, pebbles, and leaves), and there are other female animals (that are not primates) that have been observed using objects from their environment to rub their clitoris: porcupines, rodents (like mice and rats), birds, and whales.

4. The Clitoris in Animals

For those surprised that not only women have a clitoris, yes, in all mammals (and not just mammals) females have a clitoris, and they definitely use it. For those wondering which female animals that are not mammals have a clitoris, here's what I found: among birds - ostriches and ducks, among reptiles - some snakes and lizards, among fish - mantas and sharks, and finally among invertebrates - octopuses and squids have a clitoris-like structure. However, most reports of masturbation in females come from primates, probably because in primates (as well as in mice and rats) the external clitoris - the part of the clitoris visible to the eye - is far from the vagina and it is easy to identify masturbation with it. In other species, the clitoris is inside the vagina (for example in dogs and in rabbits) or at the edge of the vaginal opening (for example in horses, pigs, and cats), making it harder to see.

By the way, it often seems that the clitoris is viewed as an evolutionary remnant that women have from the male penis, meaning the existence of the clitoris is a biological result of the existence of the penis. However, in ostriches, for example, the female has a clitoris but the male - like most birds - does not have a penis. To summarize: the clitoris isn't a female byproduct of male having a penis.

More posts in my blog

5. Masturbation in Females vs. Males

In general, it is more difficult to determine whether females are masturbating or, for example, if they have an itch on their clitoris. The reason is that in males, the result is more visible: erection/ejaculation. Thus, when a female monkey was observed inserting a pebble or stick into her genital area, the initial explanation was that she was experiencing an itch, but upon examination, no cause for the itch was found. Other indicators that led researchers to conclude that the behavior in females is masturbation include: chimpanzees were observed laughing while touching their genital area, and in other cases, researchers noted facial expressions that were clearly orgasmic, etc. But without a doubt, it is easier to determine masturbation in males.

Perhaps because researchers are less certain when it comes to determine masturbation in females, there are fewer reports of masturbation in the wild among females compared to males. On the other hand, this is also the case with humans, with whom we can communicate and ask: In representative surveys of the population, when asked if they had ever masturbated in their life, 95% of men said yes compared to about 70% of women, and almost twice as many men reported masturbating in the last month compared to women. This gender gap may reflect social norms that historically viewed masturbation as a sin and unhealthy behavior in general, but especially for women. People even believed that masturbation caused mental illness specifically in women. (Conversely, for a long period and up to about 200 years ago, it was thought that female 'hysteria' was caused by the inability to achieve sexual satisfaction in intercourse, and the cure was to achieve it through masturbation of through the Doctor help! yup).

In conclusion, masturbation exists in nature in both males and females. It is difficult to say today whether the reason it is more common among men compared to women is social, and if the reason for more reports in male animals compared to females is a technical result of the ease of defining masturbation in males compared to females, and also due to the greater discomfort of researchers discussing female compared to male masturbation.

6. Why Masturbate?

From an evolutionary perspective, masturbation seems like a waste of resources without any benefit. No wonder that even when it became clear that animals masturbate in the wild, the prevailing opinion was that it is behavior that exists only when animals have no opportunity to mate. That is, masturbation seemed like a release of sexual drive aimed at mating when there is no ability to achieve mating. However, field findings contradicted this as well: animals were observed masturbating even when there were potential partners around them.

So if not for release, perhaps the simplest answer is also the correct one - it's fun. That is, animals masturbate because they enjoy it. But the question is why animals are built in such a way that masturbation is enjoyable. If there were an individual for whom masturbation is not enjoyable but mating is, he saves resources without his reproductive ability being affected, and in the end, he has an advantage. As I mentioned earlier, New World monkeys have been extensively studied, and no reports of masturbation have been observed in them. This indicates that masturbation is not an inevitable byproduct of sexuality.

7. Explanations for Males

Among primates, those that live in groups of several males and several females together were found to masturbate more than primates that live alone. Interestingly, in those animals the rate of mating is higher compared to primates that live alone. This surprised researchers for a reason I'm going to explain after a short background: In such groups, where several males and several females mate with each other, there is usually competition among the males for mating. Often a hierarchy is formed where the dominant male mates more than the others or mainly he mates when the females ovulate. That is, in animals that live in a sexually non-monogamous group, with several males and several females, there is competition for access to females. Besides the competition for access to females, there is usually another competition among the males: sperm competition! In such species, males produce particularly large amounts of sperm to flush out the previous male's sperm and to increase their chances of fertilization. (What do I mean in large amounts of sperm? well, in pigs, I'm talking about half a liter sperm!).

