OF ALL THE topics in this book, sex has the richest body of research behind it. This is because evolutionary biologists, zoologists, veterinarians, ethologists, primatologists, marine biologists, and so on (the list could go on for pages) all spend a lot of time studying how, when, and why animals have sex. Similarly, psychologists, psychiatrists, endocrinologists, gynecologists, counselors, sociologists—and, of course, ministers and bishops—all spend a lot of time thinking about how, when, and why humans have sex.
The first question you might ask is “Why do so many biologists study sex?” There are two principal reasons for this, both of which explode into myriad additional sub-reasons. First, sex is critically important to the life and survival of a species. You cannot even begin to understand how a species lives without also considering how it reproduces. In fact, this is usually where biologists start. Mating, reproduction, and all of the associated behaviors take up a pretty significant amount of all animals’ time and resources. In fact, in many species, animals spend more time in pursuit of successful reproduction than they do in pursuit of food, water, and other “material” resources. Sex is such a big part of what animals do that it should not surprise us that there is so much research about it.
The second reason that sex is such a big focus of biology is that an incredible amount of sexual diversity exists in nature. It seems no two species “do it” the same way. For example, did you know that female spotted hyenas do not really have vaginas? Instead, they have a clitoris that is so large that it is technically a phallus since they also urinate through it. To impregnate a female, the male hyena sticks his penis into the penis of the female. To top it all off, these hyena females also give birth through their penises. I probably do not need to add that hyenas are a matriarchal species in which the females dominate the males.1
There is a bewildering number of reproductive strategies out there. You name it; they do it. And I am not just talking about mechanical arrangements of intercourse. The sex act itself is just one part of the larger reproductive strategy of a species, which involves everything from mate selection and courtship to parenting and childcare. Many books have been written about the reproductive lives of various animal species, so what I have tried to do here is point out some of the complexities of animal reproduction that seem to mirror the complexities of human sexual politics. If you think we have it bad, read on.
Part of the reason that such a great diversity of sexual strategies exists is because evolution is driven by reproductive success. The way that species evolve is dictated by which members leave successful offspring. We can summarize this (or incredibly oversimplify it, depending on your perspective) by reducing natural selection in animals to three principal factors: (1) success in surviving long enough to reproduce, (2) success in finding a mate and producing offspring, and (3) the success of those offspring in having their own offspring. The latter two of these three factors are directly impacted by reproductive strategy. This is why reproduction, perhaps more than any other feature of animals, is incredibly diverse throughout the animal kingdom. For animals with closed circulatory systems, there are just a few general designs for a heart, and all animals have slight variations thereof. A heart is a heart. The same is not true for penises or vaginas. Remember the hyena? There is a boatload of diversity out there.
The word “sex” can refer to a few different things. Of course, it can refer to the act of copulation that is very recognizable in mammals, birds, reptiles, and some amphibians. It is often called “mounting,” but that is definitely not the only posture it can take. Sex can also refer to maleness or femaleness. I will discuss that use of the word and how it contrasts with gender in the next section. First, I want to talk about the basic common feature of sexual reproduction—the fusion of two gamete cells to form a zygote.
In humans and nearly all mammals, we take sexual reproduction for granted because it is all we know. There is no other form of reproduction for humans besides the sexual way. I am not saying that human reproduction requires the sexual act of copulation. That is clearly not true since the advent of artificial insemination and, more recently, in vitro fertilization. Sexual reproduction simply means the fusion of gametes—a sperm and an egg—in a process called fertilization. Whether this happens in a fallopian tube or a test tube, it is sexual reproduction because two sets of chromosomes are co-mingled, creating a distinct genetic mix.
We think of reproduction in strictly sexual terms because humans and most other mammals can only reproduce this way. However, in many other types of animals (and most plants, fungi, and protists), asexual reproduction is also possible and sometimes even the norm. Asexual reproduction can happen through some form of cloning or through parthenogenesis (the growth of an unfertilized egg into a mature adult). From insects to lizards, asexual reproduction is quite common, but very few of these species are strictly asexual. Many species can engage in either type of reproduction and will switch back and forth based on environmental conditions, time of year, population density, or some other factor.
Asexual and sexual reproduction each has its advantages. Asexual reproduction is far more efficient. For one thing, usually every member of the population can produce offspring. In a strictly sexual species like ours, only the females can reproduce. That makes the maximum growth rate twice as fast for asexual reproduction. In just a few generations, asexual reproducers can quickly overwhelm sexual reproducers. There are additional benefits in efficiency as well. For example, no time or resources are lost trying to find, attract, seduce, or capture a mate. Asexual reproducers can “do it” all by themselves. There is also no reproduction-related intraspecies competition when individuals reproduce asexually.
A common example used to demonstrate the reproductive advantage of asexual reproduction is this: if a single aphid (tiny herbivorous insect) finds herself on a rose bush in the spring, within just a couple weeks, the entire bush will be infested with aphids. Sexual reproduction, even in insects, could never give you that kind of productivity.
If sexual reproduction is so much slower and more resource-intensive, then why bother? Clearly, there must be advantages, since most vertebrate lineages have evolved to include sexual reproduction, and many, including our own, have evolved out of asexual reproduction altogether. The advantage of sexual reproduction is found in its capacity to create new genetic combinations every single generation. Sexual reproduction ensures that every individual will have novel combinations of gene alleles. Those aphids colonizing the rose bush will all be clones. On the other hand, consider yourself and your siblings. You are probably a diverse bunch, even with the limited gene pool of just your parents. That is the power of sex. By tying reproduction to genetic reshuffling, diversity is ensured over the generations. Even with only the same two parents, a couple could have trillions of children and no two would be the same genetically, save for any identical twins.
