Of course, many of these “symptoms” can be triggered by other events too—a hyperventilating woman is not necessarily having an orgasm. Behold the quandary of the zoologist wishing to study orgasm in animals: while a human female can simply tell you and confirm whether or not she’s had an orgasm, a female lab rat cannot. Still, zoologists have come up with some quite convincing observations that suggest that orgasm is rife in the female animal world as well. Those same lab rats, while not amenable to filling out questionnaires, have been anesthetized and rigged with recording equipment, which, after due stimulation of their genitalia, showed something called the urethrogenital reflex: a series of rhythmic contractions of their vagina and anus, the tracings of which cannot be distinguished from those obtained from humans in the throes of orgasm. And back in 1952, intrepid researchers Noland VanDemark and Ray Hays inserted little water-filled balloons, made from the thumbs of rubber gloves, into the uteri of cows in heat and allowed a bull to copulate with them while they recorded (from a safe distance, presumably) the pressure changes inside with an ink-writing lever attached to the balloon via a thin rubber tube. Although the bull’s mount, insertion, ejaculation, withdrawal, and dismount took only five seconds, the researchers’ pressure gauge showed “tetanic contractions of the uterus” for up to two minutes after the bull had dismounted. An orgasm? A moooot point.
In female primates, which may climax in a way a bit more easily recognizable to human observers, the results are less equivocal. In 1970, anthropologist Frances Burton of the University of Toronto took it upon herself to test the then widespread idea that female orgasm was something as uniquely human as language and tool use. She put mature female rhesus macaques, belly down, on an apparatus that can only be described as a bondage table, where they were strapped in dog harnesses and wired up to monitor heart rate. It was a rather cruel setup, but the only way to keep the monkeys in a position that allowed Burton to bring them to orgasm. Surprisingly, given the less than romantic conditions, the monkeys sometimes complied. After relaxing her test animals by grooming and feeding them, Burton proceeded to subject their vaginas to regular thrusting with an artificial monkey penis. In several cases, the female would at one point start to grunt, look back at Burton, and make clutching backward movements with her arm—a behavior that primatologists had already suspected to indicate the verge of orgasm in macaques. In a few cases, Burton observed series of “intensive vaginal spasms” very similar to those known from orgasming humans.
The Scotland Yard
The reason I am going on about the female orgasm is that scientists have repeatedly suggested that it is one way in which a female mammal can influence which males’ sperm are allowed to travel up her reproductive labyrinth and which are not—a kingpin, if you will, in sexual selection in mammals. Remember that Robin Baker and Mark Bellis discovered that there was much less flowback of sperm if a woman had had an orgasm during or after her partner’s ejaculation, and that by means of her orgasm a female may be able to “select” a particular male’s sperm by giving it a push, as it were. What we did not get into is exactly how this would work. The answer, at least according to adherents of the so-called upsuck hypothesis, has to do with hydraulics.
In 1952 (clearly a golden year for low-tech veterinary reproductive experimentation), the scientist Ramsay Millar described in the Australian Veterinary Journal how he had connected (as one does) the uterus of a thoroughbred mare to a bottle of methylene blue via a copper tube and during mating saw how the uterus suddenly developed a low pressure, leading to some 80 milliliters (about 3 fluid ounces) of the blue liquid being sucked up. During the same period, other zoologists performed similar experiments on rats and mice and discovered that colored liquids, upon “manual stimulation of the vulva,” were sucked into the uterus. In the late 1960s, the obvious next step was taken: to test this in humans.
Well, rather, in a human. In 1970, Dr. C. A. Fox and colleagues of the National Institute for Medical Research in London reported how they had planted a tiny electronic pressure sensor/transmitter in the uterus of a woman—presumably Dr. Fox’s wife, Beatrice, who in the acknowledgments section of the article is thanked rather emphatically for her “help.” She then engaged in heterosexual coitus—with the article’s first author, one imagines—while the pressure changes in her uterus were recorded by a receiver placed under the mattress where the scientifically justified deed was done (twice). In both cases, the readout of the pressure gauge showed a sharp drop in pressure inside the woman’s uterus immediately after she climaxed.
