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The Case of the Female Orgasm : Bias in the Science of Evolution

by Elisabeth A. Lloyd






at George Mason University



Come Again?
11:14, June 10 2005
The science behind female orgasm

Female orgasm is hot these days—with a spate of recent stories covering research on its genetic components and examining a new book on a theory about its evolution. But most of the coverage missed the chance to help readers and viewers truly understand the science and the debate.

The theory, supported by biologist Elisabeth Lloyd in The Case of the Female Orgasm, was covered by the
New York Times and New Scientist and soon picked up by numerous other publications and media. It holds that female orgasm serves no evolutionary purpose and is merely a happy byproduct of the fact that males and females have a similar body plan. This fits well with women’s preference for clitoral as opposed to vaginal stimulation: the clitoris is the anatomical analog of the penis, and has similarly intense neural connections to the brain, unlike the vagina.

The new genetic study, published in Biology Letters, shows that identical female twins are more likely to be similar in their rates of achieving orgasm than fraternal twins are, whether during intercourse or masturbation. Such studies are used to tease out the genetic components of various behaviors: if identical twins are more alike than fraternal twins, genes probably play a role because identical twins share the same genes, while fraternal twins are no more alike than other siblings and so share only about half of their genes.

The finding suggests that there are genetic reasons for at least part of the variation in women’s ability to reach climax, which could undermine the idea that female orgasm has no purpose. Genetic variations are the basis for natural selection: if a characteristic is not influenced by genetics, biological evolution cannot act on it. In order for a characteristic to be subject to evolution, it has to be both genetically influenced and varied— and some variants have to provide greater survival value than others.

So does this mean Lloyd’s theory is kaput? No. In fact, Lloyd told New Scientist that the genetic variation supports her hypothesis that female orgasm is useless. She claimed that the variant which makes orgasm difficult to achieve during vaginal intercourse is so common that if orgasm were important for procreation, those with the gene for difficult climax would have been weeded out by selection.

However, this might not be the whole story either. It may be that, as the authors of the twin study told UPI, the very elusiveness of female orgasm is what confers a survival advantage. A skilled lover may produce higher quality offspring. Or, the difficulty of pleasing a woman may actually bind couples together: research finds that “intermittent reinforcement” in which rewards only occur infrequently is actually more addictive than pleasure which is easily predictable. Further, genes which offer a disadvantage in one way often offer an advantage in another—the classic example of this is the gene for sickle cell anemia. One copy protects against malaria without causing illness; two copies offer malaria protection but lead to sickle cell disease. Female orgasm may matter, but other factors may be even more critical to survival and/or reproduction—leading to genes which get in the way of orgasm being preserved.

It’s also important to note what most of the coverage on the subject missed: our whole biological make-up is determined by our genes. The environment affects the expression of those genes, but the fact that orgasm ability varies with biology should be no more surprising than the idea that eyesight or pain sensitivity has genetic components. The fact that genes influence female orgasm rates isn’t really news. The discovery of the gene or genes in question, however, really would be: they would be prime targets for pharmaceutical companies looking for a female counterpart to Viagra.




