Why is the human vagina so big?

We are obsessed with penis and testicle size. Yet, we can barely say "vagina" and when we do we're usually talking about the vulva.

Everyone's come across some article somewhere on-line that is thrilled to share how big human penises really are, for primates, and to explain why they evolved to be so big. It's not really the length, but the girth. Alan Dixson is your go-to on this. He's conservative in his assessment of the literature on penis size and even he concedes that human penis "circumference is unusual when compared to the penes of other hominoids (apes)" (p. 65 in Sexual Selection and the Origins of Human Mating Systems).

A favorite explanation for the big phallus is female mate choice, that females selectively make babies with males who have larger and, presumably, more pleasurable semen delivery devices. This is backed up by studies. When life size projections of naked men are shown to female subjects, they say they find the ones with bigger ones to be more attractive. [This is exactly how mate choice works where I live, how about you?]

Other explanations include male competition. If you can deliver your package to the front yard but the other guy can deliver to the front door, his is more likely to be carried inside the house first. Or, if he can steal away what you just delivered, then, again, his package has yours beat. Thanks to his big penis he's more likely to pass on his winning penis genes than you are to pass on your loser penis genes. Loser.

All this is just terribly fun to write about and I'm not even going nuts (gah) like they do. And they do. They really do. And all over the Internet they do: "Evolution of human penis" gets 53,000 hits just on scholar.google alone, and about 832,000 on Google.

But doesn't it make sense that for a penis to be somewhat useful it has to be somewhat correlated to vagina size?

I'm talking about all penises in the universe and all vaginas too. Sure there's variation, but a penis can't be too wide. It helps to be long, probably, but it can't be too long.

So neither pleasure nor psychology need matter at all, just function associated with some sort of fit. Pleasure and psychology are never invoked to explain penis morphology in other animals. If anything, it's the cornucopia of horrifying, not pleasing, animal penises that begs for evolutionary explanations.

Wouldn't you explain the size and shape of the key by the size and shape of the lock? So wouldn't it be a little more scientifically sound to hypothesize that the human penis is sized and shaped like that because it fits well into the human vagina?

Sure, it gets chicken-and-eggy or turtles-all-the-way-downy, but c'mon. Isn't it a bit obvious that the privates that fit inside the other privates are probably correlated? You'd think that even the people who have never had intercourse would default to this explanation for the evolution of the human penis.

Figure 2. Examples of genital covariation in waterfowl.

(A) Harlequin duck (Histrionicus histrionicus) and (B) African goose (Anser cygnoides), two species with a short phallus and no forced copulations, in which females have simple vaginas as in Fig 1a. (C) Long-tailed duck (Clangula hyemalis), and (D) MallardAnas platyrhynchos two species with a long phallus and high levels of forced copulations, in which females have very elaborate vaginas (size bars = 2 cm). ] = Phallus, * = Testis, ★ = Muscular base of the male phallus, ▹ = upper and lower limits of the vagina.

doi:10.1371/journal.pone.0000418.g002

But we're rarely, if ever, told that human penises are relatively girthy because human vaginas are. It's always about male competition or female preference.

Sure, we may be a little weird compared to our close relatives for not having a baculum (penis bone), and maybe that's the sort of thing you want to explain for whatever reason, but does human penis size and shape need a uniquely human story?

Assuming it's correlated to the vagina like it probably is in many other species,* then no it doesn't... unless the size and shape of the human vagina has an exceptional story.

Does it? We wouldn't know. There are zero (look!) articles titled "Why is the human vagina so big?"

Until right now.

Here we go. If we were going to answer it the same way we've long explained the human penis, and other animal penis shapes, then we've got a few ideas...

Because walking upright made the vagina conspicuous and males thought a bigger vagina was better. Because big vaginas outcompete small ones at catching sperm. Because of male pleasure from coitus with a big vagina. Because of heat dissipation or thermoregulation. Because of a tradeoff with brain size.

And of course, we'd need to demonstrate that the human vagina is in fact larger, relative to body size, than the vaginas of other primates. Regardless, a sound answer to the question of vagina size and shape focuses on childbirth, wouldn't you say? She's got to be big enough to push out a baby and, for humans, it's a great big baby. 

So if there's an exceptionally human story for the great big human penis, that exceptional story originates not in a woman's orgasms, not in her pornographic thoughts or her lustful eyes, but in her decidedly unsexy "birth canal."

And I dug up a nice little note to explain this to us all written by Dr. Bowman, a gynecologist, back in 2008 for the Archives of Sexual Behavior

That note is magnificent. It starts out giving the only vagina-size-based, not to mention childbirth-based, explanation for human penises that I can find in the literature (which is thankfully cited by Dixson in his book mentioned above). But it still manages to bring the explanation beyond the vagina and onto another proud triumph: "In sum, man’s larger penis is a consequence of his larger brain."

