"Default Female"
Irradiated by LabRat
Since long pieces where I don’t know entirely what I’m going to put in and what I’m going to leave out don’t get along well with raid nights where the bulk of my evening is going to be devoted to geeky social things, a brief little Random Science Lesson regarding a pet peeve that got woken up and growling again today.
It’s a fairly common thing to say that all fetuses are “female by default” until they’re masculinized into boy babies by uterine exposure to testosterone. I’ve even used this phrasing myself before (though not again now that the peeve has reached full maturity) when attempting to explain how male genitals and female genitals are structures derived from the same tissues that only differentiate after that uterine hormonal exposure, which is one reason sex-change surgery has been refined so successfully for male-to-female transsexuals, at least in terms of retaining sexual pleasure. It’s also a lie-to-children- an oversimplification of the actual biology that’s useful because it’s easily graspable. It also has a point where it stops being useful, as illustrated today when I had an epic facepalm seeing this used as an assertion that femaleness is an example of neoteny.
Fetuses aren’t female until they’re masculinized, they’re neuters until they’re masculinized or feminized. It’s just that we associate maleness so completely with external sexual traits that we tend to read an apparent lack of external traits as feminine rather than as neutral. The external genitalia of a fetus that has not yet undergone sexual differentiation are neither labia and clitoris nor penis; they’re just the substrate. The tubes that will become the urinary output system, sperm delivery system, fallopian tubes, and other internal and external plumbing are still just Wolffian and Mullerian ducts and haven’t had their destiny delivered yet.
The fetus in this state isn’t female- being female requires all sorts of additional development, just stuff that isn’t visible on an ultrasound. What it actually is in biological terms is much closer to being primitive- the basic reproductive structure upon which placental mammals build in a very complex fashion but many other vertebrates barely elaborate on at all. If you’re a bird, fish, or reptile, which gender you aren’t isn’t so much a complicated anatomical statement as it is minor variation on whether the same basic tube setup delivers large gametes or small gametes. This is why it’s possible for so many fish species to be more than one sex over the course of their lives; when the only changes that need to be made are which hormones do what and whether the gametes are large or small, changing sexes as advantages change is an entirely sensible evolutionary approach. The biological definition of “male” and “female” itself, as when applied to plants and fungus and every other life form on earth that comes in two sexes, lies solely on the question of gamete size. Everything else is elaboration.
Fetuses are not “female by default”. They’re tetrapods by default.
June 30th, 2010 at 6:01 pm
I think that because they still have tails at that point, we should say that babies are puppies by default just to piss off the mommy bloggers.
June 30th, 2010 at 7:11 pm
The silliness of mammalian genitalia is evidence for the existence of the Deity, if you believe as I do that He has a very low nasty, and, yes, silly sense of humor.
Have you read Professor Grandin’s book, “Animals in Translation”? If you haven’t, read the part about the guys who breed hogs, and what they have to do to stimulate them. It’s quite funny. I’ve often wondered what happens when a boar meets a sow with a left-hand thread.
June 30th, 2010 at 8:05 pm
You have got to be shitting me.
Please say you’re pulling my leg.
June 30th, 2010 at 8:11 pm
Sadly not, Tam. Granted he was snarkily responding to some fatuous author saying something about Obama having a more feminine side and this being “evolved”, but snark or no it was… way beyond stupid.
June 30th, 2010 at 8:24 pm
Learn something new every day, go to bed a little less stupid.
Thanks for the quick lesson.
Jim
June 30th, 2010 at 9:58 pm
Good science writing!- nice synthesis of stuff I sort of knew but hadn’t ever put together.
Somehow leads to: our local Cnemidiphoruslizards, of which the majority of species seem to be all- female clones, indefinitely capable of reproducing parthenogenetically without males (some have a few male individuals, others seemingly none). Any idea how they started? Can they evolve without, say, hybridizing with outside (the species- it happens) males?
I believe also that one instance of this was recently discovered in a Komodo dragon in a zoo. I assume species with “big/ little gamete” distinctions would be more likely to do this than one with more differentiated organs- maybe only possible in such cases-??
June 30th, 2010 at 10:20 pm
Cnemidiphorus are a lovely little illustrivate case- provided you accept a certain theory of asexual versus sexual reproduction and why the one happens or the other does, and yes, it helps a great deal if the gametes and the plumbing aren’t too locked into certain paths. Grist for a post of its own, happily.
The exact plumbing details of how they started, I haven’t got, but a good theoreticla idea, sure. Proximate versus ultimate, ever so.
July 1st, 2010 at 5:20 am
I most recently saw the idea that fetuses are female by default in a claim males are mutants.
Ooh! If you post on parthenogenesis would you please discuss the varied-genome evolutionary advantage of sexual reproduction vs. the more obvious reproductive evolutionary advantage of asexual reproduction? It always used to puzzle me.
July 1st, 2010 at 7:05 am
I have been arguing against that idea since I was in high school; a quick read through something as easy as A Child is Born explains the concept quite simply, with photographs. I came across the statement that all fetuses start out female most recently from my Abnormal Psychology professor; sadly the make-up of that class was such I’ve no doubt most of them accepted it as truth.
July 1st, 2010 at 11:47 am
I’m not even going to pretend I sorta knew this: I had no idea. Thanks for the nice bit of biology
July 1st, 2010 at 4:21 pm
Mousie- I would think that, long- rage at least, that “varied genomes” would eventually trump the ease of parthenogenesis in any changing conditions, which always come. At the risk of simplifying so much I get a ruler across the knuckles from ‘Rat, that’s “why” there is sex. And also why I wonder if in these- even more blurry than usual- species that hybridization can play a useful evolutionary role. They are prone to that as well as parthenogenesis and all- female populations (which come about HOW? Because it is an easy way to occupy new territory as you imply?)
July 1st, 2010 at 5:03 pm
Hopefully I’ll have to address it tomorrow- other post in the drafting folder for today. However, Steve, I’m not only not going to rap your knuckles, I’m going to point out that the all-female parthenogenetic lines of whiptails seem to be found in predominance almost exclusively in riparian areas of the Southwest…
July 2nd, 2010 at 10:33 am
I think that because they still have tails at that point, we should say that babies are puppies by default just to piss off the mommy bloggers.
Snort, giggle, giggle. Love this comment, Phelps.
Thanks for the interesting post, LabRat, I had no idea.
*claps* I STILL remember a tiny bit of HTML markup language!