Elisabeth Lloyd's views on the new heritability study of female orgasm

June 9, 2005

I’m interested in discussing the implications of the new heritability study on female orgasm for theories of the evolution of the trait. Tim Spector and his colleagues investigated 4,037 women, and established a heritability of .34 for orgasm with intercourse, and .45 for orgasm from masturbation, as reported in Biology Letters.
I’ve been consulting on reports on this particular paper for Science and New Scientist [] over the past 10 days, and I’ve examined the detailed experimental results. It’s a well-designed study with a very large sample. Their sex questionnaire seems to have been well-conceived, and I believe that their survey results are as accurate as any I've seen. There are several reasons to believe that they’ve managed to avoid some common problems with orgasm surveys (see the paper). Their heritability numbers are within the standard range of complex multigenic physiological traits.
FIRST CONCLUSION: The heritability part of the study seems to me to be methodologically standard, with the bonus of a very large sample. It's results are in line with the results of the Australian study of Dawood et al. of 3000 women. The sex survey part of the study is well-designed, the survey results are in line with standard results, and the heritability ranges are in line with other complex multigenic physiological traits. It looks like standard-to-good science to me, modulo the problems with human heritability studies. The paper calls attention to evolutionary questions, but draws no conclusions along these lines.
Spector and his colleagues may not draw any evolutionary conclusions in the actual paper, but in the BBC and in the Guardian,12996,1501314,00.html, Spector is reported as making a serious scientific blunder. Here is a passage from the Guardian, which is apparently a paraphrase from Spector: “The genetic control over how easily women experience an orgasm during sex shows it is subject to evolutionary pressure, which means it must confer a biological advantage.”
But this is just a mistake.
A genetic basis to the trait shows no such thing. It shows that the trait is a *candidate* for natural selection, but it also equally well could have arisen as an embryological byproduct of selection on the male orgasm, much as the male nipple arose as a byproduct of selection on the female nipple. Under the byproduct view, the trait of female orgasm has to have a genetic basis. Why? Because the trait is hypothesized to be the same trait that is strongly selected in males, and basically developmentally “slopped over” in females.
The fact of a newly documented genetic basis alone weighs neither for nor against there being an adaptive evolutionary account of female orgasm. Both the adaptive and the byproduct accounts require that the trait have a biological basis.
In the newspapers and in the paper itself, Spector mentions several potential adaptive theories; I have carefully examined evidence for each of these in my book, “The Case of the Female Orgasm,” and found serious problems. Most importantly, when Spector promotes his favorite adaptive explanation for female orgasm, he is flying free of his own data – not only does he not have any evidence to support it, his own data actually tell *against* this favored theory. For some reason, he misrepresents his data documenting variability as supporting his favored theory, and has failed to comprehend the most basic evolutionary logic of his own proposal.
As the Guardian article makes clear, Spector is (re-)proposing a theory that orgasm is a mate-selecting device; he claims that the fact that orgasm during intercourse is difficult to attain is an evolutionary adaptation itself, making the well-known variability in orgasm among women an adaptation.
But we run into trouble immediately. The proposed adaptive state is a conditional response to quality males – have an orgasm if he’s a good guy, don’t if he’s not – and under this theory, clearly the population of women was under selection pressure to have moved towards that optimum peak (balanced by the usual energetic costs, and so on). So why would that be an argument for the *variability* of orgasmic response, and not an argument for the standard result of a directional selection regime, namely, a *peak* at the optimum?
It's a bit confusing, because there are two distinct types of variability to keep in mind: one kind involves the fact that some women vary in whether they do or don't have orgasm with intercourse, depending on the occasion—this is the kind of variability that would be selected for under his hypothesis. If selection has been of any appreciable strength, and has been going on at least since the advent of archaic humans, we should expect that nearly all women would have such a conditional response to intercourse, and thus that nearly all women would be capable of orgasm with intercourse under the right conditions. The bad news is that there is no evidence for such a peak at all, that a full third of women rarely or never have orgasm with intercourse, and that as many as one out of ten women don't have an orgasm even once in their lives. There is a small peak in the distribution, but it is located at the non-orgasmic segment of the distribution. In other words, this is the kind of variability he needs to support his theory, and his own data show that the supporting evidence just isn’t there, as I’ll detail in a moment.
But there’s another kind of variability, namely, that some women never have orgasm with intercourse, some women always do, and some women sometimes do and sometimes don't. This kind of variability is the kind that they do document in their study, and this kind of variability would *not* be selected for under his proposed hypothesis, but perversely, he implies that it *would*.
This leaves us with a glaring problem. Under his adaptive scenario, we would expect nearly all healthy women to have a conditional response to intercourse, because that is the standard prediction under genetics and selection dynamics. But this is far from what he himself found. His hypothesis *fails on his own evidence*.

Let me make this very precise. They found in their study the typical percentage of women who rarely or never have orgasm with intercourse, namely, 32%. Plus, they found that 14% of women always had orgasm with intercourse. The percent of women who are not included in their proposed selection scenario is: 32 + 14 = 46%. So nearly half of women, according to their own study, do not have the optimum trait, conditional responses to intercourse, at all. Again, any genetics textbook will tell you that if there is directional selection pressure favoring a particular trait, then over the long term, nearly all of the population will have that exact trait, producing a sharp peak in the distribution, provided there is enough genetic variation. Clearly there is enough genetic variation – we do have women who have the exact trait under selection, i.e., sometimes they have orgasms with intercourse and sometimes they don’t. So how come nearly half of women don’t have the [supposedly] selected trait?

