Why Vaginas?

November 25, 2015 12:42 PM

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's quite a lot of work on how penises and testicles evolve (previously!), but comparatively little work is done on vaginas or ovaries. Hell, we didn't even have a thorough anatomical description of the human clitoris until 1998. It's not as if vaginas aren't as weird and wonderful as penises, either--just ask a duck. Of course, strictly speaking female ducks don't have vaginas like mammals do--that's because a dedicated reproduction-only anatomical channel is something only mammals bother with. (Reptiles, frogs and birds just use one cloaca for reproduction and excretion. We have no idea why mammals do things differently.) Ignoring vaginas is handicapping the study of evolution for no good reason.

posted by sciatrix (45 comments total)

unless the size and shape of the human vagina has an exceptional story

Oh, if those vaginas could talk, what tales they would tell!
posted by GenjiandProust at 1:04 PM on November 25, 2015 [8 favorites]

(Reptiles, frogs and birds just use one cloaca for reproduction and excretion. We have no idea why mammals do things differently.)

I'm probably showing my ignorance more than anything here, but I always just assumed this was because of live birth contra egg-laying...
posted by Dysk at 1:10 PM on November 25, 2015 [2 favorites]

So what she's saying is, women went first in the size-a-thon and men had to step up their game to have reproductive success.

And if you think about it, the bigger birth canal had to come first; otherwise you have a baby that can't be born because its mother was too small. So women who had more room, could have bigger-headed babies, who were smarter*, and they had more reproductive success and then men had to likewise adjust.

*I assume? Although given the intelligence of beings like crows, I've always wondered how close the correlation is
posted by emjaybee at 1:11 PM on November 25, 2015 [2 favorites]

I'm probably showing my ignorance more than anything here, but I always just assumed this was because of live birth contra egg-laying...

This feels like it should be right. After all, it's all egg-layers, including monotremes, that have cloacas. But correlation is not causation and all that...
posted by howfar at 1:15 PM on November 25, 2015 [1 favorite]

I mean, a newborn and a cloacal tract that's regularly used for excrement sounds like infection city to me...
posted by Dysk at 1:16 PM on November 25, 2015 [1 favorite]

More seriously, if nothing else, this is a great addition to the "science may not be biased, but scientists sure are" pile.
posted by GenjiandProust at 1:16 PM on November 25, 2015 [36 favorites]

I always just assumed this was because of live birth contra egg-laying

In order to successfully study this we need babies inside eggs. someone put a baby in an egg for science.
posted by poffin boffin at 1:18 PM on November 25, 2015 [17 favorites]

After all, it's all egg-layers, including monotremes, that have cloacas.

I think I read somewhere that egg-layers also have huge variation in the size of the egg vs the size of the mother, topping out with kiwi eggs being nearly a quarter the size of their bird laying them. I assume with a more complex birth anatomy, no female kiwi would survive giving birth.

Although that is also a "chicken and egg" situation.
posted by GenjiandProust at 1:19 PM on November 25, 2015 [1 favorite]

In order to successfully study this we need babies inside eggs. someone put a baby in an egg for science.

Dejah and I will get right on this.
posted by The Tensor at 1:21 PM on November 25, 2015 [7 favorites]

Let me just add, this is that rare exception that warrants reading the comments. They are good and thoughtful and add to the overall discussion of the topic.
posted by mosk at 1:25 PM on November 25, 2015 [4 favorites]

[more inside]
posted by emelenjr at 1:37 PM on November 25, 2015 [32 favorites]

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...

My Thanksgiving's going to be tense enough already, thank you very much.
posted by PlusDistance at 1:59 PM on November 25, 2015 [4 favorites]

Oh, if those vaginas could talk, what tales they would tell!

Previously.
posted by Pater Aletheias at 2:00 PM on November 25, 2015

Great article. One of the commenters makes the excellent point that it's perfectly possible that the human penis didn't directly evolve at all, not even in response to the growing vagina problem - the selection pressure on the vagina to be large enough to safely accommodate big smart baby heads may have affected developmental processes that also affect the size of the penis (since they are the same structures). So all the just-so stories about the benefits and utility of larger penises are quite possibly completely irrelevant.

Hilarious.
posted by misfish at 2:02 PM on November 25, 2015 [20 favorites]

baby in egg
posted by nzero at 2:02 PM on November 25, 2015

My Thanksgiving's going to be tense enough already, thank you very much.

Though if your uncle starts talking about how Donald Trump would know what to do about Caitlyn Jenner, beginning to talk about penis bones and vaginas vs cloacas might buy you enough time to jump out the window.
posted by happyroach at 2:23 PM on November 25, 2015 [19 favorites]

In order to successfully study this we need babies inside eggs. someone put a baby in an egg for science.

The pioneering science of Anne Geddes.
posted by klangklangston at 2:25 PM on November 25, 2015 [14 favorites]

The pioneering science of Anne Geddes.