If the upsuck hypothesis is correct, then by having an orgasm female mammals could give the sperm of a more stimulating male an advantage in the sweepstakes. The fact that most female humans (and monkeys) do not have an orgasm each time they copulate seems to fit this idea, as do the discoveries that certain males induce orgasm in females more easily than others. For example, in 1990 Italian primatologists Alfonso Troisi and Monica Carosi studied sexual behavior in a large group of Japanese macaques at the zoo in Rome and saw that during copulation, females would sometimes clutch and look back at the male, show muscle spasms, and “vocalize”—the same kinds of behavior that Frances Burton had seen in rhesus macaques and that seemed to be a telltale sign of the macaque climax (assuming monkey females don’t fake it). Troisi and Carosi saw this happening about 60 percent of the time when a low-ranking female was mounted by a high-ranking male, whereas in matings within the same social rank or when the female was down-dating, females would climax only once in five copulations.
The problem with such animal studies is, again, that it is hard to be sure about the females’ orgasms, short of rigging each one with a set of sensors and transmitters in their genitalia. At least in terms of certainty about what is an orgasm and what is not, it may be much more reliable to work with organisms that will simply reply when questioned about their orgasmic experiences. Such as university students. In exchange for fourteen dollars or course credits, David Puts, Lisa Welling, and their colleagues at Pennsylvania State University got seventy heterosexual student couples to have their photos taken and fill out questionnaires about the last time they had sex with each other. The women were asked (out of earshot of their partners) whether they had had an orgasm and, if so, at what point during their coitus. Then the photos of the male students were sent off to a UK university, where a jury of nine men and nine women rated their good looks on a scale of zero to seven. The results showed that women who had had sex with a male partner who (at least in the UK) was considered particularly attractive had much more often experienced an orgasm during or shortly after the male ejaculated—roughly the interval that Baker and Bellis had found was needed for more sperm uptake.
And in another study, a Portuguese-American-Scottish research team had more than 320 mostly Scottish women fill out a questionnaire on orgasm and sexual preferences. They found that the majority reported that men with a longer-than-average penis—longer than a twenty-pound banknote, the researchers had helpfully added in their questionnaire—more frequently elicited a vaginal orgasm with them.
Still, not everybody is convinced that in humans orgasm is really a way in which females exert their cryptic choice from among the males that inseminate them. In fact, there is a school of thought that doubts that the female orgasm serves any function at all. Donald Symons, author of the 1979 book The Evolution of Human Sexuality, was the first to suggest that perhaps it is just a pleasurable but functionless vestige. Not in the Freudian sense, of a dark animal past, but of the developmental program that male and female babies go through during their first few weeks in the womb.
After all, anatomically, the clitoris and the penis are so-called homologues, organs with the same basic blueprint that grow from that same genital tubercle between the embryo’s leg stumps. Not only that, but the nerves and hormones involved, yea, the whole urethrogenital reflex, which sets in motion those 0.8-second genital spasms during female as well as male orgasm, are the
same in men and women. Perhaps, says Symons, women have orgasms simply because men have them. And men have evolved orgasms because they link pleasure to ejaculation and to copulation. For men, and males in general, it pays to be on the prowl for more matings. After all, since Bateman we know that more copulations mean more offspring for males, but not for females. So an orgasm reward mechanism that makes males pursue an ever greater number of sexual encounters would instantly be spread by evolution. And the female orgasm may just be along for the ride. Just as male nipples are a pointless by-product of the evolution of the infinitely more useful female mammae and teats, the female orgasm may be a by-product of the male’s. As famed evolution writer and by-product enthusiast Stephen Jay Gould wrote in his essay “Male Nipples and Clitoral Ripples,” male nipples and female orgasms exist because “males and females are not separate entities, shaped independently by natural selection [but] are variants upon a single ground plan.” In other words, it is possible that men and women share a characteristic that has given evolutionary benefits to only one of them.
