sperm race myth

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Stephanie
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sperm race myth

Post by Stephanie » Sun Dec 27, 2020 9:33 am

Fascinating article on reproduction. First time I'd heard of crypts for storing sperm

https://aeon.co/amp/essays/the-idea-tha ... macho-myth
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Allo V Psycho
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Re: sperm race myth

Post by Allo V Psycho » Sun Jan 03, 2021 12:52 pm

Stephanie wrote:
Sun Dec 27, 2020 9:33 am
Fascinating article on reproduction. First time I'd heard of crypts for storing sperm

https://aeon.co/amp/essays/the-idea-tha ... macho-myth
Well, I dunno. I don’t want to attack colleagues of different disciplines, but I wouldn’t choose an anthropologist as my first line of resource for human reproduction info. Sometimes someone from a different discipline is narrowly rather than widely read.

I think he gets confused between sperm competition between males, which is well attested in some species, and sperm competition between sperm from one individual (particularly humans). He uses the evidence for the former to argue that sperm competition between sperm does not occur in humans. But the evidence he summarises indicates merely that sperm competition between males is not significant in human males, which is well known.

In fact, there is even evidence that sperm from one individual may co-operate*.

But even his attack on the idea that
“The fertilising sperm is some kind of Olympic champion”
Seems a bit confused, because he later says
“Sperm passage up the female tract is more like an extremely challenging military obstacle course than a standard sprint-style swimming race”.
This ‘military obstacle race’ is then generally ‘won’ by a single sperm – so I’m failing to see a big difference, other than in race metaphors.

Plus this is more of a popular article than a scientific one, despite the presence of some references. For instance, he says:
Popular opinion and even many scientists perpetuate the same sperm scenario for humans, but evidence points in a different direction. In fact, despite various lurid claims to the contrary, there’s no convincing evidence that men are biologically adapted for sperm competition.
But there is no reference for scientists actually making the lurid claims he attacks.

With regard to the crypts, he says:
It has been clearly established that sperm are stored in the crypts from which the mucus flows. But our knowledge of the process involved is regrettably restricted to a single study reported in 1980 by the gynaecologist Vaclav Insler and colleagues of Tel Aviv University in Israel.
In this study, 25 women bravely volunteered to be artificially inseminated on the day before scheduled surgical removal of the womb (hysterectomy). Then, Insler and his team microscopically examined sperm stored in the crypts in serial sections of the cervix. Within two hours after insemination, sperm colonised the entire length of the cervix. Crypt size was very variable, and sperm were stored mainly in the larger ones. Insler and colleagues calculated the number of crypts containing sperm and sperm density per crypt. In some women, up to 200,000 sperm were stored in the cervical crypts.
Insler and colleagues also reported that live sperm had actually been found in cervical mucus up to the ninth day after insemination. Summarising available evidence, they suggested that after insemination the cervix serves as a sperm reservoir from which viable sperm are gradually released to make their way up the oviduct. This dramatic finding has been widely cited yet largely ignored, and there has never been a follow-up study.

This might perhaps be because the speculative statement of Insler et al has never been supported by evidence. For example**:
The concept of a cervical sperm reservoir originates primarily from work in the sheep but, although it may be an attractive hypothesis and has been widely accepted for all species with vaginal insemination, there is really only minimal evidence for any such mechanism in the human female tract. Spermatozoa certainly populate the crypts of the cervical epithelium, but a shift from the lower to the upper levels of the cervix has not been demonstrated (2). Since a continuous migration from the vaginal pool into the lower crypts, which could mask such an upward transfer of spermatozoa, is known not to occur, we are forced to accept that spermatozoa "stored" in any particular crypt remain there until being either transferred directly to the uterus or disposed of (probably by phagocytosis since there is a pronounced leukocytosis from the cervical epithelium after insemination (3)). In a continued absence of any definite evidence that any spermatozoa actually leave a crypt after entering it, there is no sound basis for considering the crypts of the cervical mucosa to be organs of sperm storage in the human.
In general (too much to summarise here) the idea that the egg is a complex structure is a very basic and longstanding one in developmental biology, as is the role of the uterus in cryptic sexual selection. There are rather too*** many tropes of the ‘neglected historical evidence that only I can appreciate’ kind for me to really appreciate the article.

