Biological sex is amazingly complicated
December 31, 2019 10:17 AM Subscribe
It's not a binary. It's not a simple spectrum. We are spaghetti code. Lots about the biology of sex, and somewhat about the legal and social implications.
"A 46-year-old pregnant woman had visited his clinic at the Royal Melbourne Hospital in Australia to hear the results of an amniocentesis test to screen her baby's chromosomes for abnormalities. The baby was fine — but follow-up tests had revealed something astonishing about the mother. Her body was built of cells from two individuals, probably from twin embryos that had merged in her own mother's womb. And there was more. One set of cells carried two X chromosomes, the complement that typically makes a person female; the other had an X and a Y. Halfway through her fifth decade and pregnant with her third child, the woman learned for the first time that a large part of her body was chromosomally male1. “That's kind of science-fiction material for someone who just came in for an amniocentesis,” says James."
There's an audio clip in the article. Women can pick up cells from their children. Children can pick up cells from their mothers-- and from their older siblings.
Those cells can stay alive for a *long* time, and research is barely started about what effect they have.
"That the two sexes are physically different is obvious, but at the start of life, it is not. Five weeks into development, a human embryo has the potential to form both male and female anatomy. Next to the developing kidneys, two bulges known as the gonadal ridges emerge alongside two pairs of ducts, one of which can form the uterus and Fallopian tubes, and the other the male internal genital plumbing: the epididymes, vas deferentia and seminal vesicles. At six weeks, the gonad switches on the developmental pathway to become an ovary or a testis. If a testis develops, it secretes testosterone, which supports the development of the male ducts. It also makes other hormones that force the presumptive uterus and Fallopian tubes to shrink away. If the gonad becomes an ovary, it makes oestrogen, and the lack of testosterone causes the male plumbing to wither. The sex hormones also dictate the development of the external genitalia, and they come into play once more at puberty, triggering the development of secondary sexual characteristics such as breasts or facial hair."
I had the 1990's understanding that embryos start out female and being male or not. This is wrong.
"For many years, scientists believed that female development was the default programme, and that male development was actively switched on by the presence of a particular gene on the Y chromosome. In 1990, researchers made headlines when they uncovered the identity of this gene3, 4, which they called SRY. Just by itself, this gene can switch the gonad from ovarian to testicular development. For example, XX individuals who carry a fragment of the Y chromosome that contains SRY develop as males."
The social stuff at the end is mostly about intersex children being handled much more carefully than they used to be.
"A 46-year-old pregnant woman had visited his clinic at the Royal Melbourne Hospital in Australia to hear the results of an amniocentesis test to screen her baby's chromosomes for abnormalities. The baby was fine — but follow-up tests had revealed something astonishing about the mother. Her body was built of cells from two individuals, probably from twin embryos that had merged in her own mother's womb. And there was more. One set of cells carried two X chromosomes, the complement that typically makes a person female; the other had an X and a Y. Halfway through her fifth decade and pregnant with her third child, the woman learned for the first time that a large part of her body was chromosomally male1. “That's kind of science-fiction material for someone who just came in for an amniocentesis,” says James."
There's an audio clip in the article. Women can pick up cells from their children. Children can pick up cells from their mothers-- and from their older siblings.
Those cells can stay alive for a *long* time, and research is barely started about what effect they have.
"That the two sexes are physically different is obvious, but at the start of life, it is not. Five weeks into development, a human embryo has the potential to form both male and female anatomy. Next to the developing kidneys, two bulges known as the gonadal ridges emerge alongside two pairs of ducts, one of which can form the uterus and Fallopian tubes, and the other the male internal genital plumbing: the epididymes, vas deferentia and seminal vesicles. At six weeks, the gonad switches on the developmental pathway to become an ovary or a testis. If a testis develops, it secretes testosterone, which supports the development of the male ducts. It also makes other hormones that force the presumptive uterus and Fallopian tubes to shrink away. If the gonad becomes an ovary, it makes oestrogen, and the lack of testosterone causes the male plumbing to wither. The sex hormones also dictate the development of the external genitalia, and they come into play once more at puberty, triggering the development of secondary sexual characteristics such as breasts or facial hair."
I had the 1990's understanding that embryos start out female and being male or not. This is wrong.
"For many years, scientists believed that female development was the default programme, and that male development was actively switched on by the presence of a particular gene on the Y chromosome. In 1990, researchers made headlines when they uncovered the identity of this gene3, 4, which they called SRY. Just by itself, this gene can switch the gonad from ovarian to testicular development. For example, XX individuals who carry a fragment of the Y chromosome that contains SRY develop as males."
The social stuff at the end is mostly about intersex children being handled much more carefully than they used to be.
Fascinating stuff. I was astounded by how many changes were happening when I was pregnant. After a very long time of being fearful of pregnancy, I found the whole process to be a fairly wild ride. It's interesting that some cells from my daughter are likely still knocking around.
On the topic of biological sex assignment, I've long been interested in the birth order studies regarding homosexuality in men. (Two articles: Sex Redefined:
The idea of two sexes is simplistic. Biologists now think there is a wider spectrum than that and from PNAS, a commentary,
Fraternal birth order effect on sexual orientation explained.) There definitely seems to be some clues that the maternal environment can have an effect on homosexuality in males. It was this information that finally turned my mother slightly away from her theory that it was the insufferable overbearingness of her mother-in-law that was chiefly responsible for my Uncle's gayness.
posted by amanda at 2:50 PM on December 31, 2019
On the topic of biological sex assignment, I've long been interested in the birth order studies regarding homosexuality in men. (Two articles: Sex Redefined:
The idea of two sexes is simplistic. Biologists now think there is a wider spectrum than that and from PNAS, a commentary,
Fraternal birth order effect on sexual orientation explained.) There definitely seems to be some clues that the maternal environment can have an effect on homosexuality in males. It was this information that finally turned my mother slightly away from her theory that it was the insufferable overbearingness of her mother-in-law that was chiefly responsible for my Uncle's gayness.
posted by amanda at 2:50 PM on December 31, 2019
We are spaghetti code.
