Why do women menstruate?

Menstruation is a peculiar phenomenon that women go through on a roughly monthly cycle, and it’s not immediately obvious from an evolutionary standpoint why they do it. It’s wasteful — they are throwing away a substantial amount of blood and tissue. It seems hazardous; ancestrally, in a world full of predators and disease, leaving a blood trail or filling a delicate orifice with dying tissue seems like a bad idea. And as many women can tell you, it’s uncomfortable, awkward, and sometimes debilitating. So why, evolution, why?

One assumption some people might make is that that is just the way mammalian reproduction works. This isn’t true! Most mammals do not menstruate — they do not cycle their uterine linings, but instead only build up a thickened endometrium if fertilization occurs, which looks much more efficient. Of the mammals, only most primates, a few bats, and elephant shrews are among the lucky animals that menstruate, and as you can see from the phylogeny, the scattered diversity of menstruating mammals implies that the trait was not present ancestrally — we primates acquired it relatively late.

i-58b845535df701c0ab264735f8049106-menstrual_phylogeny-thumb-500x494-71491.jpeg

Phylogeny showing the distribution of menstruation in placental mammals and the inferred states of ancestral lineages. Menstruating species/lineages are colored in pink, non- menstruating species/lineages in black. Species in which the character state is not known are not colored, and lineages of equivocal state are represented with black lines. Monodelphis represents the outgroup. Inference of ancestral states was performed in MacClade 4 by the parsimony method. Note that there is strong evidence for three independent originations of menstruation among placental mammals.

I suppose we could blame The Curse on The Fall, but then this phylogeny would suggest that Adam and Eve were part of a population of squirrel-like proto-primates living in the early Paleocene. That’s rather unbiblical, though, and what did the bats and elephant shrews do to deserve this?

There are many explanations floating around. One is that it’s a way to flush out nasty pathogens injected into the reproductive tract by ejaculating males — but that phenomenon is ubiquitous, so you have to wonder why only a few species bother. Another explanation is that it’s more efficient to get rid of the endometrium when not using it, than to maintain it indefinitely; but this is a false distinction, because other mammals don’t maintain the endometrium, they just build it up in response to fertilization. And finally, another reason is that humans have rather agressive embryos that implant deeply and intimately with the mother’s tissues, and menstruation “preconditions” the uterine lining to cope with the stress. There is, unfortunately, no evidence that menstruation provides any boost to the ‘toughness’ of the uterus at all.

A new paper by Emera, Romero, and Wagner suggests an interesting new idea. They turn the question around: menstruation isn’t the phenomenon to be explained, decidualization, the production of a thickened endometrial lining, is the key process.

All mammals prepare a specialized membrane for embryo implantation, the difference is that most mammals exhibit triggered decidualization, where the fertilized embryo itself instigates the thickening, while most primates have spontaneous decidualization (SD), which occurs even in the absence of a fertilized embryo. You can, for instance, induce menstruation in mice. By scratching the mouse endometrium, they will go through a pseudopregnancy and build up a thickened endometrial lining that will be shed when progesterone levels drop. So the reason mice don’t menstruate isn’t that they lack a mechanism for shedding the endometrial lining…it’s that they don’t build it up in the first place unless they’re actually going to use it.

So the question is, why do humans have spontaneous decidualization?

The answer that Emera suggests is entirely evolutionary, and involves maternal-fetal conflict. The mother and fetus have an adversarial relationship: mom’s best interest is to survive pregnancy to bear children again, and so her body tries to conserve resources for the long haul. The fetus, on the other hand, benefits from wresting as much from mom as it can, sometimes to the mother’s detriment. The fetus, for instance, manipulates the mother’s hormones to weaken the insulin response, so less sugar is taken up by mom’s cells, making more available for the fetus.

Within the mammals, there is variation in how deeply the fetus sinks its placental teeth into the uterus. Some species are epithelochorial; the connection is entirely superficial. Others are endotheliochorial, in which the placenta pierces the uterine epithelium. And others, the most invasive, are hemochorial, and actually breach maternal blood vessels. Humans are hemochorial. All of the mammalian species that menstruate are also hemochorial.

That’s a hint. Menstruation is a consequence of self-defense. Females build up that thickened uterine lining to protect and insulate themselves from the greedy embryo and its selfish placenta. In species with especially invasive embryos, it’s too late to wait for the moment of implantation — instead, they build up the wall pre-emptively, before and in case of fertilization. Then, if fertilization doesn’t occur, the universal process of responding to declining progesterone levels by sloughing off the lining occurs.

Bonus! Another process that goes on is that the lining of the uterus is also a sensor for fetal quality, detecting chromosomal abnormalities and allowing them to be spontaneously aborted early. There is some evidence for this: women vary in their degree of decidualization, and women with reduced decidualization have been found to become pregnant more often, but also exhibit pregnancy failure more often. So having a prepared uterus not only helps to fend off overly-aggressive fetuses, it allows mom a greater ability to be selective in which fetuses she carries to term.

The authors also have a proposed mechanism for how menstruation could have evolved, and it involves genetic assimilation. Genetic assimilation is a process which begins with an environmentally induced phenotype (in this case, decidualization in response to implantation), which is then strengthened by genetic mutations that stabilize the phenotype — phenotype first, followed by selection for the mutations that reinforce the phenotype. They make predictions from this hypothesis. In species that don’t undergo SD, embryo implantation triggers an elevation of cyclic AMP in the endometrium that causes growth of the lining. If genetic assimilation occurred, they predict that what happened in species with SD was the novel coupling of hormonal signaling to the extant activation process.