*Qu, Y., Chen, Q., Guo, S., Ma, C., Lu, Y., Shi, J., Liu, S., Zhou, T., Noda, T., Qian, J. and Zhang, L., 2020. Cooperation-based sperm clusters mediate sperm oviduct entry and fertilization.
**Mortimer, D., 1991. Behaviour of spermatozoa in the human oviduct. ARCHIVOS DE BIOLOGIA Y MEDICINA EXPERIMENTALES, 24, pp.339-339.
***too many = two: Jack Cohen reference.

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Bird on a Fire
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Re: sperm race myth

Post by Bird on a Fire » Sun Jan 03, 2021 9:27 pm

Thanks for the article, Stephanie.

I do find it plausible that the way research into human reproduction has been conducted - in terms of the questions asked and the way the results are framed - has probably been coloured by researchers' social attitudes and prejudices. Even in ornithological studies (I don't read much about humans), males are typically described as the more active and competitive partner: for instance, we generally talk about the selection pressures on male peacocks to produce long tails, rather than the selection pressures on female peacocks to choose fit males.

At least in the way human reproduction has been taught to me, the story is generally presented as a bunch of sperms racing up the egg tube to the finish line. The role of female selection of sperm has never been emphasised, but seems a priori likely to be important. At the least I'd say the myth exists in the popular imagination, even if active researchers are mindful of it.

For another bird example, lots of people know that in your common village-pond duck, the Mallard, the male has a very long, corkscrew-shaped penis. My informal survey over the years suggests that this is Britain's commonest pub bird fact. People never emphasise the reason for this, which is that females Mallards have long, corkscrew-shaped vaginas: sex is again presented as something that males do to females, and in this case the evidence that females are just as highly adapted definitely did come later. (Female Mallards also have little sperm-storage tubules in their oviducts, similar to the crypts)

So Allo V Psycho's response is interesting. I think it perhaps suggests that researchers into human reproductive physiology might be investigating the role of female selection more than historically, but that those findings have yet to permeate into the way we understand human cultures (anthropology).

To what extent would research on other species be useful here, AvP? For instance, the Mortimer passage you quote says
an attractive hypothesis and has been widely accepted for all species with vaginal insemination, there is really only minimal evidence for any such mechanism in the human female tract
Now, in the bird world, if there is a widely accepted hypothesis that applies to all species with vaginal insemination, we would generally assume that it probably applied to the one we were specially interested in unless there were evidence to, or a strong reason to suspect, the contrary. If there's strong evidence for storing sperm in cervical crypts across mammals, isn't it most likely that human females will be physiologically similar? (I also wonder whether there has been more research since 1991 when that paper was written, and if not why not? ;) )

Anyway, it's always interesting to think about things you think you understand from a new perspective, so cheers.
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Re: sperm race myth

Post by Little waster » Mon Jan 04, 2021 2:43 pm

Bird on a Fire wrote:
Sun Jan 03, 2021 9:27 pm
My informal survey over the years suggests that this is Britain's commonest pub bird fact.
I think you'll find the list actually is:-

1. Ducks' quacks don't echo.
2. Taxmen are like pelicans.
3. The male Oomiigoolies bird has three inch wide testicles but only two inch long legs. It gets its name from the distinctive cry which it utters on landing on the spikey shingle beaches it lives on.
It's meta, so it is allowed.

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dyqik
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Re: sperm race myth

Post by dyqik » Mon Jan 04, 2021 7:52 pm

Little waster wrote:
Mon Jan 04, 2021 2:43 pm
Bird on a Fire wrote:
Sun Jan 03, 2021 9:27 pm
My informal survey over the years suggests that this is Britain's commonest pub bird fact.
I think you'll find the list actually is:-

1. Ducks' quacks don't echo.
2. Taxmen are like pelicans.
3. The male Oomiigoolies bird has three inch wide testicles but only two inch long legs. It gets its name from the distinctive cry which it utters on landing on the spikey shingle beaches it lives on.
And probably something about either Orville or Rod Hull.

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Re: sperm race myth

Post by Bird on a Fire » Mon Jan 04, 2021 10:55 pm

I used to store my sperm in crypts, until some rotten c.nt split on me.
He has the grace of a swan, the wisdom of an owl, and the eye of an eagle—ladies and gentlemen, this man is for the birds!

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