Perhaps surprisingly, the distribution of orgasmic capacity (orgasmic through any means, not just with intercourse) of women is nearly *flat*, spreading from very easily orgasmic, through easily orgasmic, through medium orgasmic capacity, to orgasmic with difficulty, to never orgasmic, with a medium-sized bump at the end, of the 5-10% of women who never have orgasm in their lives. (This new study has an even higher percentage of anorgasmia, but let’s give them the benefit of the doubt.) This new study, documenting as it does the wide variability in orgasmic capacity, gives further support for the flatness and breadth of this distribution. This flat and slightly bumpy distribution, with the only peak lying at the non-orgasm bump, is a very powerful argument against any selective account of female orgasm. No standard directional selection regime produces a trait distribution curve that looks like that – any genetics text shows that standard directional selection regimes (which are all that’s been proposed for the evolution of female orgasm) produce trait distribution curves with clear peaks that increase over time. A flat distribution curve spreading out over the entire possible range of a trait is just *not compatible* with there having been directional selection pressure of any significant kind on the trait.
THIRD CONCLUSION: Spector’s theory that female orgasm evolved by natural selection because it served as a conditional signal for quality males is undermined by his own evidence. Strangely, he fails to recognize this. My guess is that this happened because he didn’t distinguish between the two different types of variability that I delineate above. The key concepts in this argument are all from basic evolutionary dynamics. The trait of conditional orgasmic response is hypothesized to have been under selective pressure; hence, other versions of orgasm and the lack of orgasm would have been selected out, producing over time a population peak around this optimum conditional response. Yet we find that the actual distribution of traits is virtually flat, except for the small concentration of nonorgasmic women. This flat distribution with the bump at the no-orgasm end is prima facie incompatible with *any* adaptive scenario.
The fact that this new study establishes a heritability of .45 for orgasm with masturbation (which is much more revealing than orgasm with intercourse, as far as basic orgasmic capacity goes), is also very damaging to any of the proposed adaptationist accounts, and I'm surprised that technical people aren't saying so. Traits that are species-adaptations, such as, for example, having the capacity for language, or starting off with a good sense of taste, or having a massive brain [Correction: brain size has a heritability of .9; see Hawks' link, below], have heritabilities near zero. Nearly all the variability has been used up, selected out. This is just the end result of what I've just recited about the peaks in distributions. If selection is strong enough and goes on for long enough, variability around the peak gets weeded out through selection, and we're left with just one type plus random mutation and somatic, developmental, and environmental accident. Traits with heritabilities near .5 are not even close to being decent candidates for species-wide adaptations, for just this reason, as is widely known (I thought…).
FOURTH CONCLUSION: Spector’s own heritability results also indicate that female orgasm is not an adaptation. Is it only population geneticists who know that species-wide adaptations have heritabilities near zero? How can it be that an expert on heritability like Spector doesn’t know this? I guess this piece of knowledge might be a casualty of over-specialization.
[Addendum: Hawks gives interesting counterexamples involving bipedalism and hormones in his post. It could be that what we have here is the difference between theoretical predictions and actual outcomes in human evolution. More likely, it has to do with the fact that 1. all the selection scenarios proposed for female orgasm involve directional selection, which *does* predict zero heritability, and 2. many real-life traits do not result from directional selection. My conclusion stands. Spector's heritability results are not compatible with his own or any other proposed adaptive hypothesis. But the rest could be interpreted as overly broad; it depends on how you characterize the traits.]
The wide and flat trait distribution of female orgasm capacity, more than anything, is why I am dubious about the possibility that female orgasm is an adaptation. Intuitively, I absolutely agree that it seems almost impossible that it's *not* an adaptation, but with that flat distribution curve, and now, with this news that it has a heritability around .5, it just doesn't seem that it could be. Especially not if you add to this the fact that there is no credible evidence that links female orgasm to fertility or any aspect of reproductive success.
Add to that the fact that the byproduct view provides both an acceptable alternative evolutionary explanation and one that explains many aspects of the trait that are not explained by any other proposed explanation, and it seems to me that the routine and often mean-spirited dismissals of the byproduct view engaged in by so many evolutionary psychologists and animal behaviorists constitute a serious failure to grasp the evidential challenges facing any adaptive account of female orgasm.
You just can’t do evolutionary biology by theorizing and then hoping the genetics and selection dynamics will go your way. While I feel that there is a terrible dearth of knowledge about female orgasm, there’s also lots of evidence already in, thanks to Kinsey and over 70 years of sex research. We do have information about the distribution of the trait. Now, we’ve got a little bit of new evidence for a biological basis (something that I certainly expected under any evolutionary account, byproduct or no.)
But this case of scientific dysfunction I’ve just laid out has broader implications.
What possesses scientists to make fools of themselves by advocating selectionist explanations for female orgasm, when the evidence they cite -- in this case, the evidence he himself gathered -- tells against the very theory he proposes? It's one thing to propose a theory that has no current evidential support; we can interpret that as a speculation, a research idea that would hopefully spur someone to come up with some evidence to test it. But his own evidence flatly goes against his theory. Do we have physicists with theories that say things fall up, citing evidence that shows that things fall down? I analyze a couple of other cases like this in my book. They’re all cases in which the author seems to have a deep prior commitment to an adaptive view. I see an associated sense of urgency here: the new evidence *must* support some adaptive view or other; actually, it seems to support this very theory! I’m not at all interested in the psychology, of deep confusion or self-deception or whatever. What interests and concerns me is the failure of the self-correcting function of the scientific community.
Who is Spector talking to? We can assume that he has discussed his data and his evolutionary speculations with colleagues. I checked the web, and he has repeatedly over the years written rather authoritatively on the evolution of human sexuality and female orgasm. Doesn't anyone around him know any genetics? Why didn't he even check what the dynamics of selection would be for his proposed scenario? Does he understand how directional selection narrows the expected distribution of a trait? He's publishing on heritability here. Doesn't anyone around him know the evolutionary meaning of a heritability of .5?
-----I want to emphasize that nothing I’ve said so far in this paragraph depends in any way on being partisan. Test this by looking the claims up in any genetics text. -------
His research focus is on twin studies, which means he spends nearly all his time doing heritability and statistics. The technical journal paper does not include his adaptationist speculations, but it does cite the statistically hopeless Baker and Bellis research on sperm upsuck. Bad sign. But, of course, most scientists’ understanding is shaped by what the author says in the mass media. At any rate, the scientific processes of criticism and uptake, which are necessary conditions for scientific objectivity and scientific knowledge, clearly broke down in this case. He either spends all his time alone, or surrounds himself with ignorant people, or fellow-travelers, or he doesn’t listen when people tell him things.
Is there a possibility I’m missing?

