4 ms·

Is this really the case? Do the fittest sperm become the best people? Feels like a streach

XorNot 1y ago
Not at all: we've been doing IVF for a while now, and completely immobile sperm produce healthy normal babies. It's the peacock's tail effect: what relevance does a brightly colored tail have to a male peacock's actual fitness?
- abyssin 1y ago
  The tail’s appearance is a meaningful proxy for the state of health of its holder.
- Retric 1y ago
  IVF has a higher rate of spontaneous abortion which is a more expensive filter for cellular issues. In people losing out on months of reproductive heath is a meaningful downside. In say frogs having a lower percentage of viable eggs is a significant disadvantage. IVF is also associated with congenital malformations etc. Though it’s hard to separate issues preventing normal conception from issues associated with IVF, it’s likely less viable sperm result in a less healthy fetus.
  - XorNot 1y ago
    Almost completely immobile sperm can and have been used to produce healthy viable babies. Otherwise clinically infertile men have children who are both healthy, capable and also not infertile. Which is solid evidence that "sperm quality" is an extremely poor proxy for useful phenotypes in the resulting human being.
    - Retric 1y ago
      “can and have” sure not everything that makes sperm look feeble in a microscope actually represents an issue. Extremely poor is a qualifier that isn’t backed up by your previous statements or actual scientific studies. Further births are very late in the process, rates of success is a critical metric here. There’s significant research in trying to artificially create similar selection criteria because it increases the odds of a successful pregnancy and live birth. https://pmc.ncbi.nlm.nih.gov/articles/PMC7365522/ https://pmc.ncbi.nlm.nih.gov/articles/PMC7365522/ So if you still disagree, how about presenting some actual evidence.
RangerScience 1y ago
That was the common theory for awhile, but I’ve been seeing a few articles that talk about the egg doing things to “select” amongst the sperm
robocat 1y ago
It is just a filter for certain cellular traits. It doesn't filter for many other important traits. A good flagellum doesn't indicate good kidneys. A sperm's existence indicates the father made faithful copies of cells, however the new sperm DNA could be terrible at making faithful copies (ability not proven until after fertilisation). It also depends on how much of the sperm cell comes from the fathers genes, and how much is generated from the new DNA. I didn't find a clear answer to this but the following indicates that the new sperm cell is at least somewhat generated by the sperm DNA: Because nucleotide recombinations can occur during meiosis I, the genetic code of chromosomes of gametes can differ from that of somatic parent cells (ie., progeny cells might express cell-surface antigens that are recognized by the host [the father] as foreign and thus be eliminated by humoral or cellular immune mechanisms). Occluding junctions that interconnect adjacent Sertoli cells shield secondary spermatocytes, spermatids, and spermatozoa from autoimmune recognition. I wonder if there are any organisms where the sperm envelope is made by the dad, and the DNA letter is contained inside? And I'm completely ignoring the mitochondria (Dad's copy are not passed on so should be mostly irrelevant to sperm selection pressures). I'm pretty ignorant of this whole topic - high school biology only.
- throwawaymaths 1y ago
  100% of sperm dna comes from father. but each chromosome could be "grandfathers" or "grandmothers", and usually those chromosomes have one or two crossover events, so, the chromosome goes FFFFFFFFMM for example. (where F = grandfather and M = grandmother)
  - sshine 1y ago
    Does that mean gendering a baby is more determined by factors on the father's side?
    - croisillon 1y ago
      I never explored this scientifically but I have this hunch that a man with more sisters than brothers will tend to have more daughters than sons
moralestapia 1y ago
It's not, the guy is just making stuff up. A lot of what's behind that "selection" there is still unknown; in principle all sperm are, more or less, the same. There's also so many external effects in play that no single sperm cell may actually have a significant advantage over others; e.g. the behavior of the seminal fluid (ph, viscosity), the physical location of the egg, etc. The cartoonish image of sperm swimming towards the egg is pretty much that ... a cartoon. In reality, they're pretty much drifting and their movement is much more like brownian motion than anything else [1]. Reminds me of this sperm race thing that took the spotlight a month ago, after watching the videos [2] ... come on, man. Only someone who is extremely ignorant and/or is lacking severely on their mental abilities (bordering on idiocy), would believe that thing was true. 1: When the sperm is really close to the egg, however, there seems to be a hormone gradient that guides the sperm, preferentially, towards it. 2: https://x.com/beyoncegarden/status/1916278740214047182 https://x.com/beyoncegarden/status/1916278740214047182
- Retric 1y ago
  There’s a big difference between mostly the same and actually the same. A sperm that doesn’t move is extremely unlikely to fertilize an egg. Thus, 1 is a test for fitness among a tiny percentage of total sperm but still a large number. Length of survival is dependent on factors largely put side of sperms control, but sperm lifespan does test for massive genetic abnormality. So yes 99% never get a chance to compete, but meaningful competition still occurs.
  - deleted 1y ago
    [deleted]
im3w1l 1y ago
I don't think the fittest sperm become the fittest people no. But I do think that seriously fucked up genetic errors will make the sperm cell non-viable. So it's more about creating a floor than getting the creme de la cremepie.