If either of these models were correct, we would expect an upregulation of cAMP- stimulating agents in response to pro- gesterone in menstruating species like humans, but not in non-menstruating species such as the mouse.

Results from experiments like those described above will elucidate the evolutionary pathway from induced to spontaneous decidualization, allowing us to answer long-unanswered questions about the evolutionary significance of menstruation. In addition, they will provide mechanistic insights that might be useful in the treatment of common reproductive disorders such as endometriosis, endometrial cancer, preeclampsia, and recurrent pregnancy loss. These disorders involve dysfunctional endometrial responses during the menstrual cycle and pregnancy. Thus, clarifying mechanisms of the normal endometrial response to maternal hormones, i.e. SD, will facilitate identification of genes with abnormal function in women with these disorders. An analysis of how SD came about in evolution can aid in identifying these critical molecular mechanisms.

Evolution, genetic assimilation, a prediction from an evolutionary hypothesis, and significant biomedical applications … that all sounds powerful to me.

Emera D, Romero R, Wagner G (2011) The evolution of menstruation: A new model for genetic assimilation: Explaining molecular origins of maternal responses to fetal invasiveness. Bioessays 34(1):26-35.

(Also on FtB)

Why do women menstruate?

Menstruation is a peculiar phenomenon that women go through on a roughly monthly cycle, and it’s not immediately obvious from an evolutionary standpoint why they do it. It’s wasteful — they are throwing away a substantial amount of blood and tissue. It seems hazardous; ancestrally, in a world full of predators and disease, leaving a blood trail or filling a delicate orifice with dying tissue seems like a bad idea. And as many women can tell you, it’s uncomfortable, awkward, and sometimes debilitating. So why, evolution, why?

One assumption some people might make is that that is just the way mammalian reproduction works. This isn’t true! Most mammals do not menstruate — they do not cycle their uterine linings, but instead only build up a thickened endometrium if fertilization occurs, which looks much more efficient. Of the mammals, only most primates, a few bats, and elephant shrews are among the lucky animals that menstruate, and as you can see from the phylogeny, the scattered diversity of menstruating mammals implies that the trait was not present ancestrally — we primates acquired it relatively late.


Phylogeny showing the distribution of menstruation in placental mammals and the inferred states of ancestral lineages. Menstruating species/lineages are colored in pink, non- menstruating species/lineages in black. Species in which the character state is not known are not colored, and lineages of equivocal state are represented with black lines. Monodelphis represents the outgroup. Inference of ancestral states was performed in MacClade 4 by the parsimony method. Note that there is strong evidence for three independent originations of menstruation among placental mammals.

I suppose we could blame The Curse on The Fall, but then this phylogeny would suggest that Adam and Eve were part of a population of squirrel-like proto-primates living in the early Paleocene. That’s rather unbiblical, though, and what did the bats and elephant shrews do to deserve this?

There are many explanations floating around. One is that it’s a way to flush out nasty pathogens injected into the reproductive tract by ejaculating males — but that phenomenon is ubiquitous, so you have to wonder why only a few species bother. Another explanation is that it’s more efficient to get rid of the endometrium when not using it, than to maintain it indefinitely; but this is a false distinction, because other mammals don’t maintain the endometrium, they just build it up in response to fertilization. And finally, another reason is that humans have rather agressive embryos that implant deeply and intimately with the mother’s tissues, and menstruation “preconditions” the uterine lining to cope with the stress. There is, unfortunately, no evidence that menstruation provides any boost to the ‘toughness’ of the uterus at all.

A new paper by Emera, Romero, and Wagner suggests an interesting new idea. They turn the question around: menstruation isn’t the phenomenon to be explained, decidualization, the production of a thickened endometrial lining, is the key process.

All mammals prepare a specialized membrane for embryo implantation, the difference is that most mammals exhibit triggered decidualization, where the fertilized embryo itself instigates the thickening, while most primates have spontaneous decidualization (SD), which occurs even in the absence of a fertilized embryo. You can, for instance, induce menstruation in mice. By scratching the mouse endometrium, they will go through a pseudopregnancy and build up a thickened endometrial lining that will be shed when progesterone levels drop. So the reason mice don’t menstruate isn’t that they lack a mechanism for shedding the endometrial lining…it’s that they don’t build it up in the first place unless they’re actually going to use it.

So the question is, why do humans have spontaneous decidualization?

The answer that Emera suggests is entirely evolutionary, and involves maternal-fetal conflict. The mother and fetus have an adversarial relationship: mom’s best interest is to survive pregnancy to bear children again, and so her body tries to conserve resources for the long haul. The fetus, on the other hand, benefits from wresting as much from mom as it can, sometimes to the mother’s detriment. The fetus, for instance, manipulates the mother’s hormones to weaken the insulin response, so less sugar is taken up by mom’s cells, making more available for the fetus.

Within the mammals, there is variation in how deeply the fetus sinks its placental teeth into the uterus. Some species are epithelochorial; the connection is entirely superficial. Others are endotheliochorial, in which the placenta pierces the uterine epithelium. And others, the most invasive, are hemochorial, and actually breach maternal blood vessels. Humans are hemochorial. All of the mammalian species that menstruate are also hemochorial.

That’s a hint. Menstruation is a consequence of self-defense. Females build up that thickened uterine lining to protect and insulate themselves from the greedy embryo and its selfish placenta. In species with especially invasive embryos, it’s too late to wait for the moment of implantation — instead, they build up the wall pre-emptively, before and in case of fertilization. Then, if fertilization doesn’t occur, the universal process of responding to declining progesterone levels by sloughing off the lining occurs.