OH, and he is suffering from the closing off of legitimate alternatives that occurs when bias is in operation, adaptationist bias. Thus, he is unable to see what is before his face: he has documented clear evidence *against* female orgasm being an adaptation at all.
It seems that I should respond up front to a well-meaning but mis-informed criticism that some folks are getting over-excited about.

John Hawks posted on his blog the provocative:
"I guess I'm as "technical" a person as has considered the issue lately, and Lloyd is just wrong about [the heritability issue]. Certainly it is true that Fisher's Fundamental Theorem predicts that the heritability of a trait will decrease under directional selection, but Lloyd has provided us no reason to suppose that selection on female orgasm need have been directional in its pattern."
He's right. But the reason I considered exclusively directional selection scenarios is that those are *the only ones that have ever been proposed*. Again, the conclusion is sound; under Spector's and all the other adaptive theories under consideration, the heritability should be near zero, not .45, as he found.

June 11: Addendum #2: John Hawks has revised his position in light of the above, and acknowledges that my arguments against Spector are right to the point. Do check out his very interesting pessimistic conclusions regarding the possibilities of ever confirming an adaptive account of female orgasm.

June 18: Addendum #3: Dr. Petra Boynton, a sex researcher in England, has two worthwhile posts addressed to the Spector issue:, I find the methodological problems she raises particularly interesting. In my book, I object to the categorization of women's lack of orgasm during intercourse as a "dysfunction"; Boynton goes after a related topic here: "But the main problem with the questions asked, was that frequency of orgasm doesn’t equate to orgasmic dysfunction. Because you don’t have an orgasm ‘frequently’ doesn’t make you dysfunctional. Only this research assumed it did." She also found an amazing quote by Spector: “Perhaps women who had orgasms too easily weren’t very good selectors." Too easily. It follows.










Evolutionary Psychology 3: 347-354

The Human Nature Review

Let a Thousand Orgasms Bloom! 

A review of The Case of the Female Orgasm, by Elisabeth A. Lloyd. 2005. Harvard University Press: Cambridge, Mass. 311 pp.

David P. Barash, Department of Psychology, Box 351525, University of Washington, Seattle, Wa. 98195, USA.

In The Case of the Female Orgasm, Elisabeth A. Lloyd has taken a really terrific topic and written a really terrible book. I say this with sincere and manifold regret, first because female orgasms pose fascinating and important questions, that warrant serious attention from evolutionary biologists. Second, I particularly would have loved to find a worthwhile book on this matter, not least because I am working on my own book-length treatment of it and other "womanly mysteries." Thus, for all the interest (scientific no less than personal as well as prurient) attaching to female orgasm, there are many other dimensions of womanhood that also remain to be explained in convincing evolutionary terms: Why is ovulation concealed? Why is it so often synchronized? Why does menopause occur? Ditto for menstruation. Why do women have prominent breasts even when not lactating? (Barash, in preparation).

And finally, I would like to be kinder and gentler with Lloyd's book because - given the realities of reciprocal altruism - the more books I write, the more am I inclined to say good things about the efforts of others, hoping perhaps that they will return the favor … or at least, not be terribly nasty about my next offering! But I need to be honest, too.

The topic is straight-forward enough: why do women experience orgasm? The male counterpart is easy enough for evolutionists to explain, but - despite an abundance of theorizing - no one has yet demonstrated a clear-cut fitness benefit that accrues to orgasm in women. Indeed, for many years, biologists including yours truly believed that female orgasm was unique to human beings, albeit no less a mystery. Now, we know that females of many nonhuman primates and maybe even some nonprimates experience orgasm. But we still don't know why.