This should be a horror movie poster. That is one sinister-looking baby.
posted by curious nu at 2:43 PM on November 25, 2015 [8 favorites]

Ooh, I wrote a long paper last year on the apparent lack of estrus in humans (estrus being a period in which the anogenital area of a female primate will swell, basically advertising her fertility to males). I came across a lot of research on vaginas, and there is some really interesting work - although until not too long ago a lot of it did seem to conform to prevailing attitudes towards women. I didn't study the vagina from this angle, though, so this is interesting. Thanks for posting it!

Also, if you're curious - at least as best as I can tell from the research out there, we don't really know for sure why humans don't have fertility signals, or if they do and it's more of a "hidden estrus" period (that's more or less what that whole "ovulating women get better tips" thing from a few years ago was about). In fact, it's not even totally clear that human ancestors ever had any kinds of fertility signals; it may be that other primates evolved the trait after divergence with our last common ancestor (this includes some criticisms of comparing human sexuality with that of bonobos - interesting stuff).

I can't find my paper now, but I do remember coming across some really interesting research on, basically, what could have influenced early hominid sexuality, and how our bodies and behaviors may have adapted as a result. Will track down and write more if anyone is interested.
posted by teponaztli at 2:43 PM on November 25, 2015 [7 favorites]

This should be a horror movie poster. That is one sinister-looking baby.

That would be a great poster for a film about David Icke-style reptilians, Among Us.
posted by atoxyl at 2:51 PM on November 25, 2015 [1 favorite]

The slime effects need work though - can we get Rob Bottin?
posted by atoxyl at 2:56 PM on November 25, 2015

I do actually wonder sort of unreasonably often if oviparous human reproduction would bring a greater gender balance to childbirth/child rearing but it is hard for me to tell how much is legitimate scientific inquiry and how much is wanting to convince men to carefully sit on large eggs.
posted by poffin boffin at 3:17 PM on November 25, 2015 [25 favorites]

Oh, if those vaginas could talk, what tales they would tell!

My least favourite William Burroughs story.
posted by GuyZero at 3:44 PM on November 25, 2015 [9 favorites]

(Reptiles, frogs and birds just use one cloaca for reproduction and excretion. We have no idea why mammals do things differently.)

I'm probably showing my ignorance more than anything here, but I always just assumed this was because of live birth contra egg-laying...

Tell that to the marsupials.
posted by HiroProtagonist at 3:53 PM on November 25, 2015 [1 favorite]

Yikes, sorry if my tone was too light or my substance not on the mark with my first (deleted) comment attempt. The thesis of the main FPP seems spot on (that it was the reproductive need for a wide birth canal that made penises larger, not sexual selection) and the point about men being obsessed with their penises and that driving the science is a good one, too. Apologies if my first attempt to praise the post came out too unserious or tone deaf. I'm (sincerely) fascinated by the biological complexity of vaginas. Either way, great post.
posted by saulgoodman at 3:57 PM on November 25, 2015

The selection pressure on the vagina to be large enough to safely accommodate big smart baby heads may have affected developmental processes that also affect the size of the penis (since they are the same structures).

oh joy sex toy just did a great strip on this.

Also, if you're curious - at least as best as I can tell from the research out there, we don't really know for sure why humans don't have fertility signals, or if they do and it's more of a "hidden estrus" period

there's also just so much variation in how people who ovulate do so. in groups where i've discussed it i've found that my body is far more outward about the whole process than a lot of people. i get mttelschmerz, my boobs swell, my nipples get tender, my vuvla swells and produces a lot more discharge. i'm pretty sure my husband can tell i'm ovulating just by touch. now, i'm not saying it's like a primate, but i do think variation is something that is ignored somewhat because female bodies are so understudied.
posted by nadawi at 4:01 PM on November 25, 2015 [16 favorites]

bigger-headed babies, who were smarter*

*I assume? Although given the intelligence of beings like crows, I've always wondered how close the correlation is

Bigger brains could be one route to greater intelligence without being the only route.
posted by straight at 4:04 PM on November 25, 2015 [4 favorites]

Oook oook.
posted by mikelieman at 4:22 PM on November 25, 2015 [1 favorite]

I'm probably showing my ignorance more than anything here, but I always just assumed this was because of live birth contra egg-laying...

Tell that to the marsupials.

Far as I can make out from wikipedia, marsupials have both a dedicated reproductive tract and (platypus aside) don't lay eggs. So I'm telling marsupials what, again?

I cannot find anything on a quick glance at wikipedia to say whether or not platypuses have vaginas, though I have now learned that they incubate the egg mostly internally, laying it only about 10 days before hatching
posted by Dysk at 4:39 PM on November 25, 2015 [2 favorites]

<sub>platypuses and echnidnas aren't marsupials, they're monotremes

by the way they also don't have a single set of XY chromosomes with a master sex-determining SRY gene like all other mammals, they have a set of five overlapping pairs of sex chromosomes such that a male platypus has a XXXXX YYYYY karyotype

also kangaroos have a trifold vagina and the joey and sperm don't even go the same way so something weird is going on there</sub>
posted by sciatrix at 4:45 PM on November 25, 2015 [25 favorites]

_{there's not really a point to that comment I'm just a huge nerd about this}
posted by sciatrix at 4:45 PM on November 25, 2015 [21 favorites]

That kangaroo vagina is awesome. Lots of weird stuff going on there -- three vaginas (to go with a two-pronged penis)! Two uteruses!