Bonus! Another process that goes on is that the lining of the uterus is also a sensor for fetal quality, detecting chromosomal abnormalities and allowing them to be spontaneously aborted early. There is some evidence for this: women vary in their degree of decidualization, and women with reduced decidualization have been found to become pregnant more often, but also exhibit pregnancy failure more often. So having a prepared uterus not only helps to fend off overly-aggressive fetuses, it allows mom a greater ability to be selective in which fetuses she carries to term.

The authors also have a proposed mechanism for how menstruation could have evolved, and it involves genetic assimilation. Genetic assimilation is a process which begins with an environmentally induced phenotype (in this case, decidualization in response to implantation), which is then strengthened by genetic mutations that stabilize the phenotype — phenotype first, followed by selection for the mutations that reinforce the phenotype. They make predictions from this hypothesis. In species that don’t undergo SD, embryo implantation triggers an elevation of cyclic AMP in the endometrium that causes growth of the lining. If genetic assimilation occurred, they predict that what happened in species with SD was the novel coupling of hormonal signaling to the extant activation process.

If either of these models were correct, we would expect an upregulation of cAMP- stimulating agents in response to pro- gesterone in menstruating species like humans, but not in non-menstruating species such as the mouse.

Results from experiments like those described above will elucidate the evolutionary pathway from induced to spontaneous decidualization, allowing us to answer long-unanswered questions about the evolutionary significance of menstruation. In addition, they will provide mechanistic insights that might be useful in the treatment of common reproductive disorders such as endometriosis, endometrial cancer, preeclampsia, and recurrent pregnancy loss. These disorders involve dysfunctional endometrial responses during the menstrual cycle and pregnancy. Thus, clarifying mechanisms of the normal endometrial response to maternal hormones, i.e. SD, will facilitate identification of genes with abnormal function in women with these disorders. An analysis of how SD came about in evolution can aid in identifying these critical molecular mechanisms.

Evolution, genetic assimilation, a prediction from an evolutionary hypothesis, and significant biomedical applications … that all sounds powerful to me.

Emera D, Romero R, Wagner G (2011) The evolution of menstruation: A new model for genetic assimilation: Explaining molecular origins of maternal responses to fetal invasiveness. Bioessays 34(1):26-35.

(Also on Sb)

P.S. The maternal-fetal conflict is also a conflict between males and females: it is in the man’s reproductive interests to have his genes propagated in any one pregnancy, while it is in the woman’s reproductive interests to bail out and try again if conditions aren’t optimal for any one pregnancy. This conflict is also played out in culture, as well as genetics — pro-choice is a pro-woman strategy, anti-abortion is a pro-man position. Sometimes, politics is a reflection of an evolutionary struggle, too.

So I, too, could menstruate if I eat enough donuts?

Every once in a while, kind of like a cycle, some men on the internet get really mad about menstruation, and they start explaining how it’s filthy, unnatural, and disgusting for women to bleed from their vagina. “Why?” they wonder, and the obvious answer is that woman are unclean, they’re eating too much junk food, so menstruation must be their repulsive horrible body’s way of cleansing itself of toxins.

Obvs. I’m kind of curious about this “academia and the arts” cure, though, but not curious enough to wander over to the Art building on campus and ask the women faculty and students about their periods. I suspect they would, if they didn’t call the police, tell me that they’re perfectly normal and didn’t notice any decline in frequency when they entered college.

I’m also interested in this claim that “Men are the superior sex and they don’t have periods because we know how to look after their bodies.” So I could look for some fat lazy slob (why are you looking at me that way) watching trash TV (I didn’t!) and gossiping (I never!) and ask them if they’ve been menstruating lately (no, I’m not going to ask myself) (and no, I’ve never menstruated). I’m wondering if I could take up a diet of Twinkies and cheeseburgers now, and look as svelte as those ladies in the tampon commercials, if only I could start bleeding out of my bottom every month. It might be a fair trade.

It’s not just men who make these claims! Freelee the Banana Girl made similar arguments a while back. If you menstruate, you must have been wicked and accumulating toxins that your body needs to purge.

And don’t forget Yada the Hotep wackaloon. He got really angry when his daughter started menstruating, and went on a quest to find a magic bark and a magic diet that would make her stop. He also claims that animals don’t menstruate…except they sort of do. One way to stop menstruation is to get pregnant, and most mammals only thicken their endometrium seasonally, and typically don’t shed that tissue until they go into labor. Humans have the curse of year-round fertility, so that’s the problem, not that they menstruate, but that they are constantly preparing for a potential pregnancy.

I wrote about this before. It’s not about toxins or cleanses — it’s about maintaining a defensive boundary against those highly invasive mammalian embryos — put up a wall of soft vascularized tissue against the chance that you might get pregnant some month, and then discard it when fertilization fails to occur.

We can’t?

Rosie DiManno is wondering why we can’t say ‘woman’ anymore, which is a rather self-contradictory thing to declare in a big bold headline that got published in a major metropolitan newspaper. It’s also counter to common sense and every day experience, since I don’t seem to know anyone who is actually opposed to calling women women, except maybe TERFs, who are generally extraordinarily confused about just about everything to do with sex and gender. It’s a really simple concept, though!

Here’s the rule: you should address people by the identities they prefer and declare themselves. Rosie DiManno bills herself as a woman, and I am perfectly comfortable with addressing her as a woman. If I were to call her a man, I would either be hopelessly addled about who she is, or I’d be trying to insult her with a gendered insult, which is bad. So, hi Rosie, Woman, Human, Bipedal Vetebrate, etc. Strive to be respectful and accurate, is all.