Given the evidence from uterine hydraulics in livestock, climaxing monkeys, and also tantalizing discoveries such as that the release of oxytocin during orgasm causes sperm to be transported along the uterus wall to the one ovary with a ripe follicle, I would not put much money on the by-product hypothesis. Still, the last word on this has not been said. Far from it: the by-product theory was rehashed with gusto in 2005 by Indiana University philosopher Elisabeth Lloyd—a former student of Gould’s—in her book The Case of the Female Orgasm, which has single-handedly rekindled the whole discussion on the role of the female orgasm in mammals. It has also spurred some researchers into action to obtain new data. And, frankly, this is sorely needed.
For despite all the pages devoted to the biology of the female orgasm—in the past five years alone, there have been a whopping five hundred scholarly texts on it—the hard data that we possess are very few, especially where our own species is concerned. There was only a single Mrs. Fox who ever had a pressure sensor placed in her uterus, and those two 1970s pressure tracings are all the upsuck theorists have to show for themselves. Baker and Bellis got their information on semen flowback after orgasm from just eleven women, only one of whom was responsible for two-thirds of the semen-filled condoms that they analyzed. And questionnaires, even if the whole female population of Scotland were to fill them out, can only get you so far. To really understand what role the female orgasm plays in cryptic female choice, scientists have to start studying, either in humans or in lab animals (and with a sample size larger than one!) what impact orgasm has on the chance of bringing a sperm and an egg together. As Olivia Judson, author of the inimitable Dr. Tatiana’s Sex Advice to All Creation, has written, “[I]t’s time to collect data. Without it, the debate will remain like sex sometimes is: furious, empty and anticlimactic.”
Female Larders and Fetal Loss
Every so often a story hits the headlines of a woman who impregnates herself with her ex-partner’s sperm secretly kept in the freezer, and of all the unsavory legal and moral consequences that ensue. In the animal press—the Daily Dung Fly, the Snail Mail, the Turtle Times—such stories would hardly raise an eyebrow. In fact, their readers would probably shake their heads and drily remark how typical it is for humans to make such an issue out of this. For in most animals, females routinely keep souvenirs of past mates in the form of sperm samples stored in their reproductive system. And they do so for exactly the same reason as those human women and their freezers: one day they might like to have babies from long-gone ex-boyfriends.
We all think we know that sperm cells do not live long once they have been ejaculated and have landed in a woman’s vagina. Their days in this new, feminine environment are numbered; in just three days, at the most four, they will expire, and if there is going to be any fertilizing, it has to occur before that time. But the fragile constitution of human sperm is actually an exception. In most animals, sperm inside a female can remain fresh for much longer. Bats in colder climes, for example, engage in a mating frenzy in autumn and then, sperm securely stuck against the walls of their uteruses, go happily into hibernation and only upon awakening in spring do they release the still sprightly sperm cells to produce baby bats. To some snakes and turtles, it’s no skin off their reptilian noses to store a male’s semen for several years, since suitable males are often few and far between. And in many an ant nest, the same queen rules the colony for decades, all the while fertilizing her millions of eggs with the only sperm she ever received: during her nuptial flight, right at the start of her reproductive career. Her sperm stores remain viable for all those tens of years.
So what do these female sperm larders look like, anatomically, and how do they function? There is great variation among different kinds of animals. Many snakes have deep lengthwise folds in their oviduct (the corridor leading from cloaca to ovary) where sperm are stockpiled and kept in suspended animation. Insects, on the other hand, have at the end of the vagina a central sperm chamber (often very large and convoluted) from which long tubes lead to one or more sperm pouches, where sperm can be kept until needed. In land snails, the layout is even more complex; as with many other mollusks (see Chapters 1 and 8), the sperm is delivered in a sealed package, or spermatophore, which is first taken up into the so-called sperm-receiving organ. Here, the sperm package is dissolved, and only a few sperm escape digestion and travel up the oviduct. There, they are led into one of a number of separate blind alleys, or “sperm tubules,” where they can be used at will for fertilizing eggs at any time.