I feel like Their Noodliness has a role to play here...
posted by heatherlogan at 5:04 PM on December 31, 2019 [3 favorites]
I feel like Their Noodliness has a role to play here...
posted by heatherlogan at 5:04 PM on December 31, 2019 [3 favorites]
I've started posting this article in response to transphobes when they go off on how sex is binary. I tell them there will be a short quiz. They usually block me.
The think is we were badly served in being educated to think of DNA as a simple, rigid binary system. I mean nothing in our cells is rigid, life processes depend on being complex, muddy, indeterminate systems. Genetics is the same, it's a complex system that makes quantum physics look like child's play. And there are no hard boundaries, just fuzzy edges.
All of which really won't change the transphobes mind, since their major malfunction is elsewhere. But it's good for observers to know.
posted by happyroach at 1:03 PM on January 1, 2020 [5 favorites]
The think is we were badly served in being educated to think of DNA as a simple, rigid binary system. I mean nothing in our cells is rigid, life processes depend on being complex, muddy, indeterminate systems. Genetics is the same, it's a complex system that makes quantum physics look like child's play. And there are no hard boundaries, just fuzzy edges.
All of which really won't change the transphobes mind, since their major malfunction is elsewhere. But it's good for observers to know.
posted by happyroach at 1:03 PM on January 1, 2020 [5 favorites]
> I've started posting this article in response to transphobes when they go off on how sex is binary. I tell them there will be a short quiz. They usually block me.Maybe try posting this image next time, so they instantly see the information instead of having to read beyond a headline they don't like.
posted by farlukar at 8:29 AM on January 2, 2020 [5 favorites]
I'm keeping that and the OP bookmarked for next time some punkass tries to play biotruths.
posted by GoblinHoney at 1:33 PM on January 2, 2020
posted by GoblinHoney at 1:33 PM on January 2, 2020
It's even more complicated than the image farlurker posted as that doesn't even cover hermaphroditic mosaicism (that is 46XY/46XX), Klinefelter's mosaicism (47XXY/46XY and others), 47XYY syndrome or let alone the microchimerism noted in the paper or Kallmanns syndrome and prolactinomas.
We don't even know about most DSDs because the people with them never present to a doctor - even Kallmann Syndrome or large prolactinomas that suppress LH/FSH preventing puberty sometimes aren't discovered till the patient is in their 40s. Some DSDs are only really obvious on high resolution small field of view MRI eg prostatic utricles which despite their name are müllerian duct remnants that failed to regress completely, or equivalently wollfian duct remnants in otherwise female patients.
At least one expansive dsd definition I've looked at suggests that up to 2% of the population, twice as common as that stated in the paper, but even if you stick to what's known: at 1:500 male births the rate of Klinefelter's means it's as common than childhood diabetes and you'd expect 1 Klinefelter's in a high school population. (And that's for the known diagnosis rate of Klinefelter's - the real prevalence of Klinefelter's including partial mosaics is just unknown.) CAIS at 1:20000 is more common than red hair and blue eyes!
Intersex conditions and DSDs are not just not that rare - almost everyone will know someone, who will have some kind of DSD even if that person doesn't know it - possibly themselves.
posted by zeripath at 4:23 PM on January 2, 2020 [4 favorites]
We don't even know about most DSDs because the people with them never present to a doctor - even Kallmann Syndrome or large prolactinomas that suppress LH/FSH preventing puberty sometimes aren't discovered till the patient is in their 40s. Some DSDs are only really obvious on high resolution small field of view MRI eg prostatic utricles which despite their name are müllerian duct remnants that failed to regress completely, or equivalently wollfian duct remnants in otherwise female patients.
At least one expansive dsd definition I've looked at suggests that up to 2% of the population, twice as common as that stated in the paper, but even if you stick to what's known: at 1:500 male births the rate of Klinefelter's means it's as common than childhood diabetes and you'd expect 1 Klinefelter's in a high school population. (And that's for the known diagnosis rate of Klinefelter's - the real prevalence of Klinefelter's including partial mosaics is just unknown.) CAIS at 1:20000 is more common than red hair and blue eyes!
Intersex conditions and DSDs are not just not that rare - almost everyone will know someone, who will have some kind of DSD even if that person doesn't know it - possibly themselves.
posted by zeripath at 4:23 PM on January 2, 2020 [4 favorites]
This is interesting, thanks for posting! One part I hadn't heard before is that mammals seem to maintain a little bit of the ability (used commonly in some fish and other species I'm probably not familiar with) to change sex as an adult:
In 2009, researchers reported deactivating an ovarian gene called Foxl2 in adult female mice; they found that the granulosa cells that support the development of eggs transformed into Sertoli cells, which support sperm development. Two years later, a separate team showed the opposite: that inactivating a gene called Dmrt1 could turn adult testicular cells into ovarian ones.posted by clawsoon at 8:01 AM on January 5, 2020
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I tease my wife that she has our son on her mind all the time.
posted by The Power Nap at 10:26 AM on December 31, 2019 [1 favorite]