Most/all of my interactions with Ms DiManno, if I were to have them, would be genderless, and there are only a few circumstances when I would have to call her a woman. “The boat is sinking, Ms DiManno — women and children to the lifeboats, you first,” perhaps, or “The ladies room is to the left, ma’am”. There are occasions when sex and gender are relevant, and you do not want to mix them up, lest you seem addled, insulting, etc.

Then there are the situations where some nuance is required, because the world isn’t the simple binary she thinks it is. She seems a bit incensed about a scientific article.

“The Lancet,” the prestigious and highly influential British medical journal, put “Bodies with Vaginas” on the cover of its latest issue, referring to an article inside, entitled “Periods on Display,” a review of an exhibit about the history of menstruation at the Vagina Museum in London.
Maybe the editors, who tweeted the piece, were just looking for clickbait, with a pullquote on the cover teasing that “Historically, the anatomy and physiology of such bodies have been neglected” — this although the author had used the phrase “bodies with vaginas,” only once and “women” four times.

But…but…there are trans men who menstruate and have vaginas. There are trans women who do not have them, and do not belong in an article about menstruation. There are cis women who do not have vaginas, and large numbers of both cis and trans women who do not menstruate. Acknowledging their existence and medical relevance is not erasing cis women at all. But Ms DiManno seems determined to erase trans men (who we call “men”, to keep it simple) and trans women (called “women”, that forbidden word in the minds of TERFs), all by inventing a totally non-existent imaginary problem.

It seems to be a common disease among right-leaning people who need imagined persecution to help them keep up their own sense of identity, so they have to create grievances. Without them, their concerns do seem to be rather petty and indefensible.

Fundraising, stories, and a new video

It’s true, we’re still digging out from under our legal debt and begging for donations. Check out our Fundraising page! There’s new stuff there!

Also, very importantly, Kris Wager is matching donations, up to a thousand dollars total. This is the perfect time to kick in a little bit to our our paypal account.

My contribution this time is a video about a science paper — a case study of an XY woman who gave birth to a child.

You can read the original paper right here, or a transcript of my remarks below the fold.

[Read more…]

An epistemological battering

Peter Boghossian has a schtick: he presents some simple, logical rules that are great for smacking down irrational claims and getting people to engage in critical thinking, and he shows how they can be applied effectively to ideas he doesn’t like. But then he pulls a switcheroo, and starts promoting his own biases, and never applies his own tools to them. It’s weird, annoying, and inconsistent, and it means I can never take him seriously. In his case, it’s obvious who shaves the barber — it’s no one, and he runs around absurdly unkempt and shaggy.

Siobhan does a marvelous and entertaining job of tearing Boghossian down. Go read that. I could just stop here, case closed, Siobhan has hammered all the high points, but I can’t help myself: Boghossian punched a few of my buttons, so I have to be all superfluous and redundant.

  1. There’s the “It’s all the Left’s fault!” mantra, which we’ve heard from the Sam Harris wing before.

    It’s fascinating. I would be lying to you if I told that I wasn’t genuinely concerned about Trump’s presidency. I think the Left bears considerable responsibility in him being elected.

    I think Boghossian would have no problem dealing with an accusation that “it’s atheists like you who make people turn to Jesus!”, but somehow he can’t recognize the inconsistency here. People who voted for Trump got him elected, not the people who didn’t vote for Trump. You could legitimately argue that poor decision-making and over-confidence by the Left contributed to Clinton’s loss, but let’s not let the people who pulled the lever for the horrible plutocrat off the hook. Do you deny them agency?

    But here’s another thing that bugs me: what side are you on? If you yourself are a left-leaning, social justice, anti-racism and misogyny type (as they all say they are), why are the complaints always phrased as “they lost the election” rather than “we lost the election”? These guys always refer to the losers in the second or third person, distancing themselves from the outcome. If you’re aligning yourself with the right wing, be confident and say so. Again, apply your reasoning to yourself. Are you willing to bear some of the responsibility for this election? What will you do in the future? Besides blaming everyone else.

  2. Then there’s his small-minded version of post-modernism.

    Disciplines such as gender studies don’t have a dialectic. They’re not truth seeking enterprises. They think they’ve already found they truth and exist to indoctrinate students. There is no dialectic at the core of those disciplines like there is in philosophy. And there are profoundly negative consequences for peoples’ views of reality — it untethers them from what’s real.

    This is so completely, utterly the reverse of the truth. Post-modernism does have a very severe dialectic, and in fact is all about dialectics, which I’ll remind Boghossian is the discipline of investigating or discussing the truth of opinions. It is actually the very heart of skepticism, although most people who call themselves skeptics are more interested in bigoted dismissal than, you know, investigating it. I’ve written about postmodernism before, so I’ll just quote Michael Bérubé here:

    Sokal’s admirers have projected almost anything they desire–and they have desired many things. In early 1997, Sokal came to the University of Illinois, and quite graciously offered to share the stage with me so that we could have a debate about the relation of postmodern philosophy to politics. It was there that I first unveiled my counterargument, namely, that the world really is divvied up into “brute fact” and “social fact,” just as philosopher John Searle says it is, but the distinction between brute fact and social fact is itself a social fact, not a brute fact, which is why the history of science is so interesting. Moreover, there are many things–like Down syndrome, as my second son has taught me–that reside squarely at the intersection between brute fact and social fact, such that new social facts (like policies of inclusion and early intervention) can help determine the brute facts of people’s lives (like their health and well-being).