One possibility, championed most prominently by Donald Symons (1979), is that the female orgasm is an evolutionary by-product of male orgasm, a neutral tag-along trait that persists because it is adaptive in one sex, and, because of its developmental underpinnings, is difficult to lose in the other. The preferred metaphor is/are male nipples: clearly adaptive in women, nipples are nonfunctional and evidently nonadaptive in men, yet they presumably persist among the latter because of their benefit to the former. This is the view that Dr. Lloyd favors.

So far, so good. The problem - among many - is that she doesn't simply favor it; rather, she is so ardent in her commitment and so dismissive of other, adaptive possibilities that her book is more a rant than an even-handed effort to expound upon and demystify a genuine, unsolved scientific controversy. Moreover, Lloyd's zealousness is compounded by a regrettable lack of biological sophistication plus plain old-fashioned lousy writing. Some examples of the latter: "The crucial point is that, whatever people's intuitions are regarding the obviousness of what should be the case in evolution, I have already argued, in relation to the adaptive stories current at the time, that there is no credible evidence that orgasm correlates with reproductive success (pg. 166)." "I should note that even though evidence can be used to challenge background assumptions, there are yet further background assumptions required to link the challenged background assumption to this evidence. In general background assumptions are challenged with relation to a particular set of other background assumptions and the public standards of a community (pg. 249)." How about this background assumption: decent writing? Perhaps we should take up a collection to help Harvard University Press hire an editor who edits.

Okay, so Dr. Lloyd is not a stylist. Sadly, she is not much of a biologist, either. Much of her argument turns on the question of whether a given phenotype is an adaptation, and in order to fit her Procrustean bed (pre-constructed to accord with her commitment that lots of traits aren't adaptations, she defines adaptations so narrowly as to exclude most of them! Thus, we are offered the extraordinary claim that sickle-cell disease is "the best, most elaborated case of a human adaptation." (pg. 12) What about binocular vision, or the human hand with its opposable thumb? Or bipedal locomotion, or the kidney's prowess at filtration, the heart as pump? Or our large, multi-facetted brains, for Darwin's sake? (Hint: since no iron-clad historical sequence for such phenotypes have yet been adduced, and, moreover, no clear Mendelian basis for such traits have been identified, they don't qualify in Lloyd's opinion as adaptations. With so limited a perspective, no wonder Dr. Lloyd has such a hard time perceiving female orgasm as a possible - indeed, a likely - adaptation.)

Ironically for a book with the subtitle "bias in the science of evolution," The Case of the Female Orgasm is marinated in bias: against "adaptationism," "androcentric thinking," and heterosexuality, and in favor postmodernist "social constructivism" as well as anything ever written by Stephen Jay Gould. Not surprisingly, Gould godfathered Lloyd's argument, basing one of his Natural History columns upon it, and - word has it - lobbying hard and successfully at Harvard University Press on behalf of her manuscript.

Moreover, this isn't really a book about the female orgasm; rather, it is about the debate over the female orgasm, consisting mostly of criticisms of other people's data and interpretations. There is much to be said for an occasional Hercules, cleaning out the Augean Stables of ill-founded scientific dogmatism. But Lloyd labors are less Herculean than they are self-defeating, as her single-minded determination to argue against any adaptive function for the female orgasm not only diminishes her credibility but highlights her own biological naivety.

Thus, Lloyd makes much of the fact that orgasm varies "widely across women," arguing that this is "exactly what would be expected if it were not under direct selection pressure" (pg. 133). She is correct that traits under very strong selection pressure generally show little variation (the variance in number of heads per person is indeed low). But a range of variability is definitely not, in itself, evidence that a trait is not adaptive: what about human height, weight, intelligence? Did they not almost certainly evolve under selection pressure? Admittedly, maybe the answer is no, but common sense plus basic biology suggests otherwise; the fact that such traits vary may be attributable to several factors, suggesting the maintenance of underlying genetic variation via a diversity of mechanisms.

Lloyd claims further that orgasm's phenotypic plasticity "is evidence that selection has not acted on the trait at all" (pg. 135). Nonsense. Selection can favor phenotypic plasticity. Indeed, it often does! The fact that human beings speak thousands of different languages is testimony to vast plasticity, but is NOT evidence that selection hasn't acted on the ability to speak languages.