Because of sperm competition researchers were surprised finding out that animals living in a non-monogamous group masturbate more than animals that live alone: masturbation is expected to reduce the amount of sperm and harm sperm competition! So how is it that in such groups there is more male masturbation?

We can think of several explanations, but before that, it's important for me to note that this post is now moving from facts to mostly educated-speculations or hypotheses. Hypotheses have their place; they require creativity and knowledge, but as long as they are not proven, they are stories, even if they are the best stories we have.

7.1 Improving Sperm Quality

Masturbation might help males get rid of old sperm, which is more likely to be less viable than fresh sperm. If they don't get rid of the old sperm and fertilization occurs with one of those old sperms, there's a higher chance that the fertilization won't lead to a healthy offspring. Essentially, if they don't masturbate, they're shooting themselves in the foot. Indeed, sperm quality in Japanese macaques was measured, and it was found that the longer the time since the previous ejaculation, the lower the sperm quality. However, it's still not certain that this is the explanation because males in non-monogamous groups of several males and females, who mate more frequently than those living alone, already have less old sperm. Additionally, males living alone and masturbating less still 'want' to successfully fertilize when they finally mate. So we would expect them to masturbate even more than those living in groups! Finally, as is well-known, humans also masturbate, even though sperm competition didn't play a significant role in human evolution (this is known from the relative size of human testicles compared to other primates). Today, humans usually live in societies where one man has several women or in monogamous societies. Such a man has many opportunities to ejaculate during intercourse and doesn't need to get rid of old sperm. The existence of matrilineal tribes raises the possibility that in the past, the social structure of humans was different, and then masturbation might have indeed improved sperm quality. I will write about matrilineal tribes another time.

7.2 Protection from Diseases

This explanation was proposed for animals that masturbate after mating, such as the African ground squirrel. It lives in a non-monogamous group of several males and several females and masturbates mainly after mating. The squirrels that mate more also masturbate more. It might be that in animals like the African squirrel, masturbation after mating serves to clean the sperm duct from pathogens. This is a possible explanation only in animals that masturbate after mating until ejaculation, and as is known, this is not always the case.

7.3 Anxiety Reduction

In rhesus monkeys, the opposite is found: they masturbate just before mating and do not reach ejaculation. This led to two possible explanations for the evolutionary importance of masturbation, and the first is anxiety reduction. In nature, animals are afraid to approach each other, and the sexual context can increase anxiety even more. Studies in rats have indeed shown that mating is anxiolytic, but I am not aware of any study that directly tested this hypothesis on masturbation. In any case, the next possibility is even more intriguing:

7.4 Getting Aroused and Ready to Ejaculate

These rhesus monkeys live in a non-monogamous group of several males and several females together, and there is a hierarchy among the males. If a high-ranking male notices a lower-ranking male mating, he immediately drives the lower-ranking male away. Since their mating duration is long (it can last about an hour), this gives the high-ranking male enough time to notice the event and end it. It could be that the lower-ranking males responded to this by shortening their mating duration: they masturbate beforehand, thus shortening the time to ejaculation during mating and managing to ejaculate before being driven away. According to this explanation, lower-ranking males masturbate more, but it is still unclear if this is indeed the case.

7.4.1 Evolutionary Battle and Implications

It's interesting to think about the last explanation from the females' perspective: they are interested in competition among males so that fertilization will be from the highest quality male. Female cats meow loudly to attract all males to compete when they ovulate. In primates, it's thought that females vocalize close to orgasm for the same reason: to encourage competition. For females, fertilization by a lower-ranking male is a mistake. Therefore, the evolutionary response of females to the masturbation-to-ejaculate-quickly strategy of low-ranking-males could be having longer mating before orgasm to allow the high-ranking male enough time to drive away the lower-ranking male and to reduce the chances of fertilization from such males. As I will soon elaborate, it seems that the orgasm in females aids fertilization. Therefore, lower-ranking males who have adapted to quick ejaculation through pre-mating masturbation fail to bring the female to orgasm, reducing the chances of fertilization from them.

If such behavior existed in humans as well, it could explain the well-known orgasm gap: women find it harder to reach orgasm than men, and it takes them, on average, longer.

8. Female Masturbation

Until now, I have discussed ideas that try to explain male masturbation. Now, let's explore explanations for female masturbation. Unfortunately, as in many areas, there is less knowledge on the female side, which is a pity.