Although females throughout the animal kingdom can avail themselves of such a great choice of possible types of sperm repositories, these all share one important feature: they are ultimately under female operation. Males may deliver their sperm directly into a central sperm deposition chamber, but it is the female’s muscles and nervous system that then transport them to specialized long-term storage organs, and all withdrawals of sperm savings from these larders are similarly under female control. And this sperm mobilization comes on top of the active sperm uptake that happens immediately after ejaculation, which, as we saw in the previous section, in mammals may be brought about via orgasm.
What is important to note is that there is often not just a single long-term sperm store, but many separate stashes. Many flies have two or three separate pouches in their “spermathecary”; the edible escargot Cornu aspersum has between three and nineteen separate sperm stores, and turtles have countless minuscule sperm-harboring tubes all along their oviduct. You may have already grasped the implication of this—it means that, in principle, it may be possible that a female stores sperm from each male she has mated with in its own, distinct “freezer drawer” and can summon a particular male’s sperm at will.
I say “in principle” because the evidence that this actually happens is still rather weak. The best indications of such selective sperm use by females come from a rather unlikely source: fresh cowpats in meadows. Or rather, the dung flies that call such places home.
The yellow dung fly (Scatophaga stercoraria) is a very common sight in the Northern Hemisphere, especially in pastures and meadows where cattle and sheep provide a constant supply of fresh dung. The flies themselves hardly eat the dung (they mostly feed on nectar and smaller insects), but their larvae do, which is why, to a dung fly, a fresh cowpat is one of the most romantic places imaginable. It is where they court, mate, and lay their eggs. Cruising low above the grass, the flies drop themselves to the ground as soon as their antennae register the unmistakable scent of newly produced manure, and, since they often overshoot their target, find their way to the dung on foot. Once there (or even on the way there), males seize any females they encounter and try to mate with them. They do not care too much if another male is already doing the same, so by the time a female has reached the surface of a cowpat, she is often tended by two or more males. The later-arriving males try to squeeze in under the male that has
already mounted her while he, holding on to his prize with his front legs and balancing himself on the dung surface with his hind legs, uses both his middle legs to try to kick his competitors away. Often the female is the one who suffers most during such a tussle, and many a female literally drowns in cow poo under the pressure of her many suitors. So perhaps “romantic” isn’t really the word after all.
It was an English ecologist, Geoff Parker, a former classmate of Robin “Flowback” Baker’s, who first turned these much ignored golden flies into heroes of sexual research. Completing his doctoral studies at Bristol University in the late 1960s, he realized that dung flies on cowpats were in many ways the ideal system to base one’s behavioral ecology Ph.D. on. First of all, the work was inexpensive: he needed only “a stopwatch, ruler, thermometer, tape recorder, glass vials, entomological pins, a notebook, and a pencil.” Second, the flies and their habitat were ubiquitous; doing his fieldwork meant little more than stepping into his local cattle field, gently draping an old coat side-wind to the excrement, and gathering data. The only real peril was “the occasional undetected bull,” and the only irritations “the rain and the curiosity of unhabituated cows, dogs, and small children.” So while his fellow Ph.D. students went off on costly expeditions to observe large game in Africa and came back after many months with only a few hours of observations on a single cheetah, Parker spent his summers propped on an elbow next to a cowpat quietly amassing a volume of work that has since become a classic in ecology. And in terms of the drama of the sexual behavior he observed, the flies were not outdone by big mammals. As he wryly observed, “[I]f dungflies were the size of red deer they would be the subject of a thousand books and nature films.”
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