Lloyd also makes much of the fact that most women do not experience orgasm every time they engage in sexual intercourse, claiming that this somehow casts doubt on the possibility that orgasm is an adaptation. This is like saying that because lions don't always hunt, or don't always succeed when they do hunt, hunting isn't adaptive. The reality, of course, is that lions have been selected for phenotypic plasticity with regard to their hunting: being more likely to do so in circumstances than others. And indeed, one of the more plausible hypotheses for female orgasm relies on the observation that it occurs at some times and not at others … wherein may lie its adaptive value:

Several decades ago, while a graduate student, I noted that when a subordinate male grizzly bear mounts a female, his head swivels constantly over his shoulder as he anticipates the arrival of any dominant boar, who would rapidly supplant him. Not surprisingly, subordinate grizzlies ejaculate quickly whereas dominants are substantially less rushed. I have no idea whether grizzly sows experience orgasm, but it seems likely that if they do, it would be more likely when copulating with the latter than with the former. And this, in turn, led me to wonder whether female orgasm is a signal whereby a female's body tells her brain that she is sexually engaged with a dominant individual. If this is the adaptive significance of female orgasm, then we certainly would not expect orgasm to occur with regularity, and would be altogether misled if we took its seemingly erratic occurrence as evidence that it does not serve an evolutionary function.

Lloyd claims to marshal evidence to the contrary, which includes the claim that females cannot be assumed capable of discriminating "genetically-based differences among potential mates" and deciding, as a result, which phenotypes would constitute better mates (pg. 196). Perhaps she has not yet heard of sexual selection and the role of female choice. If so, I suspect most readers of this review could suggest some references, probably off the top of their heads.

Elsewhere, Lloyd points to the "puzzling data on the relative infrequency with which women experience orgasm with intercourse," arguing that "under the common assumption that the capacity for orgasm is designed as an adaptation to encourage and reward intercourse, this infrequency must be seen as a design flaw" (pg. 112). What, pray tell, is wrong with design flaws? Evolutionists know that the biological world abounds in them: our narrow birth canal, the location of the prostate and of the exit site for the retinal nerve. It is the advocates of "intelligent design" and of similar drivel who have difficulty contending with design flaws; biologists understand that since there is no designer, flaws are to be expected, and their existence by no means comprises evidence against evolution by natural selection of the traits at issue. (At the same time, of course, flaws provide impressive evidence that a purported divine designer is either incompetent, indifferent, lazy, or, on occasion, downright malign.)

In her extended polemic, Lloyd makes much of the fact that female orgasms are typically clitoral and rarely vaginal, which once again is supposed to militate against the adaptationist contention that orgasm is related to fitness maximization, via heterosexual intercourse. There is little doubt that the clitoris is homologous to the penis (a connection that is fundamental to Symons' by-product theory, so strongly favored by Lloyd), and that the two organs derive from the same embryologic substrate. Accordingly, it is unsurprising that clitoral stimulation is intimately connected to female orgasm, just as penile stimulation is to its male counterpart. That said, it is altogether consistent with a range of adaptive interpretations that female orgasm should be more readily evoked clitorally than vaginally; as all but the most blinkered nonevolutionists realize, evolution is an inefficient process, in which phenotypes are cobbled together from embryologic and historical antecedents. Under various scenarios, it might be more adaptive yet - and certainly, more desirable for those involved - if women could achieve orgasm by eating chocolate, painting their toenails, thinking pure thoughts, and so forth, but insofar as orgasms are keyed to penises and clitorises, that's what natural selection has had to work with.

This, in turn, leads to another possibility - indeed, perhaps likelihood: What if female orgasm isn't an evolutionary by-product, à la Symons and Lloyd, but rather, orgasm via masturbation is? Moreover, what if the biological significance of female orgasm derives from clitoral stimulation achieved - albeit inefficiently - via (gulp!) old-fashioned heterosexual intercourse, because of some yet-to-be clarified adaptive value? The horror, the horror!

Lloyd seems downright incensed by the fact that most analyses of female orgasm emphasize its occurrence during heterosexual intercourse and give short shrift to orgasms induced during female-female encounters or via masturbation. The reason for this emphasis, I submit, is simple, and not because of a male chauvinistic bias on the part of researchers (many of whom are women). Rather, evolutionary science suggests that insofar as there is likely to be an adaptive value to female orgasm, it is almost certainly manifest during heterosexual intercourse. I doubt that women have been endowed with the capacity for orgasm simply as a beneficent gift from a generous god, even though neither I nor my fellow ardent adaptationists (John Alcock's phrase) are unaware of the inelegantly labelled "orgasm/intercourse discrepancy," supposed by Lloyd to weigh heavily against the adaptive significance of female orgasm itself. But by the same token, one might point out that male orgasms are more reliably achieved if a man stays home and masturbates than if he goes out on the town, seeking a sex partner; no one would seriously claim, however, that this is evidence suggesting that male orgasm during intercourse is nonadaptive! Changing the metaphor, I might be able to achieve a kind of satisfaction (albeit temporary) by filling my stomach with sand, or chewing coca leaves, or I might even force myself not to eat altogether, but this doesn't mean that consuming food is nonadaptive.