Why is genetic diversity good? At any one point in time it may not be, but over the long term, it is essential for the survival of the species. It may be true that the aphids on our rose bush are perfectly suited for their habitat and lifestyle. They may be so well adapted, so successful, that any change, however slight, would be detrimental. In that case, cloning makes really good sense, and that is why they do it. However, that will only be true for as long as the environmental conditions remain the same and resources are plentiful. By autumn, the rose bush may be dropping its leaves. Or maybe the bush gets so badly eaten that it dies and there are only grasses and sunflowers nearby—and maybe those sunflowers already have insects established there. What do the aphids do then? They must find some other way to live. They must adapt. And guess what? While aphids prefer cloning in the springtime, they inevitably switch to sexual reproduction in the autumn, which helps them prepare for new challenges, especially the harsh winter ahead.2
Adaptation can only occur if there is a wide diversity of individuals because individuals do not adapt; populations do. The species as a whole adapts through the differential survival or death of its members. If everyone is the same, everyone lives or dies the same way. If everyone is different, then there is hope that at least some members of the population can survive whatever the next challenge is. Sexual reproduction prepares a species for an unpredictable future. The environmental conditions of our world, both biotic and abiotic, are ever-changing. Even the most successful clones have a bleak future when things change in their world. This is why almost all animal species are capable of sexual reproduction, even if they do not always do it.
Sexual reproduction has evolved as the most successful means to ensure the long-term survival of the species, despite its many drawbacks. It is slower and more costly, as we said, and it also leads to the sometimes absurd phenomenon of sexual selection, where features evolve and are selected purely because they provide advantages in sexual success, not necessarily survival. For example, there is a species of Drosophila that produces sperm that is twenty times the length of its body; its testicles make up more than one-tenth of its body mass.3 That may be good for reproduction, but it does not really help with survival. We all know the obscene size of the peacock’s tail. Antlers are a rather ridiculous thing to have to lug around all year, and so on. Despite some of these evolutionary dangers, sexual reproduction has thrived on our planet because of its unique ability to provide a species with a rich genetic toolkit for surviving in a changing world. Simply put, sex is good for us.
The terms “sex” and “gender” can be confusing because they mean different things to different people in different contexts. In terms of human psychology and sociology, sex is biological and gender is a sociological construction. Gender identity is one’s understanding of one’s own sex, gender, and sexuality. Gender expression is how we live out our sex and gender in the world. This includes clothing, hair, and makeup, as well as sexuality. It is complicated, and I think it is pretty obvious that we humans have our own impressive sexual diversity.
Still, the diversity of human sexuality pales in comparison to that found in animals. When discussing animals, the terminology is a bit different, and it is currently changing as we gain more appreciation for all the complexities involved. There is but one commonality throughout the entire animal kingdom: for all species, there are only two possible gametes—a big one, called the egg, and a small one with a tail, called the sperm. Sexual reproduction occurs when new individuals are formed through the fusion of a sperm cell and an egg cell.
For animals, biological sex refers only to which gamete is made—egg (female), sperm (male), or both (hermaphrodite). Yes, hermaphrodites are very common in the animal kingdom, particularly among invertebrates. The term “gender,” on the other hand, was not used for animals until very recently. I am a fan of the definition of gender recommended by biologist Joan Roughgarden: gender refers to the particular reproductive strategy employed by an animal.4 Of course, sex is a big part of gender, but gender is more than just one’s sex, in both humans and animals. In animals, gender refers to courtship, mate selection, copulation, pair-bonding, nesting, caring for children—the whole spectrum of reproductive behaviors. We speak about animal genders when we describe their behaviors in these areas. While biological sex is usually rather simple (male, female, or hermaphrodite), gender can be complicated. In many species, there can be multiple genders within a single sex. There can be different “kinds” of females or males that are fundamentally different from each other.
This is best illustrated by example. There is a species of European wrasse in which scientists have discovered multiple male genders (but just one female gender). European wrasse are small, colorful fish that live mostly in the Mediterranean Sea. In wrasse, the different genders of males are true males—all make sperm and can sire offspring with those sperm. However, each male gender has a different strategy for “fathering” offspring. Wrasse females do absolutely no parenting of any kind. They simply squirt eggs into a nest prepared by a male and are gone forever. The males, however, spend weeks building and preparing the most elaborate and protected nest in order to entice the females to provide eggs. Then, they guard the fertilized eggs vigilantly for another week until the baby fish hatch and swim away. Right away, we can see that any preconceived notions of anthropocentric gender roles should be quickly dismissed.
However, not all male wrasse are the same. Some are the “typical” large and strong males. They do all of the work of building the nest and most of the work protecting it. They chase other males from the nest and show hostility to territory encroachment. Some males, however, are born different. They are much smaller and have nothing to do with the other males, or the females, for that matter. They do not build nests, they do not guard them, they do not protect eggs, and they do not care for young hatchlings. However, they still manage to father a fair number of offspring. They do this by being sneaky fuckers. (That is a real, if unofficial, term in evolutionary biology; I am not just being crude.) These little wrasse males have a very simple reproductive strategy. They hide in the vegetation and watch for females to deposit eggs in a nest. Then, they swim in as fast as they can and squirt their sperm before being chased out by one of the larger males. It is sneaky, but it is effective enough to father children at a respectable rate. A particularly sneaky fucker can fertilize eggs in many nests, which means his genes will mix with that of many females. It is not a bad strategy.