After you clean up the coffee you just spat onto your computer screen, you can read it all for yourself up there in the figure.

Guess who didn't read it? That study in PNAS, mentioned above, that showed women naked penises, got a high attractive score for the big ones, and thinks that's evidence for mate choice now, today, let alone back when (I'm going to speculate that) women had a tiny bit less of it.

Point is, the literature rages on with the special explanations for the big penis with nary a big vagina in sight.

But you heard it here, at least.

Childbirth is why the human vagina is so big and, consequently, why the male penis is so big. It's pretty straightforward. Yet we're still left scratching our heads as to why the penis question endures.

Is evolutionary science averse to big vaginas?

Does nobody love a big vagina?

Because that's just ridiculous. Everybody came from one.



*Unfortunately a few scholar.google searches led me to find no cross-species comparisons of mammalian vagina lengths or any vaginal measures. It may be out there, but I haven' t found it. I found some measures for bitches... DOGS! And some heifers... COWS! So I've got to compile some data if I'm to do this properly. Baby size might be a way to do this.

**UPDATE. p. 73 in Dixson has Figure 4.3 with nine primate species' penile and vaginal lengths plotted. Thanks Patrick C for reminding me where I'd seen something like this and where to point readers!

Just-So Babies

If you've ever watched a baby eat solid foods, that's DuckFace.

If you've ever seen a shirtless baby, that's DadBod.

Why are we so into these things, whatever they are, right now?

Because whether we realize it or not, they're babylike, which means they're adorable. And all things #adorbs are so #totes #squee right now for the millions (billions?) of social media users in our species. And if they're babylike, they're especially adorable to women and women are more frequently duckfaces than men. And women are increasingly open to embracing, maritally, the non-chiseled men of the world...who knew?

Well, anyone and everyone who's spent a damn second raising a baby, that's who. Especially those with mom genes.

Understanding babies, how they develop, and our connections to them while they do so is key to explaining just about everything, and perhaps literally eh-vuh-ray-thing, about humanity. How can I be so sure? Well aren't you?

We all know that the most attractive women are the ones that look like babies. 

source

And to help Nature out, makeup, lasers, and plastic surgery neotenize us temporarily or permanently, making our skin smooth, our eyes big, our lips pouty, our cheeks pinchable and rosy, and our noses button-y.

That stuff about beauty is common knowledge isn't it? We do these things to ourselves because of our evolved preferences for babies. We find them to be so extremely cute that this adaptive bias for babies affects much of the rest of our lives. Beauty is just the tip of the iceberg because, like I said, babies explain everything: DuckFace, DadBod, ...

And, yes, I do have more examples up my sleeve.

All that weight we gain while pregnant? You think it's to stockpile fat for growing a superhuge, supercharged baby brain both before and then after it barely escapes our bipedal pelvis?

Me and Abe, with hardly an inkling that there's still a whopping five more weeks ahead of us... suckers.

Or maybe I gained 20 pounds above and beyond the actual weight of the pregnancy so that I could protect my baby from calorie lulls from disease or food shortage, especially when those things happened more frequently to my ancestors.

Nope. And nope.

Pregnant women gain all that weight so that its lightning fast loss while lactating leaves behind a nice saggy suit of skin for the baby to grab and hold onto--not just on our bellies, but our arms and legs too. Our ancestors were dependent on this adaptation for quite a while, but over time mothers and infants became less dependent on it when they started crafting and wearing slings. Slings reduced selection on a baby's ability to grasp, you know.

Before slings, selection would have been pretty intent on favoring baby-carrying traits in both mothers and babies. For example, the way that our shoulder joints are oriented laterally, to the side, is unlike all the apes' shoulders which are oriented more cranially, so they're always kind of shrugging. You think we have these nice broad shoulders for swinging alongside us while running, for seriously enhancing our throwing ability, and, of course, for making stone tools? 

No. No. No.

All that's great for later in our lives, but our lateral facing shoulder joints are for being picked up and carried around while we're helpless babies. Our sturdy armpits are necessary for our early survival. And, biomechanically, those shoulder joints are oriented in the optimal way for carrying babies too. It's a win win. Combine that with the shorter hominin forearm, oh, and that itty-bitty thing called hands-free locomotion and it's obvious that we're designed to carry our babies and also to be carried as babies.

Bums come into play here too.

You probably think your big bum's for bipedal endurance running don't you? Or you might assume it evolved to give a stone-tipped spear a lot of extra oomph while impaling a wooly rhino hide.

Wrong. And wrong again.