    I love that counterargument. People like Boghossian like to thunder about how they know precisely what a fact is, yet never seem to recognize how strongly shaped their version of “fact” is conditioned by their social world, and never consider the possibility that social facts can represent a significant truth. Consider race, for instance. Race is scientific nonsense; people’s perception of “race” does not coincide with the patterns of descent they purport, and ought not to be used to justify the discrimination and prejudices they endorse. But at the same time, race is a social fact, and ignoring those perceptions has “profoundly negative consequences for peoples’ views of reality”. Declaring that all humans came from Africa is true, but doesn’t do a thing to negate the harsh realities of how society’s have judged humans on the basis of their skin color.

    Denying social facts, as Boghossian does, is harmful.

  3. Boghossian’s specific rant in this case is about gender, and again, he scores an own goal by failing to perceive his own social facts. In response to a quote from a transgender studies professor who rightly points out that biological sex is a complex, messy topic that doesn’t divide neatly into the boy-girl binary, he makes this ranting non-argument.

    That is the most asinine, ridiculous, preposterous piece of ideological tripe. The only way someone could possibly believe that is they’ve been sufficiently indoctrinated by radical Leftists. I was once covering a lecture for a colleague and this topic came up. I said: “If sex were really a cultural construction, why don’t men menstruate? Why don’t men have babies? Why are there no women on professional football teams?” And an individual from the back of the class got up and started yelling, “Fuck you,” gave me the middle finger, shouted at me and stormed out of class.

    That student did the right thing, and I give them credit for speaking out. Professors are supposed to be informed on a subject, and Boghossian just outed himself as an ignoramus.

    He’s a philosopher, for dog’s sake, and he just proudly created an ontological framework and declared it to be an absolute. Women are people who menstruate, have babies, and don’t play football; men are people who don’t menstruate, don’t have babies, and play football.

    Is he even aware of how intensely socially constructed his list is? Does he consider all the exceptions? He’s blitheringly oblivious. If I declared that, for example, women have long hair and men have short hair (which is not as absurd as it sounds — Americans of my parent’s generation took that as a fact), then I have just made Rachel Maddow a man and Fabio a woman. If you bounce back and rightly explain that there are multiple factors, not just one criterion, then you have admitted that the gender binary is already false. Thanks for doing my job for me.

    And if you try to play the “biological reality!” card, I’ll just point out all the exceptions to your claims that women menstruate (not all do), women have babies (childless women aren’t men), XX chromosomes (not always), and anatomy.

    Boghossian is not a biologist, yet he’s always claiming biological authority for his narrow-minded views. He’s a lot like creationists that way.

    4. Boghossian ends by citing his supporting sources, which is a good idea, but in his case, undermines everything he says. Who supports him? Dave Rubin, a right-wing pundit on youtube. Christina Hoff Sommers, anti-feminist hack and lackey of the right-wing American Enterprise Institute. Joe Rogan, misogynistic and unfunny comedian. And a Twitter account I’d never heard of before, @RealPeerReview, which is nothing but a person loudly laughing at gender studies articles they don’t understand. Some of those papers are terrible, I agree, but I seem to have frequently found papers in biology that are terrible (it’s actually not hard to do at all), and yet I don’t think all of biology is wrong, because I understand the theory and the evidence behind what I criticize. I can’t say that for Boghossian’s sources.

    Goddamn, but organized atheism has enabled a lot of cocky asswits who like to hide behind “objective reality”.

The mystery of the orgasm

Perhaps we need to think more about human psychology. There’s an interesting phenomenon that goes on all the time when people read about evolution: they shoehorn the observations into some functional purpose. There’s just something so satisfying to our minds to be able to say “that thing exists for this particular reason”, and we find it frustrating to say, “there is no reason for it, it’s just chance and circumstance”. It shouldn’t be so, but our minds just try to fit everything into that particular mold.

Now watch: some people — maybe even you — are going to now try and develop an adaptive scenario for why having brains that work that way is a good thing. We try to build a teleological framework around everything, and so it must have a purpose that is being fulfilled, and we rarely stop to think about whether it may be actually limiting us. Maybe it’s not good. Maybe there are other ways that brains can work, and this particular mode of thinking is just a clumsy kludge that resulted from the gradual agglomeration of stuff, mostly unselected, that built up the substrate for human cognition.

A case in point: the female orgasm. There’s a new paper out on the subject, and there are lots of articles being written on it, and they generally start out by pointing out that there’s something puzzling about the phenomenon: shouldn’t it have, you know, a reason for existence? It can’t just be, it has to do something useful for women, or reproduction, or pair bonding, or any of dozens of hypotheses that have been proposed.

So NPR finds closure in an explanation.

A pair of scientists have a new hypothesis about why the female orgasm exists: it might have something to do with releasing an egg to be fertilized.

Nope. That’s not what the paper says. It says it might be a relic of a historical endocrine function, not that it plays any role in women today.

Carl Zimmer sets up a mystery.

An eye is for seeing, a nose is for smelling. Many aspects of the human body have obvious purposes.

But some defy easy explanation. For biologists, few phenomena are as mysterious as the female orgasm.

I would challenge his analogy: what’s so obvious about a nose? Nostrils and an olfactory epithelium, sure — that does have a clear functional role, and we can see signs of selection in the signal transduction apparatus, but why do we have this bony projection with a knob of cartilage on the end? We think we’d look weird without it (like Voldemort), but there’s a wide range of shapes within our species, and related species — chimps and gorillas, for instance — don’t have much in the way of a nose. It doesn’t affect their ability to smell.