We are still not done with these interesting fish. It turns out that there is yet a third gender of male wrasse. These males are intermediate in size and share some markings with females. They are known as “helper” males because they offer partnership to the large males with guarding the nest both before and after the female deposits the eggs. They act as lookouts and chase away other large or small/sneaky males and possible egg predators as best they can. If the large male accepts this help and enters into the partnership, he will agree to let the helper male fertilize some of the eggs with his sperm when the eggs arrive. Then, if the deal was honored, they stand guard together for a few days. It is a model of cooperation for mutual benefit, proving that mammals do not have the monopoly on cooperation. Fish can do it, too, and not just in mindless collective schools, but as individuals.
If you are thinking that this one species of wrasse is just an aberration—a weird species that is like no other—think again. Many species of fish have two or three genders of males. In fact, one of the most abundant fish in freshwater ponds and lakes throughout North America, the bluegill sunfish, is one of the best understood of the fish with three male genders. Experienced anglers can easily tell the difference between males and females. Or so they think. Many of the fish they identify as females are actually helper males. In sunfish, the alliance-forming ritual between large and helper males is a courtship dance that includes genital contact. Quite often, when a female joins the picture to contribute the eggs, the sex is a three-way affair.
The cooperation of large and helper male sunfish provides an interesting example of same-sex parenting, but more on that later. I mention these examples here to explain how the term “gender” is used for animals. It is different than sex. Gender in animals defines the way an animal lives and behaves in ways connected to reproduction (as opposed to, say, hunting). Most fish do not copulate, at least not in the way that we think of it. Separately, the two sexes squirt their gametes into a nest. However, they do have a “sex drive” in the sense that they engage elaborate strategies that will maximize their reproductive success.
The three genders of wrasse and sunfish males explained here are not just lifestyle choices or the result of some male fish being bigger than others. Fish are born into these genders in an unambiguous way, and two of the male genders have coevolved this cooperative behavior. This is a gender, a hardwired property of the individual that determines reproductive style and capacity. Although this gender is controlled by genetics, it is manifested in behaviors. Thus, this is a good example of complex behaviors being controlled by genes and proteins. The fish do not learn these behaviors from their parents, nor is there an apprenticeship program for learning the trade. The males just know what to do based simply on their gender. The male genders are kept in balance by natural selection: if one of the partnering genders becomes too abundant, they will become less successful because they will not have partners.
Slight variations of the multiple male gender patterns are seen in many other animal species. For example, there are two genders of male red deer, one with antlers (stag) and one without (nott). One could write whole books on this phenomenon. And, in fact, many already have. (I heartily recommend Joan Roughgarden’s book Evolution’s Rainbow if you want to read more.5) The summary of this is that the particular reproductive strategy that an animal exhibits—its gender—can go much beyond its sex. And is not the same true of humans?
MUCH MORE THAN PROCREATION
The largest misconception that we must dispel about sex is that animals do it only for the conception of offspring. This incorrect notion is the biggest hindrance to understanding animal sex and, unfortunately, is the most widespread. Even many scientists who are not field biologists think this way. We will see that animals use sex for establishing and strengthening pair-bonding, for greetings to build familiarity and trust, for breaking tension and thus reducing aggression and violence, and for establishing dominance hierarchies in a social group. If you think that humans are the only animals that have sex for any reason other than procreation, think again.
Truth be told, humans do not even take the prize for the most sex-obsessed animal species—not by a long shot. Bonobos, which are among our closest relatives, are a species notorious for their constant sexual escapades.6 Quite literally, sex is like a handshake, a greeting. Sex is used to resolve disputes and conflicts and again when the conflict is over. Humans are not the only ones that enjoy makeup sex. Bonobos engage in tongue kissing, oral sex, and all manner of mutually pleasurable rubbing. None of these are procreative. They even get aroused when they find food. Often, if a group of bonobos happens upon a large new source of food, their excitement will be too much to bear, and they will engage in a hurried orgy before they dive into the food.7 The resulting sexual afterglow ensures a peaceful meal without petty squabbles over portion size.
Recent research has revealed an important qualifier for the sexual reputation of bonobos: they are much more sexually active in captivity than they are in the wild, and there may be other differences between captive and wild behaviors as well.8 However, I do not think this dooms our comparisons to human behavior by any means. We also generally have more sex when we are not busy or stressed.
There are a variety of ways to disprove the myth that animals copulate only for procreation. For example, in most species of mammal, females have a narrow fertile period in their estrus cycle that is sometimes called a heat. Only during heat will she release a mature oocyte capable of fertilization. However, this does not mean that she will only engage in sexual activity during heat, nor does it mean that males will only seek sexual activity with her during this period. Sure, in most species, females engage in more sex during heat and males are more attracted to them when they are in heat, but they still have plenty of sex outside of heat. Why would that be?