Our big bums develop early in life because, like armpits, they build grab'n'go babies as well as well-designed grown-up baby carriers.

source

Bums plop nicely on a forearm and most certainly give babies and moms an advantage at staying together. Bums on moms (if not completely liquefied and fed to baby) steady her while holding such a load and also provide something for a baby slung on her back to sit on. Once babies lost the ability to grasp onto moms, babies' bodies had to adapt to be portable objects and moms bodies had to adapt to never drop those portable objects (at least not too far). No doubt big bums, like sturdy armpits, evolved before slings and home bases were ubiquitous in our species. 

Here's another one: The pregnancy "mask."

All those pigmentation changes that we describe as a side effect of the hormones are much more than that. Those new brown and red blotches that grow on a mother's chest and face, those are functional. They're fascinators. A mother's body makes itself more interesting and loveable for the busy, brainy baby on its way. Once we started decorating our bodies with brown and red ochre and pierced shell, bones and teeth, selection on these biological traits was relaxed. But they still persist. Why not? A human baby can't be over-fascinated, can it?

Oh, and fire. That was the best thing that ever happened to babies which means it was the best thing that ever happened to everyone living with babies. Quiet, serene, fascination, those flames... which also happen to process food for toothless babies whose exhausted, stay-at-foraging parents, would much rather swallow the food they chew up for themselves.

The baby also grows fascinators of its own. The big long hallux. Yep. Our big toe is long compared to other apes'. This is where you say it's an adaptation for bipedalism but you'd be only half right.

© naturepl.com / Ingo Arndt / WWF

The length makes it easier to reach with our mouths, as babies. And we teethe on that big toe. Imagine a world with no Sophies! That's what our ancestors had to deal with. Toes as teething toys doesn't seem so ridiculous when you remember that our long thumbs evolved for sucking.

Anyway, this long hallux was a bit unwieldy so thanks to a lucky mutation we stuck it to the rest of the foot and this turned out to work rather well for bipedalism.

Now that it's been a few minutes into this post, you must be sitting there at your computer thinking about boobs.

Yep, babies explain those too! The aesthetic preference for large breasts, by both males and females, is just nostalgia and allometry. You know how when you go back to visit your old kindergarten it looks so tiny compared to your memory? While you're a small human, you spend quite a lot of time with breasts, focused intently on them. But grow your early impression of breasts up in proportion to your adult body's sense of the world and, well, that's quite a big silicon kindergarten!

Your desires, your preferences, your tastes, your anatomy now, your anatomy when you were a baby... everything is babies, babies, babies. Even bipedalism itself.

Gestating a large fetus would not be possible if we were not bipedal. Think about it. All apes are bipedal to a significant degree. What pressured us into being habitual bipeds? Growing big fat, big-brained babies, that's what. Can you imagine a chimpanzee growing a human-sized fetus inside it and still knuckle-walking? I doubt the body could handle that. The spine alone! If you walk upright and let your pelvis help to carry that big fetus, you're golden. Obviously it worked for us.

I could go on forever! But I'll just give you one more example today. It's one you didn't see coming.

Women live longer than men, on average, and a large portion of that higher male mortality rate (at older ages) is due to trouble with the circulatory system. Well, it's obvious why. I'm looking at my arms right now and, complementing these brown and red fascinators, another part of my new mom suit is this web of ropy blue veins. Is this because my baby's sucked up all my subcutaneous fat from under my saggy skin, or... Or! Is it because my plumbing's stretched after housing and pumping about 50% more blood than normal by the third trimester. If my pipes are now, indeed, relatively larger for my blood volume and my body size then, all things being equal, that should reduce my risk of clogging and other troubles. Most women experience a term pregnancy during their lives. I'm sure this explains most if not all of the differences in mortality between men and women.

Like I said, that's just the start. And although I haven't provided evidence for many of the things I wrote, that shouldn't matter. These are just-so stories and they're terribly fun to think about. They're nothing close to approximating anything as lovely as Kipling's but they're what we humans do. If you're not a fan of today's post, hey, it's not like it passed peer review!

The Nair-do-wells, and their evolutionary message

In what, if you'll forgive the pun, is a barely visible revolution, it appears that women are throwing away their razors (sorry, Nair!).  As Beverley Turner put it in The Telegraph last week, "Ladies, breaking news: it is time to step away from the molten wax and let our lady gardens grow free." Maybe it's because Gwyneth Paltrow told Ellen DeGeneres that she "rocks a 70s vibe down there", or maybe it's just, like clothing, another changing fashion, but pubic hair is back.  Whether this is caused by, or will be followed by the porn industry is something that, surely, many university professors will be seeking grants to study.

This should be especially interesting to the evolutionary psychology industry, because of their determination to document the Darwinian reasons for the hard-wiring for every element of behavior.  In the old, naive days, their academic ancestors showed how clearly pubic hair evolved as a sexual-display trait, to ensure that males would be interested (as if that were necessary!).  Otherwise, if it were not all about mate choice and sexual selection, what was it doing there?