(Note: both of those links take you to good summaries. I’m just weirdly conscious of how much we all take adaptive thinking for granted.)

This is the point where I tell you all to go read The Case of the Female Orgasm: Bias in the Science of Evolution by Elisabeth Lloyd, in which she takes apart a collection of adaptive scenarios that simply do not hold up. We ought to face facts: orgasm in women has nothing at all to do with reproduction. It doesn’t facilitate transport of semen, it doesn’t make them want to lie down horizontally, it doesn’t compel them to pair bond with men (since masturbation is a more effective path to orgasm than intercourse, why aren’t we arguing that the clitoris is the devil’s tool to drive women away from men? Oh, some do.)

Fortunately, this new paper by Pavlicev and Wagner, The Evolutionary Origin of Female Orgasm, doesn’t succumb to the fallacy of the spurious adaptive explanation. Instead, it’s following a much more useful evolutionary tradition: everything is the way it is because of how it got that way. Every living thing has a line of ancestry, and we inherit with modification the traits of our lineage, and the necessary way to study these traits, since our ancestors aren’t generally available for examination, is to take a comparative approach. So they do the evolutionary biology thing and ask what functions female orgasm have in related species, and try to infer an ancestral role in pre-humans.

Here, we note that most hypotheses are seeking an explanation for the presence of female orgasm within the human or primate lineage, whether due to direct or correlated effects of selection. Yet we will argue below that female orgasm, as male orgasm, predate the primate lineage, and the orgasm of human females likely evolved from an ancestral and adaptive trait, which might not have all the characteristics of human orgasm and may also have had a different function. We propose that explanations focusing on primate mating system and behavior thus address the primate-specific (or sometimes human-specific) modifications of a previously existent trait rather than its origin (Amundson, 2008). Our focus here will be the question what that ancestral trait may have been. As the lineage-specific modifications or secondary cooption (“exaptation,” in terms of Gould and Vrba, 1982) can take extreme forms under different, internal, or external selective forces, we therefore do not expect to find in animals a female orgasm as we know it in human, but are rather seeking its homologue in other species.

They also place it in the context of more general theories about the basis of the female orgasm.

The field addressing the role of female orgasm is by no means short of hypotheses. The evolutionary hypotheses align in two groups: one group argues that it is not quite true that female orgasm has no effect on reproductive success (e.g., enabling female choice, bonding, etc.), and the other group argues that it may indeed have no reproductive value in the females, but rather its existence is explained as a correlated effect of another selected trait, or a different developmental stage. For example, one well appreciated among the later hypotheses describes female orgasm as a fortunate consequence of the shared developmental basis of clitoris and penis, and therefore a consequence of reproductive necessity of the male orgasm (by-product hypothesis, Symons, 1979). A critical review of the existing hypotheses has been published in Lloyd (2005) and will not be attempted here.

So the two general hypotheses are that it has an as-yet-undetermined reproductive function (this is so far unsupported by the evidence), or that it is a byproduct of other properties. Pavlicev and Wagner are, I think, adding some other nuances to the story, but their explanation is actually orthogonal to those two explanations.

Pavlicev and Wagner point out that induced ovulation is common in mammals, and is probably a basal trait of the clade, although it has been repeatedly gained and lost. It’s an energy saving measure; why should the female spontaneously ovulate all the time, in the absence of an opportunity to become pregnant? We take it for granted — nuns continue to menstruate, after all — but many mammals do not ovulate unless they receive an endocrine signal that announces to their ovaries that hey, you’re actually mating, this might be a good time to drop an egg for fertilization. In these species, the clitoris seems to be the trigger — stimulating it induces an endocrine surge that induces ovulation. So the idea is that humans have female orgasms because our distant mammalian ancestors had all this complex hormonal machinery coupling ovulation and coitus, and we’ve lost the necessity, but the apparatus is still there. We’ve dismantled the factory, but the remnants still make a fine playground.

Another interesting pattern they see is that when ovulation is uncoupled from clitoral stimulation, there is a tendency for the clitoris to waner farther from the vaginal opening. Induced ovulators tend to have the clitoris positioned right near or even within the vaginal opening, but in animals like humans, it’s quite far away and is poorly stimulated by vaginal thrusting. This may be another of those byproducts: the opening of the urethra happens to be between the vagina and the clitoris, so the increasing separation of the clitoris and vagina may be a consequence of increasing the separation of the urethra and vagina.

I do have some slight reservations about the paper, though. One is that the explanation is insufficient. Here’s their diagram of the phylogenetic distribution of induced ovulation.

Phylogenetic distribution of (A) modes of ovulation, (B) the presence of the urogenital sinus (UGS; in basal species: cloaca), and (C) the position of clitoris relative to the vaginal orifice (in, border, out). Note the phylogenetic correlation between spontaneous ovulation with the reduction of the urogenital sinus, and the external position of the clitoris. This correlation is suggestive of an ancestral role of clitoral stimulation for the initiation of pregnancy in induced ovulators and the loss of this function in spontaneous ovulators.

Phylogenetic distribution of (A) modes of ovulation, (B) the presence of the urogenital sinus (UGS; in basal species: cloaca), and (C) the position of clitoris relative to the vaginal orifice (in, border, out). Note the phylogenetic correlation between spontaneous ovulation with the reduction of the urogenital sinus, and the external position of the clitoris. This correlation is suggestive of an ancestral role of clitoral stimulation for the initiation of pregnancy in induced ovulators and the loss of this function in spontaneous ovulators.