In the past, some assumed that animals were just too daft to know the difference between when they were fertile and when they were not. The claim was that the sex drive is always there, but it is just meaningless when the females are not in heat. There are two problems with this claim. First, there is no evidence for it. It may seem like a reasonable assertion, but scientific claims are not based on reason alone—they must be supported by evidence. A claim that lacks evidence is tentative, at best. Second, there are mountains of evidence for nonprocreative roles for sexual activity in all sorts of animals, some of which we will soon explore.
By the way, it has been well documented that human females have a slightly stronger sex drive during their fertile period. Another time when human females have a stronger sex drive is when they are pregnant. It does not take a biologist to guess the evolutionary benefit of that, and it most definitely is not an effort to conceive again.
Before I launch into the many functions of sexual activity in the animal kingdom, I cannot gloss over what I think is the reason why so many people, including some scientists, believe that animals have sex only to reproduce. I think it is at least partly because they are projecting their moral values onto animals and thus prejudicing their scientific opinions based on their feelings about human norms. It is a form of upside-down moral anthropomorphism. Because animals only have sex for making babies, humans should only have sex for making babies. So goes the reasoning. The problem is that it is just not true. There is way too much evidence to hold that belief anymore. You can believe what you want about when and how humans should have sex, but to believe that animals have sex only for procreation is pure fallacy.
THE PLEASURE OF SEX
As we begin, we need to keep in mind that the predisposition toward having sex, the sex drive, is hardwired in two ways. First, there is the urge itself, which requires little or no training or prior experience. In other words, there is an inborn instinct. Then, there is the pleasure-reward system. This involves the release of neurotransmitters in the brain that we experience as “pleasure.” There is a pleasure center in the brain that is sensitive to these neurotransmitters, which are released when we experience something pleasurable. Neurotransmitters hitting the pleasure center is what pleasure is. Long ago, evolution invented this technique as one way to drive animals to engage in a behavior that is beneficial for the survival of the species. Once you experience this pleasure, you will want to experience it again. It is like a drug—very much like a drug, it turns out. I am not saying that animals, especially those with much simpler brains than ours, experience pleasure the same way that we do. But they clearly have instinctual drives and urges to perform certain behaviors.
It is fair to say that the origin of the pleasurable nature of sex was probably to promote reproduction and that the “original” purpose of sex was to bring together sperm and eggs. I say it is fair, but not that it is correct, because we do not know that for sure. It does seem likely, since that aspect of sex is “older” than other functions of sex and is retained as a universal function of sex. Nevertheless, we cannot be 100 percent confident because we know very little about the behavior of ancient animal species. Behaviors do not fossilize as easily as bones do.
None of this really matters to our discussion, however. The fact that sex may have been originally for conception does not change the fact that it is now used for much more. It is like the wings of a bird. In the reptilian ancestors of birds, forelimb structures were not used for flight. Does that matter to present-day birds? Are they are using their forelimbs in an unnatural way? Of course not. Animals evolve new uses for old things. That is what we do.
In animals, the “pleasure response” evolved to promote certain behaviors (usually instinctual, but not always) by rewarding those that perform the behaviors with the sensation of pleasure. Thus, it was only natural that sex would be among the first behaviors to get the honor of being pleasurable to the animal brain. This pleasure response would have made the first animal to experience it become slightly addicted to having sex and thus leave lots of offspring that would then have the addiction, and so on. Over time, natural selection would enforce a balance between the addiction to sex and the need to do other things in order to stay alive and be successful.
However, once sex and pleasure were linked in the brain, this was a powerful tool for nature to work with by using sex for other beneficial purposes. If the brain was already wired to enjoy sex and seek it out, all that was then required was the right social setting in which other purposes of sex could then naturally emerge. Once again, it is like the front limbs of the amphibians and reptiles: once this structural scaffold was in place, the limbs could then be used for different things. In some descendants of the reptiles, the forelimbs evolved into wings. The advantage of having wings is obvious, and the developmental stages along the way from limbs to wings must have had advantages, too.
The evolution of a behavior is a little different from that of an anatomical structure, but the principle is the same. The phenomenon that sex is pleasurable was the scaffold onto which other sex-centered behaviors could emerge. If the act of sex ever became helpful for something else entirely—say, building alliances with higher-ranking members of the group—there would already be a built-in way to encourage that: pleasure. Keep this “pleasure principle” in mind as you read the pages ahead. Animals have sex because they enjoy it, and it is possible that in some cases, the pleasure is all they really “understand” about the sex that they are having—they do it because they like it. But that does not mean that it cannot also serve some other function of which they are not necessarily aware.
TRICKY USES OF SEX
Some animals use sex as a weapon! Competition for resources and reproduction is fierce, so there is great pressure to use everything in your arsenal against the competitors. For example, there is a species of garter snake in Canada that enjoys wild group sex when they emerge from hibernation in early spring. What happens is that the males tend to emerge first and then wait for the females. As each female emerges from her burrow, a group of males will surround and entangle her in a large swarm of sexual frenzy. It is a wild sex orgy, and who can even keep track of who is who?
However, some males will emerge from hibernation emitting female pheromones.9 This is sometimes called female mimicry and is the snake equivalent of Bugs Bunny putting on a wig and lipstick. What happens when one of these garter snakes emerges from the tunnels smelling all sexy and ladylike? You guessed it: the hordes of waiting males surround him and do their thing. There are no external genitalia in snakes and no sex-differential markings in this species, so the males are easily fooled. But why would he do this? What does he get out of it?