Well, perhaps it wasn't just a sexual attractant, but instead, a signal by the females that they were no longer girls, but women, ready and able to mate and conceive.  No wasted sperm by males who would otherwise be attempting to make the Shakespearean beast with two backs with those who couldn't yield the offspring by which the promiscuous males were so driven to propagate.  Or maybe it "aids in the wafting of human pheromones", never mind that there's no uncontroversial evidence that humans even have much in the way of active vomeronasal organs, or pheromone receptors. 

Whatever the explanation, strong sexual selection clearly mandated this particular patch.

But if so, how could it possibly be that for the past generation the fashion was no pubic hair at all?  After all, why would looking like a pre-pubescent girl attract men?  How could any woman give up her come-on signal, that so clearly, we were told, evolved as a fundamental necessity for evolutionary existence?  We haven't tried to explore what the evolutionary behavior people said about this patchwork trend in patchwork, but given it's lascivious appeal surely there are articles and books galore, retrofitting Darwinian explanations to that once-new (and now obsolescing) hirsute reality.

But that doesn't really work if we are hard-wired to respond to that View.  It may be a conundrum.

This is not (only) a prurient post!
We must leave this mesmerizing topic, to show that we ourselves are not dwelling on it for its reader-appeal.  There are many similar issues, that generalize the point, and it is in fact an evolutionary one!

Nov 24's NY Times book review section reviews two new books dealing with the philosophy of dilemmas, specifically the trolley dilemmas, which goes like this: If you could divert a trolley from its current track, knowing that if it continued on that track it would be derailed, killing all on board, to a spur that was safer for all on board but someone was tied across the tracks and sure to be killed if the trolley goes in that direction, what would you do?  Intentionally kill someone, or kill one to save many more?

You might think this a strange thing to consider along with the now you see it, now you don't pubic hair issue, but it's actually very similar.  The reviewer notes that the book reports research showing that what people choose to do in such a Hobson’s-choice situation is not hard-wired.  It depends upon the individual, how the choice is presented to them, their gender, and aspects of their recent lives.  They are not programmed to evaluate whether the person to be killed is one they would normally have affinity with, nor asked whether they would sacrifice themselves by jumping on the track in front of the trolley to save everyone else.  Their decision was contextual and specific to individuals. 

You might think this could be the biggest ‘so what?’ item one can imagine.  Duh!  People make different choices!  But given the tenor of the behavioral evolution literature, such optional thinking should not be optional at all: people should use their hard-wired game-theory neurons to make the self-interested decision that Darwinian selection mandated them, by eons of filtering right decisions from wrong ones, to do.

The real evolutionary problem, harder and so easily being ignored
There are countless other examples of similar issues that we could cite.  They have one aspect in common:  humans are generally not hard-wired for our behavioral repertoire.  Instead, we are hard-wired not to be hard-wired.  And how that could be is the real evolutionary problem we should be trying to understand.

 
Now you might defend the ev-psych Darwinian point of view by saying that since Eve ate the forbidden apple, it was cover-up time with the proverbial fig leaves, which thwarted the Vital View that men needed to see to know that what they wanted was ready.  Thus clothing put all bets off, and since men can't know what's hidden until the action actually starts, they now have to respond to something else, and women provide it with, say, tight clothing or makeup or hanging out in bars, or whatever.  

But that doesn't wash as an escape, because if we really were hard-wired to respond to the View, we would not be able to substitute it with something else.  For reproduction to occur and our species to survive, even clothed women would have to wear a see-through triangle (that, in freezing winter, could be double-glazed).  And women, hard-wired to be fearful that they would not be properly recognized, would never, ever, ever reach for the razor.  And of course all this male mate choice talk doesn't explain why they have pubic hair.

No, the obvious truth is that the View is not necessary--men and women can alter their landscape and still succeed.  And that raises the key point.

The hunger for competition-based, simple, dramatic and telegenic stories about how this or that behavior must have evolved to wire us to behave as we do, makes it easy to write grants, publish papers, tell stories on television and the like.  Also, it is easy, and hence convenient, to imagine and hypothesize hard-wiring of a clockwork organism, and how the trait could evolve:  if the incoming retinal signal-carrying nerve from the eye synapses in a fixed neural arc with some relevant behavioral neuron that connects with some muscle activating neurons, one can easily imagine evolution favoring this hard-wiring--when the signal comes in, the behavior goes out.  Such a generic story doesn't make a specific invocation of it true nor even easy to find the neurons, but at least it fits in a highly selection-based, model of the body as a machine.  

It sounds so simple that it sounds as if it simply must be true.  So one can see why it's easy to take this approach even when, hidden in plain sight, is the massive evidence that such pat stories are at the very best great exaggerations and usually little more than speculation. That is, one can do studies about how this particular experimental set-up or study shows what people in particular circumstances do, or how often, and even guessing at why they do it.  You can be a professor, have sage-sounding things to say, publish papers and so on.  