Note that our lineage seems to have lost this property at the separation of rodents and primates! One estimate is that this divergence occurred about 96 million years ago, so our ancestors had to have lost the requirement to link clitoral stimulation to reproduction deep in the Cretaceous, yet still maintained the association between clitoral stimulation and orgasm to the modern day.

That retention is still best explained by the byproduct hypothesis — the pleasure circuitry is maintained by ongoing selection for its operation in males, and there’s no purpose to untangling it and removing it from females, and in fact, selecting for anorgasmia in females might have unfortunate reproductive side effects in males.

I’d also suggest that it doesn’t answer another question: why does sex feel good? We have other urges that our physiology doesn’t address by inducing super-charged sensations — I mean, why don’t we have wild orgasms every time we urinate? Why doesn’t my thyroid send ripples of joy through my body when I balance my salt intake? If you’ve ever watched cats mating, you also know that sex for them is more a matter of compulsion than an opportunity to revel in pleasurable sensations by choice. Do salmon enjoy thrashing themselves to death? I might also argue that to some human males sex isn’t a matter so much of feeling good as it is conquest, expressing dominance, and flaunting their social potency to their peers, so there are clearly alternative mechanisms to make sure males mate with females.

I might suggest that the mystery isn’t the female orgasm, but the orgasm, period. But it’s only a mystery if you insist on demanding a direct adaptive explanation for its existence.

An atheist can be pro-life only by lying about the science

Hemant Mehta let an anti-choice atheist romp about and make her secular pro-life argument, but since he thinks it’s important to give a forum to bullshit but doesn’t think it’s important enough to criticize, I guess I have to. It’s by Kristine Kruszelnicki, president of Pro-Life Humanist, and we’ve dealt with her before; she’s the one who debated Matt Dillahunty in 2012, and lost miserably. She acknowledges that right at the beginning of her post, and then proceeds to make the same stupid argument.

Before we address the question of bodily autonomy in pregnancy, let’s meet the second player. What does science tell us that the preborn are? To be clear, science doesn’t define personhood. It never could. When I debated Matt Dillahunty on the issue of abortion at the 2012 Texas Freethought Convention, I’m afraid that as a first-time debater I really wasn’t clear enough on this point — and was consequently accused of trying to obtain rights from science. Science can’t tell us whether it’s wrong to rape women, torture children, enslave black people, or which physical traits should or should not matter when it comes to determining personhood. Science may be able to measure suffering in living creatures, but it can’t tell us why or if their suffering should matter.

Notice what she’s doing here. She recognizes that she totally got skewered on her claim that Science says abortion is wrong, so she’s nominally distancing herself from making moral claims with science. But guess what her very next sentence is?

However, science can tell us who among us belongs to the human species.

She’s doing it again. She’s claiming that science justifies her position.

She is at least aware that the right of women to autonomy is an extremely strong argument against her position — it’s how Dillahunty slammed her in the debate — and the entire post is about how she gets around that tricky problem of denying women control of their own bodies. Her solution? Simply decree by fiat, with the stamp of approval of her version of science, that the fetus and the woman have fully equal status as human beings, and that all discussion has to grant the fetus every privilege we do the woman.

If the fetus is not a human being with his/her own bodily rights, it’s true that infringing on a woman’s body by placing restrictions on her medical options is always a gross injustice and a violation. On the other hand, if we are talking about two human beings who should each be entitled to their own bodily rights, in the unique situation that is pregnancy, we aren’t justified in following the route of might-makes-right simply because we can.

At least this time, she didn’t sprinkle photos of bloody fetus parts in her post, and she avoided the most egregiously absurd elements of her position. This is my summary of what she said at the debate:

She made it clear that she opposes a whole gamut of basic rights: birth control methods that prevent implantation are wrong, because that’s just like strangling or starving a baby; no abortion in cases of rape or incest, because the baby doesn’t deserve punishment; she did allow for abortion in cases that threaten the life of the mother at times before fetal viability, simply because in that case two fully human lives would be lost.

She sounds like a very liberal Catholic atheist.

But that’s the entirety of her argument, both in that piece and on the pro-life atheist web site: the fetus is fully human from the moment of conception, and science says so.

When it comes to normal human reproduction, sperm and ovum merge to form a new whole. They cease to exist individually and become a new substance that is not the mother and not the father but a new body altogether, one that is also human and has the inherent capacity to develop through all stages of development.

When we talk about rights and personhood, we leave the realm of science for that of philosophy and ethics. History is ripe with examples of real biological human beings whose societies arbitrarily decided they didn’t qualify as equals, on account of criteria deemed morally relevant. At one point (and still, in many ways, today), it was skin color, gender, and ethnic background. Now, we can add to that list consciousness, sentience, and viability. We haven’t evolved so fast in 50 years as to be immune from tribalistic us vs. them thinking. If science defines a fetus as a biological member of our species, is it possible that our society is just as wrong in denying them personhood?

What happens when both a woman and her developing fetus are regarded as human beings entitled to personhood and bodily rights? Any way you cut it, their rights are always going to conflict (at least until womb transfers become a reality). So what’s the reasonable response? It could start by treating both parties at conflict as if they were equal human beings.

You get the idea. If she repeats that the conceptus becomes fully human at the instant of fertilization, and that science says so, over and over, we surely must be persuaded that she’s right, and we have to concede that she’s making an entirely secular argument, because SCIENCE. Unfortunately for her, she’s not actually using SCIENCE, but has mistaken BULLSHIT for science.