Snakes are exothermic (cold-blooded). They do not generate their own body heat; they have to get it from the environment around them. By putting himself in the middle of this orgy, a male can steal body heat from the other males. The fact that there are males waiting for him means that he was not the first to emerge and is already behind in the race to inseminate the females. He is also cold and sluggish when he emerges. What better way to warm up and get up to speed with your competition than by tricking them into putting you in the center of a giant bear hug? Once this cross-dressing snake is sufficiently warmed up, he will take his place among the other males in the competition to inseminate the emerging females.
In addition, it may also be that the female-mimicking garter snake does this in order to distract or exhaust competitors. By pretending to be a female, he tricks the other males into using up energy in a futile effort. This way, he will have an advantage over them going forward because he is fresh from hibernation and raring to go. The point here is that some male snakes clearly trick other males into having sex with them, and they gain a competitive edge when they do so.
An even trickier use of sex has been discovered in flour beetles. Beetles, like most other insects, are known to frequently engage in same-sex mounting. There are many possible reasons why this might be so. Among them, it has been suggested that a mounting male beetle may actually be depositing sperm inside the reproductive structures of another male in the hopes that the “receiver” beetle will then subsequently transfer that sperm, along with his own, when he mounts and inseminates a female. Sounds far-fetched? Sara Lewis’s research group at Tufts University found that this indeed happens. They found that males that mounted other males often ended up fathering a small but consistent portion of the offspring of females that the second male subsequently mounted.10
This is quite an effective strategy because, by mounting other males, a male can potentially spread his sperm to not only the females that he mounts, but the females that other males mount as well. Pretty sly.
Lest anyone get the impression that same-sex sexual actions have the monopoly on manipulative sex, consider sexual cannibalism. Mostly found in spiders and a few insect species, this practice involves the female consuming all or part of the male, prior to, during, or after sperm transfer.11 The cannibalism thus provides a large amount of calories and nutrients to sustain the offspring of the gruesome mating. That is all fine and good, and if that is the understood life cycle of the species, so be it. Tough luck, guys. At least you would die knowing that your children will be well provided for, which is of course the adaptive explanation of why males willingly succumb.
Not so fast. In many species, females are known to occasionally “fake it.” Either by brute aggression or by tricking a male into giving up the ghost voluntarily, some females will consume a male without laying eggs.12 Instead, she continues on her search for a “better” male, one that is not so easily caught or tricked. Harsh.
This type of trickery can even work across species. New Zealand scientists have noted the decline of the native species of praying mantis as foreign praying mantises were introduced. This is called invasiveness in ecological terminology. The invasive species of praying mantis seemed to be out-competing the native species very quickly. When scientists took a closer look, they were shocked by what they found.13 The females of the invasive species emit pheromones that strongly attract the males of the native species. Horny to the point of disorientation, the males humbly offer their lives in exchange for sex with these attractive new females. The females happily gobble them up and keep moving. The females of the new species did not bother laying eggs, which would not have been compatible with the sperm anyway. They just took the free meal and continued their invasive march.
Throughout many species, we can see sex being used for things other than simply fertilization/conception. I do not think I even need to mention that the same is true for humans. Many people use sex, especially sex appeal, to manipulate others. Have you seen a car commercial lately? Some people use sex for revenge. Others use sex to shift the power balance in an otherwise nonsexual relationship. Lots and lots of people market access to their sexuality as a commodity. Between prostitution and pornography, sex is a multibillion-dollar industry. I am not defending or promoting any of this, nor am I condemning it. All I am saying is that these sundry uses of sex are widespread and in no way to unique to human beings.
In humans, as in animals, sex is a behavior. Behaviors are just like anatomical parts: they can be utilized in a variety of ways far beyond whatever their “original purpose” may have been. Natural selection will reward creative animal species that shape their anatomy and their behaviors into new and clever purposes. At the same time, libido is a strong instinct, a behavioral drive, and this creates a potential weakness in an individual that others can exploit. Animals, including humans, will go to great lengths to satisfy their lust. It is no surprise, then, that clever animals will use the sex drive of other animals against them. Of course, humans do the same. After all, we are animals (especially when it comes to sex).
SEX AS A TRANSACTION
The discussion of prostitution, pornography, and the sex trade introduces the concept that sex can be transactional. Humans did not invent that concept. Far from it. Given the natural drive for sex, it was only a matter of time before some of our animal forebears would trade sexual access for food or other goods.
There are many species of spiders and insects in which one sex, most often the male, will present food as an offering in order to gain access for mating. Females can then be choosy about who brings the best offering.14 This has been seen in birds as well.15 Males sometimes have to “purchase” access to females or, more bluntly, to their eggs. However, researchers studying penguins in the Antarctic found that pair-bonded females will have extra-pair copulations (EPCs) in exchange for rocks, which are used to build nests.16 The point is that female penguins will trade sex for a commodity. This behavior is only typically seen when rocks are scarce, leading to an interesting headline in The Style Forum: “Even Penguins Prostitute in a Recession.”17 This behavior comes quite close to the human definition of prostitution because the sex is not part of a courtship or a pair bond, it is a quick one-time thing, and it is exchanged for a tangible resource.