But it is damnably difficult to have much confidence in reconstruction of (1) the specific way, if there is one, in which genes actually affect the behavior, and (2) the evolutionary reason for it--that is, when, where, and how natural selection molded whatever the genetic basis of the trait is--if, indeed, natural selection was involved in the determinative ways usually invoked.

The real challenge
In fact, from an evolutionary and genetic point of view, the question is not whether our behavior has an evolutionary, genetic, or neural basis.  That seems rather obvious.  The challenge, and where the research ought to be being invested, is in the much more complex, longer-term, less exotic and sexy understanding of how our brains evolved not to be hard-wired.

Empirically, we use our senses and our thinking powers to evaluate circumstances in which we find ourselves, and determine how to act.  Our reasons usually seem to be quite abstract or indirect compared to simplistic Darwinian stories of immediate reproductive success.  We differ in how we assess situations, the options available, and their likely outcomes.  There is no one wiring diagram, nor one that everybody has.  Indeed, even ev-psych studies use statistical methods to argue that this or that behavior, under some controlled conditions, will occur--and statistical methods mean the behavior is, at best, only sometimes true (e.g., happens more often in some subjects shown some particular image or asked some particular questions, than in some group of controls), and at most only partially wired-in.

Instead, the real question is how can a brain be structured to do this sort of very complex evaluation and integration of many different sensory input systems, in circumstances that are always partly if not largely unique (now, to us, or to our ancestors)?  Answering that is a challenge!

If you think of it that way, you may not have the answer but you will have more respect for the difficult nature of this important biological and evolutionary problem.  You'll have more respect for science as it is supposed to be.  And you'll see that our species seems to continue to proliferate, with or without its razors.

Why we have pubic hair

A long piece in the New York Times on July 12, "Sex on Campus," by Kate Taylor, was food for thought for a number of reasons, not least because of what it tells us about the evolution of behavior. It's the tale of how, as the writer puts it, traditional sex in college has gone the way of the landline.  She interviewed a number of female students at Penn and she lets them tell much of the story themselves.  
One student says about a guy she hooks up with regularly:

“We don’t really like each other in person, sober,” she said, adding that “we literally can’t sit down and have coffee.”   

Ask her why she hasn’t had a relationship at Penn, and she won’t complain about the death of courtship or men who won’t commit. Instead, she’ll talk about “cost-benefit” analyses and the “low risk and low investment costs” of hooking up. 

“I positioned myself in college in such a way that I can’t have a meaningful romantic relationship, because I’m always busy and the people that I am interested in are always busy, too,” she said.

Until recently, it has been assumed that the "hookup culture", quick sexual encounters of whatever kind, was more satisfying to men than women.  That's because, as we all know, men want sex while women want romantic long-term relationships.  But Taylor's piece makes it clear that women are driving the current trends at least as much as men.  They talk about building their resumes and not having time for relationships.

Evolutionary psychology
The curious thing about this is how thoroughly it runs counter to what evolutionary psychology has been telling us for a long time.  Ev psych is a highly if not hyper-darwinian discipline that essentially tries to explain human behavior as the product of dictates of past natural selection that have now been built into our genomes.  For example, much of ev psych has accepted the premise that it's in females' generally, and hence human females' evolutionary interest to invest in men who will make good fathers for their children, while men never know for certain that a child is theirs and so aren't evolutionarily primed to invest in them or in relationships with their mothers.  Instead they want sex with as many women as possible, to proliferate their genes as widely as possible.  For excellent evolutionary reasons, the idea goes, men have spent eons developing strategies to avoid commitment, and women have spent the same amount of time trying to get them to commit, by hook or by crook.
 
Ev psych has churned out a multitude of theories explaining the evolutionary, adaptive basis for differences in mate choice, mate preferences, and the rates of promiscuity between the sexes. The latest amazing finding is that cunnilingus-assisted orgasm is a "sperm-retention strategy".  Will wonders never cease!

Further, the theory covers such deep theoretical questions as why we have pubic hair -- it's a sexual ornament that indicates sexual maturity and, thus, is attractive to the opposite sex.  But pubic hair itself has gone the way of the landline -- so much for sexual ornaments and indicators of sexual maturity.  It used to be that a woman's ankle could turn a man on, and that was before evolutionary psychology was even a gleam in anyone's eye, so why the field decided that what we find sexually attractive was fixed is anyone's guess.  As Taylor's piece makes abundantly clear, sexual morés are as changeable as the weather, and about as unpredictable!  It's not what we're attracted to that evolved, it's that we're attractable.