8.1 Learning How to Achieve Orgasm

As mentioned, it is believed that female orgasm aids fertilization. But wait, do animals even experience orgasms? The answer is that we can't know for sure. Even among humans, we can't truly know others' experiences. We can measure physical changes like breathing rate, vaginal and rectal contractions, but orgasm is more than that: it's a bodily and perceptual experience. We can measure the physical part, but the perceptual part is problematic. (The relationship between bodily and perceptual experience is even more complicated because sometimes women experience orgasm without vaginal contractions, or vice versa - there are contractions without the perception of orgasm). While we can talk to humans and get descriptions of the experience, even humans struggle to describe what they feel during an orgasm - "It's indescribable" is a common phrase. In one study, out of ~40 women they received ~70 types of orgasms by verbal description of the experience.

Returning to animals, we can see that mating is enjoyable for at least some animals - both males and females - and there is support for the idea that even rats experience something akin to orgasm, not to mention the primates previously mentioned. In any case, in this post, female orgasm in animals refers to a series of vaginal contractions without considering the perceptual experience.

Why are these contractions necessary during orgasm? The common explanation is that in animals with internal fertilization, the sperm is deposited in the vagina and needs to reach the uterus and then the location where it will meet the egg. The claim is that the contractions push the sperm up the vagina towards the cervix and into the uterus itself, a concept known as insuck or upsuck. This idea was tested experimentally (here) and indeed vaginal contractions can pull the sperm into the uterus. This could explain why female orgasm improves the chances of fertilization and I think that even more importantly it gives females some influence over the chances of fertilization even if unintentionally, as previously mentioned (Section 6.4.1). This last point is important as it gives the female some choice from whom she would become pregnant. Most authors focus on the fertilization itself but for females in nature it's usually relatively easy to reach their full reproductive potential and it's most important for them to choose. This is especially true among mammals in which the mother's investment in the offspring is high. Another possibility, which also gives female orgasm a role in fertilization, is that vaginal contractions encourage the male to reach orgasm, thus again the female influences the likelihood that mating will lead to fertilization. My point is that orgasm was selected in evolution as a way for females to choose with whom to mix their genes by enhancing the chances for fertilization

In any case, given the idea that orgasm aids fertilization, the theory is that masturbation teaches the female how to achieve orgasm, thus giving masturbation a role.

8.2 Cleaning the Vagina

Another explanation for female masturbation suggests that the lubrication produced during masturbation cleans the vagina of old sperm and various other substances that shouldn't be there. Therefore, masturbation has a health role and may also support fertilization when mating occurs.

8.3 Creating Competition Among Males

In some animal species, pheromones produced in the uterus lining attract males. Pheromones are substances that, like scents, evaporate into the air, are detected by other animals, and alter their behavior. Masturbation causes more pheromone secretion, thus males in the vicinity who smell the pheromone change their behavioral priorities and will make every effort to reach and mate with the female. Not only do pheromones attract males, but also the sight and sound of the masturbating female: in orangutans, when a young female wants to attract a male, she starts masturbating in front of him (younger females are less desired by the males).

8.4 Stress Relief

As already mentioned regarding males, sex can be a source of stress, especially in nature. Females for whom sexual arousal reduced stress felt more comfortable approaching males and eventually mating with them and gave them an evolutionary advantage upon females that for them sex didn't reduce anxiety. Later on, females utilized masturbation to reduce stress in a non-mating context. Hormonally, orgasm causes the brain to release a hormone called oxytocin into the blood, which causes contractions in the vagina, uterus, and rectum, and in males, contractions in the sperm duct. This same oxytocin also inhibits the action of another hormone - cortisol - a hormone that causes the sensation of stress. This support the view that masturbation could reduce stress.

Conclusion

Researchers in the field currently conclude that animals masturbate because they enjoy it, (da..) and there are various hypotheses about how masturbation helps genes get passed on. That is, why evolution retained a behavior that is enjoyable but seemingly involves a waste of resources without reproductive 'profit'. Some explanations have factual support, and there may be several 'correct' explanations for a particular species, while different species of animals might have entirely different reasons.

In any case, masturbation exists in the animal world and is even common. It's time for the study of sexual behavior to no longer be considered esoteric or even disreputable research. We want to know because we are curious, to know for the sake of knowing, to understand the world.

I work hard to make high-quality, in-depth, and FREE content on the science of sexuality accessible. If you'd like to support me with a coffee (4$), I'd greatly appreciate it, and it would help me continue. Thank you in advance!

Buy me a coffee?

Credits Most of this post is written after the following article: Masturbation in the Animal Kingdom, Journal of Sex Research, (2023) by Lateefah Roth, Peer Briken, and Johannes Fuss.

The cover photo shows a Vervet Monkey (an Old World monkey) and it was taken by Bernard Dupont, France, who posted it on Flicker. .