I am so glad I am not a kangaroo.
posted by jeather at 4:50 PM on November 25, 2015 [5 favorites]

I mean, a newborn and a cloacal tract that's regularly used for excrement sounds like infection city to me...

It's not as if they're hermetically separated in humans, in general or during birth. Believe me (a home birther of the 'it was just me, the missus, and the midwife when the Entonox ran out' school writes) , there ain't nothing antiseptic happening. Blood, shit, mucus, what-the-fuck-is-THAT... all come to the party.

And yet, here we all are.
posted by Devonian at 4:59 PM on November 25, 2015 [10 favorites]

It's probably also worth mentioning that there's species like snakes which are live-bearing like mammals while also using a cloaca, so it's probably not JUST about eggs vs livebearing offspring.
posted by sciatrix at 5:24 PM on November 25, 2015 [1 favorite]

That's a really fascinating article. I'd also go so far to say the differences between vaginas is probably poorly understood as well, so we say "large vagina to deliver the baby" buts what's the typical size across the range of "large"?

(A lot to think about and one more reason why I'm not too keen on getting my junk tampered with as part of my own process.)
posted by Annika Cicada at 5:40 PM on November 25, 2015 [3 favorites]

Oh, if those vaginas could talk, what tales they would tell!

Denis Diderot was already on it in 1748.
posted by thomas j wise at 5:57 PM on November 25, 2015 [1 favorite]

Oh, if those vaginas could talk, what tales they would tell!

And in 1977 they made a movie about it.
posted by jonp72 at 7:12 PM on November 25, 2015 [1 favorite]

I do actually wonder sort of unreasonably often if oviparous human reproduction would bring a greater gender balance to childbirth/child rearing …

There's a drug for that.

Cloaxia: Cloacas for women!
posted by wemayfreeze at 7:23 PM on November 25, 2015 [1 favorite]

Superb post, and nthing the suggestion to - this time - read the unusually thoughful, insightful and interesting comments thread attached.

Especially this one from the OP author: And I've decided that if I write an expanded version of this for publication I will title it something like, "The Evolution of Man's Vagina".

I... very much hope that she does write an expanded version for publication, and titles it so.
posted by motty at 7:32 PM on November 25, 2015 [8 favorites]

Humans don't have obvious signals of estrus

I saw a report of a recent study that showed that strippers made a lot more in tips when they were in the most fertile part of their menstrual cycle. So it would seem that human females have subtle signals of estrus. (Cue: just-so story explaining why this is so. )
posted by monotreme at 9:00 PM on November 25, 2015

posted by monotreme

Well I for one admire your restraint. Other, less saintly commenters would be all up in here with a WHAT UP GUYS DID SOMEONE SAY CLOACA, but no. Commendable.
posted by Jon Mitchell at 10:48 PM on November 25, 2015 [4 favorites]

Strippers don't make more money during ovulation
posted by benzenedream at 11:16 PM on November 25, 2015 [5 favorites]

Oh, if those vaginas could talk, what tales they would tell!

Talking is just a set of teeth away from being vagina dentata, which would change all kinds of interpersonal dynamics.
posted by Dip Flash at 11:25 PM on November 25, 2015

"Ooh, I wrote a long paper last year on the apparent lack of estrus in humans (estrus being a period in which the anogenital area of a female primate will swell, basically advertising her fertility to males). I came across a lot of research on vaginas, and there is some really interesting work - although until not too long ago a lot of it did seem to conform to prevailing attitudes towards women. I didn't study the vagina from this angle, though, so this is interesting. Thanks for posting it!"

Weirdly, my facebook feed has been full of scientific discussions of the origins of menstruation this week, and the lack of estrus has been a tangent to that. The shape of vagina was a tangent too, mostly because one of the arguments is that menstruation is a way of protecting women from some of the costs of pregnancy when the child or mother would be less likely to survive, and so notionally similar to the ducks preventing lesser-fit offspring.

"Vaginas talking would also change all kinds of interpersonal dynamics. Who knows, they might be great conversationalists."

I would assume they'd be as good or poor conversationalists as the woman herself. It's not like mouths are better or worse conversationalists than the women who have them.
posted by klangklangston at 1:48 PM on November 26, 2015

it is hard for me to tell how much is legitimate scientific inquiry and how much is wanting to convince men to carefully sit on large eggs

See also: Geisel, T. Horton Hatches the Egg. New York: Random House, 1940.
posted by flabdablet at 11:08 PM on November 26, 2015