More generally, a proper critique of behavior genetics and evolutionary psychology recognizes that most of traits and behaviors they purport to explain long pre-date humans and so can't be analyzed in human-specific terms.  But more important is that if humans evolved to do anything it is to use cognition to evaluate circumstances and adjust their behavior accordingly, rather than to be hard-wired to do specific things.  What we're wired for is to have culture, but culture largely evolves on its own, not because of specific human genes.

The long history of Gay Pairee

An article in the Easter Sunday New York Times Magazine shows that homosexual behavior is found in hundreds of species of animals--even insects. That this merits an article, with lots of hand-wringing as to whether gay behavior is right or wrong, natural or otherwise, or indeed even worthy of explanation reveals a lot more about our culture than it does about nature. In short, it shows that our obsession with sexual preference is myopically ethnocentric.

Sexual preference is doubtlessly based on many genetic and environmental factors. Rather than being a rigid threshold, or a yes-no phenomenon, it is some sort of continuum that involves emotional preferences, social constraints or learning, as well as actual copulation and reproduction. This is so obvious it should not have to be discussed and trees don't need to be killed to print stories about it (of course, some of those trees might be 'homosexual'!).

The most important point is going to be the one least heeded because it threatens many vested, often fervid, beliefs about humans and evolution. That's that homosexuality is a problem that human evolutionary anthropology (as well as 'Darwinian medicine') have to explain. The problem is darwinian, or any other fundamentalism, masquerading as 'theory'. Darwinian fundamentalism assumes that what's here and organized must be so because of natural selection. No room for incidental traits, nor a wasted calorie.

From an evolutionary point of view it is no surprise of any kind that homosexual behavior would exist in other species, nor that it would have many manifestations. After all, even within humans it is like that. There is not a whiff of evidence that homosexual behavior is favored per se by natural selection, and clearly if the distribution of interactions and genital use shifted too much towards the homosexual, then it would be selected against (or some modified form of reproduction would replace the 'standard' forms--which, by the way, are themselves hugely variable).

The spectrum of sex and gender behavior, contrary to the oft-expressed shock that homosexuality could even exist (since all behaviors must be here because they're adaptive, and how could homosexuality be adaptive?), is no threat of any kind to properly understood evolutionary theory. If there were a single allele (a variant in a single gene) that inevitably conferred exclusive homosexuality upon its bearers, then our theory predicts it would disappear since if its bearers didn't engage in reproduction it could not be transmitted to the next generation. If complex genotypes confer an increased chance of gay behavior that reduced the bearers' number of offspring, it could proliferate only by chance, or by raising the reproductive success of closely related kin, though that's problematic because they, too, would carry the 'bad' gene. Theories of such 'kin selection' are elegantly mathematical but hard to prove.

On the other hand, sex-related behavior is manifestly complex, a mix of environmental, genetic, and chance effects. Given that, most 'gay' genotypes are unique--every case different, with very little net selection against any specific contributing allele. Just like other perplexing complex traits, they really aren't 'genetic' in the meaningful sense of the word, and fluidity in behaviors is simply tolerated by the weak selective constraints typical of nature.

But this kind of behavior may be interesting in its own right, if it could be stripped of the Just-So story kind of science that engages in excessive theorizing and hand-wringing, and we recognized our culture-bound reasons for even thinking it was particularly interesting. That we cling to fundamentalistic, or tribal, 'theory' is a failure of anthropology to educate scientists about themselves, or a reflection of a deep need for simple organizing principles to live by. And besides blinkered scientists, an understanding of anthropology should suffice to show that some people in a given culture, such as ours, may claim to be revolted by gay behavior but that other perfectly respectable cultures do not share that view. One doesn't have to like, or dislike, variations in sex or gender behavior to realize that such a personal view, to which everyone may have a right, is not mandated by any ultimate truths, and there's certainly no legitimate justification for religious bigotry in this respect.

An important bottom line is that this is not a human-specific problem in any evolutionary sense. The genetic permissiveness in regard to sexual preference is probably so complex that it has virtually no longterm evolutionary consequences or implications. If this is a sociobiological problem, it's hard to see how. Clearly, even in non-social species this has not happened, and homosexuality was present in early animal ancestors, so we've inherited that capability countless eons ago. It is not particularly important to species success, and not tightly monitored by natural selection.

Above all, there is no justification for human exceptionalism. To the extent that homosexual patterns are important to human society, it is not an evolutionary question but a cultural one. Its nature, variation, and impact might be interesting to study on their own, as phenomena that vary from culture to culture. If gay men help care for their brother's children it's an interesting aspect of social structure that is essentially irrelevant to the genetic aspects per se. The genetic mechanisms involved in behavioral differences might be of physiological interest, but they do not explain the phenomenon.