In macaques, sex in exchange for grooming has been noted. Sex for meat has been observed in chimpanzees. In one very interesting example, capuchin monkeys held in an animal research facility were trained to consider small silver discs as a form of currency to purchase food or other favors from their handlers. Before long, some of the males were seen giving these token to females in exchange for sex.18 It seems that prostitution really is the oldest profession.
In humans, trading resources for sex is not always as simple as professional prostitution. How many piggish men do you know that downright expect some sexual gratification after spending lavishly on a date? I am not condoning that, but it is unfortunately very common, and I think most would agree that these men are behaving in an uncivilized—one might even say animal-like—manner.
This phenomenon has been studied on college campuses, and the results will probably depress you. In short, 27 percent of men and 14 percent of women willingly admitted that they have attempted to “purchase” sexual access to a potential partner.19 This is rarely as blunt as a direct offer of money. It is more in the realm of trying to impress with fancy gifts, expensive dinners, elaborate favors, helping with homework or studying, and so on. Perhaps more surprisingly, most individuals in this study reported that they recognized when the niceness of others was actually an attempt to purchase sexual access. Even further, at least 25 percent of the time, the solicited party honored the mutually understood arrangement and “delivered” on his or her end of the deal. At least on American college campuses, there is a vibrant economy for the sex trade.
Even more interestingly, this study revealed that the opposite transaction also occurs. Five percent of men and nine percent of women reported having attempted to give sexual access in order to get something. This is something like, “I’ll sleep with you if you do my laundry/give me your Xbox/buy me that purse.”
The point of this study was to document what we already know all too well. For humans, sex is frequently a commodity. It is often included in social and economic transactions, and some people are more effective at using it to their advantage than others.
The transactional nature of sex is not always just about sex for pleasure. Procreation can be part of the equation as well. Just like with fish and spiders, we all want to reproduce with someone who has a lot of wealth (more on this in chapter 8). The mingling of wealth and procreation is indeed something we share with animals. Just look at the various customs, now thankfully beginning to fade, surrounding the marriages of aristocrats, nobles, royals, and tycoons. One of the best ways to improve the standing of one’s family is to marry into a family of higher station. But that will cost you. After all, what are you offering to them that would entice them to “marry down?” Swirling within this retched snobbery is the bald truth that reproductive access is a tool, a bargaining chip with which to achieve social advancement.
Never is the transactional nature of reproductive access made clearer than in the phenomenon of arranged marriage. In most of the modern Western world, we react with horror at the very concept of arranged marriage. Yet, in our smugly enlightened state, we forget that for all but the last three hundred years it was almost universally practiced across the globe, and it still is in many parts of the developing world. The customs vary widely regarding who does the choosing, who has veto power, and all of that. I do not want to veer too far off the rails here, so suffice it to say that regular old autonomous marriage for love is definitely the historical anomaly for our species. For most of our civilized history (and likely much of our prehistory), we have viewed marriage and procreation through the cold hard lens of cost-benefit calculations.
The dowry is another widespread practice in which the parents of the bride bequeath a large sum of their family resources to their daughter and her new husband upon their marriage. The specifics vary, but the size of one’s dowry has historically been a very substantial aspect of a young girl’s attractiveness to potential mates. This practice was common in the ancient empires of Europe, Africa, the Americas, the Middle East, India, China, and Southeast Asia (so pretty much everywhere). The dowry has a reciprocal as well: the “bride price,” which was almost as widespread. The underlying theme of the dowry and the bride price is the concept that procreative access is a resource, a commodity, and can be purchased in, or at least associated with, economic transactions.
This brings us full circle to the earlier example of fish and spiders that must “purchase” reproductive access with food or other goods. In nature, this is called a nuptial gift, and it is quite common. It is typically a male that must provide something in exchange for access to a female’s eggs. When the nuptial gift is a food item, this is often called courtship feeding, and many spiders and insects engage in this behavior. A bird called the great grey shrike must provide a meal for a female to allow him to copulate with her. This meal is a recently killed prey animal, and size matters. Interestingly, these birds forms pair bonds, but paired males will continue to purchase sexual access from other females.20
In a rather disgusting example, male katydids actually produce a secreted gelatinous food substance and offer it to the females.21 Packed with calories and nutrients, this nuptial gift, if accepted, is traded for sexual access. It is rather like cooking a very elaborate dinner for your potential wife in order to impress her before popping the question. Except in this case, the meal is made of one’s own bodily secretions. And it gets worse. Tucked inside the meal are the sperm cells of the male. The nutrients and sustenance of the spermatophore, as this gift is called, are absorbed right into the female’s genital canal. Once the outer package of food is absorbed, the sperm cells are free to carry out their mission.22 This proposal-night dinner is more like a Trojan horse.
MASTURBATION
Many people find it surprising to discover that animals masturbate, which does not really make any sense since we have all seen a dog hump a pillow, a stuffed animal, or a leg. My guess is that our reluctance to see animals this way is rooted in the shameful way that we regard human masturbation. The reality is that masturbation has been documented in many animal species, including almost all mammals.
Some of the species in which masturbation has actually been studied include bears, walruses, lions, cows, dogs, cats, horses, donkeys, kangaroos, and even porcupines (ouch!).23 Orangutans have even been known to use toys such as makeshift dildos (to penetrate) and fleshy fruits (to be penetrated).24 Also, it turns out that just about any animal that is physically able to reach will self-stimulate orally from time to time. Animals are well known to rub against objects to obtain sexual gratification. For example, moose and caribou achieve sexual gratification by rubbing their antlers on trees.25 There is a video on YouTube of a chimpanzee using a frog to masturbate and another of a river dolphin masturbating with a dead fish.