Don't misunderstand: I have nothing against masturbation or same-sex relationships, or carnal satisfaction achieved via poetry, sunsets, cooking utensils, antique harpsichords or even consenting animals. Quite the contrary. Let a thousand orgasms bloom! Indeed, in a world both overcrowded and increasingly infected with dangerous sexually transmitted diseases, I'd heartily recommend masturbation in particular as the epitome of safe sex. My point is that just because something (e.g., female orgasm) can be achieved in diverse ways (e.g., masturbation) does not argue against it having evolved because it is particularly adaptive in a specific, different context (e.g., heterosexual intercourse).

Is it androcentric, phallocentric, or some other kind of "centric" to suggest this? Maybe so, but the fact that a hypothesis might be "male centered" does not necessarily make it wrong, any more than the fact that population biology is female centered does not make it wrong. Moreover, sexual intercourse is no more male-centered than it is female-centered, although it is, I admit, heterosexually centered. There is indeed a reproductive bias to evolutionary biology generally, and my advice is that anyone who finds this objectionable should find a different line of work.

"There are elements of androcentrism," writes Lloyd, "and heterosexual bias operating in procreative focus as it applies to female orgasm, because procreative focus concentrates only on the kind of sex that is reliably associated with male reproductive success: intercourse" (pg. 234). This raises nonsense to new levels. Is male reproductive success somehow more tied to sexual intercourse than is female reproductive success? When last I checked, direct (Darwinian) reproductive success - for females no less than males - requires one or more acts of sexual intercourse, involving at least one male and one female, and as a result of which males and females experience precisely equal reproductive success. The variance between males and females may well differ; the reproductive success of the average female in any sexually reproducing diploid population is exactly equal to that of the average male.

I first became aware of The Case of the Female Orgasm when I received a phone call from a reporter asking for "my side" of "the controversy." I didn't know that I had a side. Turns out Dr. Lloyd had unearthed - and misrepresented - part of a single paragraph in a chapter I had co-written with my former graduate student, William Bernds (Bernds and Barash, 1979). This manuscript was not concerned with female orgasms; rather, it sought to identify some of the factors responsible for "early termination of parental investment in mammals, including humans." In it, we felt obliged to mention, in passing, the curious fact that Kinsey's team as well as Masters and Johnson had commented on a possible correlation between "spontaneous abortion," the topic we were treating, and female orgasm. This is hardly a theory for the evolution of female orgasm, especially not for ardent adaptationists, and we did not present it as such. indeed, the fact that Lloyd resurrected it in her book only to poke fun would be, in itself, no more than silly.

But this trivial episode may hide more than meets the eye, bespeaking how desperate Lloyd is to find straw men to dispute. Rhetorically, it might work; scientifically, it stinks. Interestingly, this is a practice with which Stephen Gould - of whom Lloyd is an acolyte - was not unfamiliar: trolling for targets of opportunity in the scientific literature, which, once suitably distorted, appear to strengthen one's case.

On a similar note, after describing and criticizing Baker and Bellis (1993), Lloyd observes parenthetically "There is an unanswered question about how the Baker and Bellis paper ever got published in Animal Behaviour, the flagship journal in the field" (pg. 232). Firstly, as someone who - at least in the past - published quite often in Animal Behaviour, and has often served as an editorial consultant, I can't imagine that anyone other than Dr. Lloyd considers it the "flagship journal" in human sociobiology, evolutionary psychology, or human reproductive biology, given that Animal Behaviour virtually never publishes articles concerned with Homo sapiens. This leads to the "unanswered question" whether Lloyd has ever read this journal that she ostensibly so reveres. More troubling is the snide tone of her remark itself. What, precisely, is she saying? That she posed this question (how did Baker and Bellis ever get published) to the editors of Animal Behaviour, which went unanswered? That the question arose in her mind, merely to languish unanswered? That it ought to arise in ours? That there is a conspiracy to publish articles with which Dr. Lloyd disagrees, or of which she disapproves? Readers beware: the evolutionists are coming, the evolutionists are coming!

Since she raised the matter, one might ask the same "unanswered question" concerning Lloyd's own book. How did it ever get published by one of the flagship publishers of academic and serious trade books? After all, The Case of the Female Orgasm merely recycles Symons' already familiar hypothesis, casts aspersions (some of them ad hominem) on legitimate researchers, misrepresents or misconstrues important aspects of evolutionary biology, and is poorly written to boot.