The same holds for many other aspects of social and behavioral traits to which human exceptionalism and lots of 'theory' have been applied. And it's why many people consider 'evolutionary psychology' to be a made-up kind of junk science, if it insists on tight 'darwinian' explanations for things for which the evidence such as discussed in the Times article shows simply isn't there. And it's time to stop geneticizing social behavior, even if, of course, genetic mechanisms are involved.

As anthropologists realized more than a century ago, social facts are best explained in terms of social facts (again, even if a minority of cases, or of behavioral extremes, have specific genetic explanations). Treating social behaviors as if they needed evolutionary explanations in the sense of Darwinian selection adds value judgments that are far more a reflection of preconceived notions of modern society (that is, of the scientists who are peering into behavior with Gotcha! hubris). Unfortunately, we know from clear and repeated history that such value judgments often provide the excuse for discrimination against people, with the upper classes deciding who's good and who's bad.

Personalized Genomics--for the investigator!

GWAS, or genomewide association studies, that claim that major common diseases are due in major part to identifiable genetic variation, have largely been discredited relative to the heavily over-hyped promises that led to its massive global funding levels. Many variants associated with studied diseases have been found, but they typically account for only a small amount of risk, even though many large studies have been done. The promise of near immortality that was made by those who would benefit from the grant largesse for GWAS has not exactly been met.

Of course, being discredited is only in the sense of its being used by the same perps as justification for even bigger and more of the same, only under a different name (e.g., biobanks and personalized genomic medicine). Those in the know know, and knew, that this kind of research was hyped from the beginning. We've discussed why in many earlier posts so won't do that now.

A recent commentary in The Economist points out these disappointing results as a dirty little secret that, the author says, will be revealed in 2010 when analysis of all the GWAS in the pipeline is completed, and it turns out they don't explain much. What then for disease genetics? The commentary doesn't really say, but it does end with a sales pitch for a different point: we'll be getting whole genome sequences on large numbers of individuals, and this will lead us to understand group (read 'race') differences. He acknowledges that this might have some negative consequences, but is basically sanguine about it.

That approval might seem curious, until you see that the author is an evolutionary psychologist. That's a field built on an insistent belief in genetic determinism, and the commentary ends with absolutely standard determinism and essentially the justification for continuing more and more DNA-based approaches to everything and anything, in this case racial differences.

The Economist is a business publication so the logic and layout of the commentary is just what you might expect: raise a specter of investment risk, but then explain why it's OK to do it in a way that the author approves of and could benefit from.

The author is correct to raise the potential for a new era of Darwinian racist determinism, a revisit to the bad days of eugenics based on new claims of group traits dressed in modern genetic technological rhetoric. But it is totally self-serving to discredit excessive genetic determinism in relation to current GWAS approaches for disease, and then credit the very same kinds of approaches to every other kind of trait.

The problem is that nobody wants to take a serious look at the issues. There can be no denying that genes affect every kind of trait, normal and otherwise. There can be no doubt that different groups of people, no matter how you define them, will have at least some differences in almost any trait: how could two groups be exactly identical in anything, after all? There will always be some traits for which any two groups you might choose will differ so substantially that not only is the average different but there is relatively little overlap (for example, skin color between Swedes and Somalis). We can't be in denial about that.

On the other hand, to suggest that whole genome sequences will have widespread use in identifying variants with important deterministic effects is simply to ignore all the GWAS evidence that we currently have, and there's a ton of it, that even though most traits have a substantial genetic contribution to their variation, most of the individual contributing variants are too weak to identify or enumerate.

One problem with evolutionary psychology is that the traits that are chosen for study are those of clear cultural interest. The problem with that is that such traits are exactly the ones on which societal discrimination has been based. To say that we'll have to learn to deal with uncomfortable truths is to say that, whether meant that way by the author or not, some races will have to face the reality that they are rather deficient in certain areas (as a group!).

That is because difference is quickly equated with importance. There is little hesitation, even though defining behavioral traits is notoriously difficult and obviously culture-loaded. Why else would race and IQ (high class behavior of certain groups that just by chance include the investigators) or sexual behavior and innate sports ability (i.e., an animalistic kind of 'talent' of some others) be the objects of study? Why not shape of lung lobes or tarsal bones, or more abstract but less socially loaded traits?

These are not new points, but humans have a history and it's a mistake to ignore it. It would be nice if we could address the real issues more seriously without political correctness or the hyped vested-interest and funding-driven predominance, or glee of the elite who dream of and would be able to afford to design their Einstein children. And it would be good also if we could face the potential for human harm if we continue to accept the idea that you are not what you eat but what you inherit. We've seen how that can loose the forces that eat at people about other people they may not like or may have to compete with, and we know where that leads.

The actual scientific issues are subtle, but are buried beneath all sorts of biases, vested interests, and self-fulfilling preconceptions.