In most species, animal masturbation leads to orgasm, although it varies widely how often it does. For example, in dogs and horses, masturbation only rarely leads to orgasm,26 while in cows and our fellow apes, it almost always does.27 Female animals do it just as much as males do, although often differently. In many mammals, females can masturbate through imitating the “male behavior” of mounting and then rubbing their genitals on whatever they are humping. Females will do this with males, other females, or even inanimate objects. Bottom line—animals masturbate in a wide variety of ways.
Why do they do it? Well, why not? As we have already discussed, evolution has linked up sexual activity to the pleasure centers of our brain as a means to encourage it. Sexual stimulation, especially climax, feels good, even if it is done all alone. For that reason, if no other, we should expect that animals are going to masturbate. And why not, if no harm is being done? As usual, nature provides a more interesting story than that. It turns out that there are several good reasons to believe that masturbation is not just neutral but is actually good for individuals and species.
The first guesses about the benefits of masturbation came from within the larger idea of “sperm competition” in many animals.28 For species in which the females mate with many males, he with the most sperm has a certain advantage when it comes to acquiring paternity. This is why, so the thinking goes, there is a rough correlation in primates between the promiscuity of the females and the size of the males’ testicles.29 From this, some have concluded that “cleaning out the pipes” would be a good idea to be sure that no old sperm were lying around. The thinking here is that routine clearing out of all of the sperm-factory plumbing raises the overall quality of the sperm count. Further, it may be beneficial to regularly clean out the tubes and glands that make the seminal fluid. It makes sense that, if you want sperm to perform at their best, the accessory juices should be as fresh as possible.
This explanation of the value of masturbation is supported by a couple of studies, including in macaques, a primate relative of ours.30 However, I am not convinced that this is a widespread function of masturbation. For one thing, does the presence of some old and slow sperm really have any negative effect on the new and fresh ones? If so, how? Also, sperm can only be made so fast. Even if it were true that masturbating every so often clears out old sperm, would there be a fine line past which masturbating too often amounts to tossing out perfectly good sperm and thus reduces the sperm count of the next ejaculate? Also, this fails to explain the masturbation of those species that do not often orgasm from it, like horses and dogs. And what about the females? This does not say anything about them.
Professor Jane Waterman published an article in 2010 detailing the masturbation habits of a species of African ground squirrel.31 She studied twenty males and found that all twenty of them masturbated regularly. They masturbated more when the females were in estrus (i.e., heat), which could be due to the sexy mood caused by all those pheromones floating around. Curiously, males tended to masturbate after sex (as opposed to instead of) and the more dominant a male was, the more he masturbated. This seems quite different from what we would expect. We usually think of masturbation as something someone does instead of sex, as a substitute when we cannot get the real thing. Not so with these squirrels—the dominant males have the most sex with the females and also do the most masturbating.
Professor Waterman hypothesized that the masturbation was a form of hygiene, a way to clean the genitals, inside and out, to prevent infections, including and especially sexually transmitted ones. Sexually transmitted infections (STIs) are a real problem for these squirrels because they reduce fertility. (They are generally not fatal because the squirrels have very short life spans anyway.) During a mating season, these squirrels enjoy one three-hour sex romp during which a typical female will mate with ten males. A nasty STI would spread through the population very quickly and potentially render them all infertile. Thus, urogenital hygiene is a serious matter—not just for the reproductive success of an individual but also for the survival of the group.
One more thing about these squirrels. In all of the 105 masturbation sessions that were observed in this study, the males consumed the ejaculate that resulted. There are two likely reasons for this. First, the mouth is used during the masturbation/grooming because of the antibacterial properties of saliva. Second, the ejaculate is consumed in order to avoid needless water loss. These squirrels are well adapted for the dry climate, and the consumption of their ejaculate seems to be part of that adaptation.
Moving on. One reason that some female mammals masturbate is because it is necessary to maintain their reproductive health. So, some females simply must masturbate. The reason is that some species have what is called induced ovulation, where an egg is not released until the female is properly stimulated. This is a very clever arrangement, especially for species that are accustomed to living in low population densities. If ovulation happens on its own schedule, an oocyte will be wasted if a male is not around to fertilize it within a day or so. While sperm can usually live for a few days in the oviducts, oocytes are much more fragile. It makes good sense for females to release the eggs only during sex. Some induced ovulators are cats, ferrets, rabbits, camels, and llamas.
In these animals, when an oocyte is ready, it can hang around inside the follicle for a little while, but it must eventually be expelled from the ovary or it could develop into a cyst. In some species, for example ferrets and cats, a ripe egg is actually painful if not ovulated within a few days. Anyone with an intact female cat can tell you that when they are in heat, it is obviously a painful experience if they do not have sex. Veterinarians and cat breeders know how to relieve this pain. There are products on the market specifically for stimulating ovulation in cats. They resemble Q-tips. So, it is not a surprise that female cats and other induced ovulators have figured out how to relieve the pain all by themselves: through masturbation.
Another idea about the value of masturbation in male animals is that it hones the sexual prowess of the animal by giving them “practice” as to how to mount and thrust properly. This is similar to the “play as practice” theory discussed in chapter 1. The idea is that, as males become sexually competent, the instincts toward humping and mounting emerge and are developed through practice.