Is there anything worthwhile to be gleaned from The Case of the Female Orgasm? Actually, yes. The bibliography is extensive. I am grateful, as well, to Dr. Lloyd for pointing out that the "data" for "uterine upsuck" secondary to female orgasm as a possible contributor to fertilization (Fox, Wolff and Baker, 1970) derive from just one woman. And similarly, for pointing out that the Baker and Bellis (1993) data set on "flowback" is highly skewed and inadequate. But don't take Lloyd as a statistical adviser: she is so desperate to critique Baker and Bellis that she comes up with the unique and stunning claim that nonparametric statistics require larger sample sizes than do their parametric counterparts.

Lloyd is also effective in pointing out that even nonadaptive, by-product explanations are legitimately "evolutionary," despite which they are the Rodney Dangerfields of biology: they don't get any respect. But even here, she falters, following her now-familiar procedure of creating a straw man by exaggerating and misrepresenting the adaptationist approach, so as to seem oh-so-reasonable in disputing it. Thus, Lloyd claims that according to adaptationist thinking, "no byproduct explanation should ever be accepted" (pg. 252, emphasis in original). But no biologist, to my knowledge - even the most adaptationist-addled - disputes the byproduct interpretation for the evolution of male nipples, a perspective that Lloyd has repeatedly invoked in her own book!

I suggest that such explanations are - as well they should be - treated essentially as null hypotheses, against which adaptive interpretations are assessed. In this regard, the Symons' by-product hypothesis remains, even now, a viable possibility. Konrad Lorenz once remarked that every good scientist should discard at least one cherished hypothesis every day before breakfast. Although I don't recall him following his own advice, and although I strongly disagree with much - indeed, nearly everything - in Lloyd's treatment of adaptationism versus byproduct-ism, her warning to evolutionists about the legitimacy of the latter is well taken: we must ask ourselves "whether anything more than lip service is being paid to the foundational assumption from evolutionary biology that alternative, nonadaptive explanations are part of the toolkit of evolutionary theory" (243).

As to the future, I place myself unabashedly in the Panglossian, ardent adaptationist, natural selection-besotted camp. Why? Because it works. As to Lloyd's camp, she complains about a lack of evidence that "links female orgasms to either improved fertility or to increased birth rates or reproductive rates," after which she notes "Without it, those who take an adaptationist line are relying on a future promise of such evidence being produced " (pg. 222). Just so. That is what a research program is: efforts based on the future promise of results. If the promise is not fulfilled, one looks elsewhere … maybe even to the by-product hypothesis. The final arbiter is fidelity to objective, empirically demonstrable findings. Lloyd, by contrast, reveals much of her agenda when she acknowledges that her sympathy with the "by-product" theory arises because it is the "account with the closest ties to the feminist value of separating definitions of women - including women's sexuality - from women's reproductive functions" (pg. 237).

Rather than "continuing to fight for definitions of women that are not based on their reproductive roles" (pg. 237) - Lloyd's admitted bias - an adaptationist approach would indeed take a close look at the possible "reproductive role" of female orgasm … not to define or constrain women, or to "privilege" heterosexuality, but for the old-fashioned reason that people do science: to learn something that we might not otherwise know. Thus, I suggest that my fellow adaptationists might profitably devote attention to the following questions (some of which have already been broached, but all of which warrant more research): Is there evidence that female orgasms correlate with a particular suite of circumstances? With any particular characteristics of a female's partners? Is there any correlation between female orgasm and fertilization? Between female orgasm and successful termination of pregnancy? Between female orgasm and fitness - inclusive no less than Darwinian? What is the role, if any, of female orgasm when it comes to mate selection? What about oxytocin and its male analog, vasopressin? And - perhaps most important - how can we encourage people to prioritize empirical research and legitimate theory-building over the back-biting, ideological excess, and the nonsense of social constructivism so regrettably manifested in The Case of the Female Orgasm

Baker, Robin R. and Mark A. Bellis. (1993). Human sperm competition: ejaculate manipulation by females and a function for the female orgasm. Animal Behaviour 46: 887-909.

Barash, David P. in preparation. Womanly Mysteries: a Darwinian look at what we don't know about the female body.

Bernds, William P. and David P. Barash. (1979). Early termination of parental investment in mammals, including humans. In N. A. Chagnon and W. Irons, eds., Evolutionary Biology and Human Social Behavior: an anthropological perspective. Duxbury Press: No. Scituate, Mass.

Fox, C. A., H. S. Wolff, and J. A. Baker. (1970). Measurement of intra-vaginal and intra-uterine pressures during human coitus by radio-telemetry. Journal of Reproduction and Fertility, 24: 319-336.

Symons, Donald. (1979). The Evolution of Human Sexuality. Oxford University Press: New York.

Barash, D. P. (2005). Let a Thousand Orgasms Bloom! A review of The Case of the Female Orgasm by Elisabeth A. Lloyd. Evolutionary Psychology, 3:347-354.