Evolutionary psychology has had its day?

David Brooks had an interesting piece in the New York Times yesterday about evolutionary psychology. He says that evolutionary psychology has had a good run, but that it's time to recognize that organisms are much more adaptable than the field allows.

Adaptability is one of the basic principles of life that we propose in our book, but it has been out of favor in this era of genetic determinism. Genetic determinism has a long and sorry history as biological essentialism, a value-based view of what or who is good and what or who isn't, and what we really are like despite what we may think (and an assault on free will as well). It is part of a cycle in human thought....one that included decades of eugenics and Naziism as justifications for the worst possible actions by some against others.

It's interesting to see this conservative columnist taking up this cause.

How long would it take to walk to the ends of the Earth?

"Who started walking out of Africa? Not everybody walked. Very few people walked, and they walked to the ends of the Earth. The geneticists now have found that the people who migrated had a particular gene, and this gene makes you a risk-taker, a wanderer. Bipolarity is an extreme version of this gene, and the people who migrated, they had this gene."

This is a quote from Indian political economist, Deepak Lal, on the BBC radio show, The Forum, which aired 05/24/09. Lal went on to say that the people who inherited this gene for risk-taking are now ethnic minorities, which explains why they tend to "punch above their weight".

But the people who migrated out of Africa are ancestors of us all. If they had a gene 'for' risk-taking, all of us would have it, not just today's ethnic minorities. And, it can't be argued that for genetic reasons ethnic minorities tend to succeed more often than majority populations because the minorities are or were majorities somewhere at some time.

It's amazing how misguided smart people can be about genetics and population history. Granted Lal is an economist, not a population geneticist or anthropologist-- but he spoke so authoritatively! Darwinian scenarios, of the BS as well as plausible variety, are so easy to put forth with an air of confidence! But, is this all air, or does it actually matter when people get it so wrong? We suggest that it does for a number of reasons because it happens in many contexts, with ramifications, not just on BBC radio programmes.

First, the idea of a gene 'for' risk-taking has been reported, but the original study has been difficult to replicate, in part because it's difficult to define risk-taking, and in part because genes 'for' behavior have been quite elusive. Populations considered to be high risk-takers or violent by some, with a high frequency of the DRD4 mutations originally associated with risk-taking, might be considered to be pacific by others, for example. So, this trait is, like most complex traits, difficult to define and genes 'for' it difficult to confirm. If one thinks about genetic mechanisms, many genes would contribute to such traits, and they would be very culture-specific or their manifestation would be, at least.

Second, genes 'for' bipolarity, again as for all complex traits, have not been confirmed. Mapping genes making major contributions to psychiatric disorders has been very problematic, at best. Some candidates have been found, but even they generally account for only a small fraction of the instances.

Third, ethnic minorities are only such at certain times and places.

Fourth, can we really conclude that ethnic minorities are all feisty? It's funny how people with guns, money, or power can seem so much more adventurous than those who haven't the same assets.

These simple (or is it simplistic?) Darwinian arguments reflect incredibly naive population biology. Basically, nobody 'walked out of Africa' in the alleged sense. People did not have travel posters or travel agents. They might go upstream or 'over there' to find game or plants they liked to eat. If nobody was living there (or only brute Homo erectines), they might decide to kick them out and take over a nice campsite. Nobody ever heard of the ends of the earth! They did not know there were island paradises in the Pacific to go vacation at.

Young adults would pair up and move to better pastures, perhaps to get away from their annoying parents or pests in their little hunter-gatherer bands. They would, however, generally stay in touch--not go too far, because family was everything for social survival (and mates in the next generation). Gradual expansion would be on foot and in a sense by everyone, going over the next hill for open territory. Nobody would know they were going anywhere!

Each generation, village exogamy (kin-based mating rules) would mean that the 'explorers'' children would have to return to their former hearth and home to find mates. There would be large amounts of inter-village gene flow, back and forth, each generation.

It is possible that among those who chose to pop over the hill, those more inclined would have some slightly increased probability of doing that. But in the overall scheme of things, genetic drift and other kinds of chance would have watered down any such signal.

The genetic data clearly show that the farther from Africa people are, the smaller the subset of 'African' genetic variants they carry. This does not mean that they purified African adventure genes, and those in Tierra del Fuego aren't pure adventurers, nor less so than the Bantu marauders who captured each other in wars and sold the victims into slavery (unless there is an adventure gene in the slaves that made them turn themselves in?)

In historic times, and in invasions, hordes of armies or boatloads of pilgrims were forced to travel and settle elsewhere, in large numbers. They were not selected based on Indiana Jones genes.

We'll be a lot better off in evolutionary reconstructions, especially as regards behavior which clearly reflects social biases of the authors, if we temper our view based on a realistic understanding of the demographic chaos that is life!