Do any of these hypotheses apply to humans? Well, it turns out that regular ejaculation actually does improve the quality of human male sperm.32 This seems to be because the longer that fully mature sperm are held in storage, the worse they will perform when they are unleashed. This makes sense because, to conserve their energy and stamina, sperm are stored with activity inhibitors in the epididymis, a meshwork of tubes on the back of the testes. These act as sedatives to keep the sperm sleepy. Then, when the sperm are released and join with the other components of semen, they are hit with stimulators and a rush of energy sources such as fructose and citric acid. Think of the seminal fluid as Red Bull. When you look at it like that, it is not altogether surprising that the longer the sperm are held in a sedated state, the less likely they are to simply perk up and go to work when the sedatives are reversed. Essentially, this is the human version of the sperm-competition phenomenon, where the benefits of masturbation are found in the enhanced quality of the sperm.
As we attempt to discover various biological benefits of masturbation, it is important to remember that it is not important that we do not, nor do all those animals, have any realization about the benefits. From our perspective, we simply do what comes naturally, what feels good. This brings us back to the “sex feels good” phenomenon and the tendency of nature to find multiple purposes for an evolutionary innovation. As with all traits and behaviors, it is likely that there are many overlapping explanations for why animals masturbate. I suspect that each of the benefits of masturbation noted in this chapter contributes to the prevalence of masturbation in some species and contexts. I also suspect that there are additional underpinnings that we have not even guessed at yet.
However, it may be that animals and humans masturbate for no other reason than that it feels good. Biologists have never observed any harm coming to animals because of masturbation within reasonable moderation. Certainly with humans, psychologists and physicians have found no harm. In fact, there is a great deal written about the benefits of masturbation for the normal psychosexual development of teenagers.
The bottom line is that masturbation stimulates the pleasure centers of the brain that have been conveniently linked up to sexual activity. Because of that, we are driven to satisfy sexual urges and seek that kind of pleasure. Thus, masturbation would naturally have emerged no matter what. It could even be that there are no benefits whatsoever, and yet masturbation is still likely to stick around because it is very difficult to extract it from our sex lives. As long as it does no harm, there is no pressure to eliminate it, so it is just kind of “there.”
EVERYTHING IS ABOUT SEX, EXCEPT SEX
There is a saying, often attributed to Oscar Wilde: “Everything in the world is about sex, except sex. Sex is about power.” Wilde almost certainly did not say this because the use of the word “sex” to mean “sexual intercourse” did not begin until decades after his death. Nevertheless, this is a profound insight, and most psychologists will tell you that there is a complex truth behind it.
Much of what animals do revolves around sex. It occupies a great deal of their time if you consider the pains they take to get it, the time they spend doing it, the efforts they engage in to make it successful, and so on. Consider the sockeye salmon that will swim for hundreds of miles (upstream!) in order to spawn once and then die. Fish do not even get to enjoy interactive sex like we do—they just squirt their gametes. And yet, look at the lengths they go to. Look at the elaborate coloring of the golden pheasant—all of that flash and flare in order to get a mate.
For mammals, sex is much more fun, and, understandably, we spend even more time doing it and trying to do it. Even sexual activity that does not seem connected to reproduction might actually be, at least in part. For example, sex is used to establish relationships and alliances and secure one’s place in the power structure of the group. Sex is used to exert and establish dominance. Sex is used to play tricks on, distract, and exhaust competitors. Sex is used to resolve disputes and maintain group cohesion. Sex is used to strengthen pair bonds and promote good family life for raising offspring, the topic of the next chapter. All of that does have an impact on reproduction, if indirectly.
If we are talking about “sex” as everything connected to mating, reproduction, and child-rearing, then yes, just about everything an animal does is about sex. With this extended definition of sex, it turns out that the “purists” might be more correct than we originally let on. We began this chapter by saying that sex is about a lot more than just making babies. What I meant was that sex is about a lot more than conceiving babies. If we consider pair-bonding, herd cohesion and harmony, social hierarchy, or just plain having fun, the benefits and purposes of sex are built around providing for the future of the species. It is all intertwined and cannot easily be separated. When it comes to animals in the wild, it is all about sex.
The question is, are humans any different? Remember that I am not just talking about conception, and I am not even just talking about the sex act itself. For many of us, much of our lives could be summarized as making ourselves attractive to a potential mate (physically, financially, in terms of power status in the social hierarchy, and so on), searching for and selecting that mate, establishing the resources and structure to provide for the success of our children, having children, caring for those children, preparing them for their own success in this cycle, retiring from our own family building and putting resources into the success of our children’s children, and so on. These may not be our conscious motivations. Drives and urges often work subconsciously.
I am also not saying that we do not do other things along the way, but the major events and aspects of our lives involve our attempts to contribute to the next generation of our species the best that we can. Some of us are better at it than others. Others opt out of this altogether. Still, we all live in this herd together. It takes a village to raise a child, and, like it or not, we are all part of the village.
FURTHER READING
Judson, Olivia. Dr. Tatiana’s Sex Advice to All Creation: The Definitive Guide to the Evolutionary Biology of Sex. New York: Holt Paperbacks, 2003.
Roughgarden, Joan. Evolution’s Rainbow: Diversity, Gender, and Sexuality in Nature and People. Berkeley: University of California Press, 2009.