Let me tell you what science actually says about this subject.

Science has determined that development is a process of epigenesis; that is, that it involves a progressive unfolding and emergence of new attributes, not present at conception, that manifest gradually by interactions within the field of developing cells and with the external environment. The conceptus is not equal to the adult. It is not a preformed human requiring only time and growth to adulthood; developmental biologists are entirely aware of the distinction between proliferation and growth, and differentiation. So science actually says the opposite of what Kruszelnicki claims. It says that the fetus is distinct from the adult.

Of course, science also has to concede that because there is a continuum of transformation from conception to adulthood, it can’t draw an arbitrary line and say that at Time Point X, the fetus has acquired enough of the properties of the adult form that it should be now regarded as having all the rights of a member of society. That’s a matter for law and convention. But we already implicitly recognize that there is a pattern of change over time; children do not have all the same privileges as adults. Third trimester fetuses have fewer still. First trimester embryos? Even less. We all understand without even thinking about it that there is a progressive pattern to human development.

But what about this claim that science can tell us who among us belongs to the human species?

First question I have is…which species concept are you using? There are a lot of them, you know; I daresay we might be able to find a few, that when inappropriately and too literally applied, would define away my status as a human, which simply wouldn’t do. There are also a lot of non-scientific or pseudo-scientific definitions of what constitutes a human that have been historically abused. Were the Nazis being scientific when they defined sub-species of humans and classed Jews, Gypsies, and Africans as something less than fully human? What, exactly, is Kruszelnicki’s “scientific” definition of human, that she’s using so definitively to declare a fetus as completely human?

She doesn’t say. She can’t say. She’s not applying a scientific test, but a traditional and colloquial one, which she’s then claiming by implication as synonymous with an unstated scientific definition. That’s dishonest and more than a little annoying.

Reading between the lines on her horrible little website, I’m guessing that she’s using a trivial and excessively reductive definition of human: it’s human by descent. The cells come from the division of human cells, so it is by definition not a monkey or a llama or a beetle cell, it’s a human cell.

Of course, that’s not enough: by that definition, sperm and eggs would be fully human, and women would be committing murder every time they menstruate, and men would be committing genocide every time they ejaculate. So she has a patch to work around that:

There is no such species as “sperm” or “ovum”. Sperm and ovum are not distinct unique organisms. They are in fact complex specialized cells belonging to the larger organism, namely the male and female from which they came. In other words, they are, like skin cells and blood cells, alive and bearing human DNA but nonetheless parts of another human being, even when mobile like the sperm.

There is no such species as “man” or “woman” either; we can always find some characteristic of an individual to distinguish them from a species (well hey, just the fact that they are an individual is enough). Her waffling about the status of sperm and ovum is ridiculous; I can give you species definitions that would recognize haploid gametes as fully human. If your restriction is simply that one is a complex, specialized cell belonging to the larger organism, well gosh, the zygote fits that, too! A fertilized egg is not a generic human cell: it is incredibly specialized and complex.

I can’t help but notice that multicellularity isn’t part of her definition of “human”. Nor does it include any craniate characters, like having a notochord or a brain or branchial arches. There are a lot of scientific definitions of our species that the zygote fails!

If we’re going to emphasize the “not part of a human being” aspect of her fuzzy definition, then we have another problem. If you pooped this morning, that turd contained shed human epithelial cells, now swimming free. I could actually say, with full scientific accuracy, that that was a human turd. Why aren’t you giving it full legal protection?

She has an escape clause for that, too.

Sperm and ovum lose their individual identity and their function as sperm and ovum once they have merged. Instead of being parts carrying 23 chromosomes from two different human beings, the unification and merging of their chromosome pairs has now created a new whole with a new set of chromosomes and a cellular structure that now contains the inherent capacity to grow and develop itself through all stages of human development. This of course is something that neither sperm nor ovum parts had the inherent capacity to do on their own. It’s something that only whole human beings can do.

Oh. So here’s her full definition of a fully human being: it is a totipotent cell with the capacity to develop into a human being. Alas, her last sentence is wrong. Whole human beings cannot do that. It means I am not human, only a few small bits of me can aspire (in vain! I’m done with that) to someday fuse with another haploid cell and briefly become fully human, in the few days of happy cleavage before their cells become committed to specialized fates, which then are not fully human.

The only logical scientific conclusion one can make from Kruszelnicki’s hopeless definition is that blastocysts are fully human, but people are not.

Which actually doesn’t surprise me at all, and fits quite well with what I hear from the fetus-worshippers.

As I said before, there certainly are secular arguments for all kinds of nonsense — “secular” is not a synonym for “good”. We have to do more than simply accept arguments because they don’t mention gods, we also have to apply logical, reasonable philosophical and scientific filters to those secular arguments. The one obvious conclusion from any examination of these so-called “pro-life” arguments is that they are sloppy and dishonest, and not deserving of recognition by reasonable secular people.

Being atheist is not enough. One of the implications of an absence of gods is that revelation is invalid, and that we have to rely on reason and evidence to draw conclusions…and further, I would add, that we have to define values that we consistently and rationally apply, and we have to assess whether our methods appropriately serve those values. I choose to value the equality of a community of living, fully-born human beings, and when irrational superstitious attachment to status of a blastocyst compromises the autonomy and worth of members of that community, I choose to reject that belief. It helps quite a bit, though, that the “pro-life” position is so incoherent and anti-scientific.

Another take: even if you accept Kruszelnicki’s premise that a conceptus is “fully human” (I don’t), her argument doesn’t work and was dismantled over 40 years ago.