Not at all: we've been doing IVF for a while now, and completely immobile sperm produce healthy normal babies. It's the peacock's tail effect: what relevance does a brightly colored tail have to a male peacock's actual fitness?

abyssin 1y ago
The tail’s appearance is a meaningful proxy for the state of health of its holder.
Retric 1y ago
IVF has a higher rate of spontaneous abortion which is a more expensive filter for cellular issues. In people losing out on months of reproductive heath is a meaningful downside. In say frogs having a lower percentage of viable eggs is a significant disadvantage. IVF is also associated with congenital malformations etc. Though it’s hard to separate issues preventing normal conception from issues associated with IVF, it’s likely less viable sperm result in a less healthy fetus.
- XorNot 1y ago
  Almost completely immobile sperm can and have been used to produce healthy viable babies. Otherwise clinically infertile men have children who are both healthy, capable and also not infertile. Which is solid evidence that "sperm quality" is an extremely poor proxy for useful phenotypes in the resulting human being.
  - Retric 1y ago
    “can and have” sure not everything that makes sperm look feeble in a microscope actually represents an issue. Extremely poor is a qualifier that isn’t backed up by your previous statements or actual scientific studies. Further births are very late in the process, rates of success is a critical metric here. There’s significant research in trying to artificially create similar selection criteria because it increases the odds of a successful pregnancy and live birth. https://pmc.ncbi.nlm.nih.gov/articles/PMC7365522/ https://pmc.ncbi.nlm.nih.gov/articles/PMC7365522/ So if you still disagree, how about presenting some actual evidence.

RangerScience 1y ago

That was the common theory for awhile, but I’ve been seeing a few articles that talk about the egg doing things to “select” amongst the sperm

robocat 1y ago

It is just a filter for certain cellular traits. It doesn't filter for many other important traits. A good flagellum doesn't indicate good kidneys. A sperm's existence indicates the father made faithful copies of cells, however the new sperm DNA could be terrible at making faithful copies (ability not proven until after fertilisation). It also depends on how much of the sperm cell comes from the fathers genes, and how much is generated from the new DNA. I didn't find a clear answer to this but the following indicates that the new sperm cell is at least somewhat generated by the sperm DNA: Because nucleotide recombinations can occur during meiosis I, the genetic code of chromosomes of gametes can differ from that of somatic parent cells (ie., progeny cells might express cell-surface antigens that are recognized by the host [the father] as foreign and thus be eliminated by humoral or cellular immune mechanisms). Occluding junctions that interconnect adjacent Sertoli cells shield secondary spermatocytes, spermatids, and spermatozoa from autoimmune recognition. I wonder if there are any organisms where the sperm envelope is made by the dad, and the DNA letter is contained inside? And I'm completely ignoring the mitochondria (Dad's copy are not passed on so should be mostly irrelevant to sperm selection pressures). I'm pretty ignorant of this whole topic - high school biology only.

throwawaymaths 1y ago
100% of sperm dna comes from father. but each chromosome could be "grandfathers" or "grandmothers", and usually those chromosomes have one or two crossover events, so, the chromosome goes FFFFFFFFMM for example. (where F = grandfather and M = grandmother)
- sshine 1y ago
  Does that mean gendering a baby is more determined by factors on the father's side?
  - croisillon 1y ago
    I never explored this scientifically but I have this hunch that a man with more sisters than brothers will tend to have more daughters than sons

moralestapia 1y ago

It's not, the guy is just making stuff up. A lot of what's behind that "selection" there is still unknown; in principle all sperm are, more or less, the same. There's also so many external effects in play that no single sperm cell may actually have a significant advantage over others; e.g. the behavior of the seminal fluid (ph, viscosity), the physical location of the egg, etc. The cartoonish image of sperm swimming towards the egg is pretty much that ... a cartoon. In reality, they're pretty much drifting and their movement is much more like brownian motion than anything else [1]. Reminds me of this sperm race thing that took the spotlight a month ago, after watching the videos [2] ... come on, man. Only someone who is extremely ignorant and/or is lacking severely on their mental abilities (bordering on idiocy), would believe that thing was true. 1: When the sperm is really close to the egg, however, there seems to be a hormone gradient that guides the sperm, preferentially, towards it. 2: https://x.com/beyoncegarden/status/1916278740214047182 https://x.com/beyoncegarden/status/1916278740214047182

Retric 1y ago
There’s a big difference between mostly the same and actually the same. A sperm that doesn’t move is extremely unlikely to fertilize an egg. Thus, 1 is a test for fitness among a tiny percentage of total sperm but still a large number. Length of survival is dependent on factors largely put side of sperms control, but sperm lifespan does test for massive genetic abnormality. So yes 99% never get a chance to compete, but meaningful competition still occurs.
- deleted 1y ago
  [deleted]

im3w1l 1y ago

I don't think the fittest sperm become the fittest people no. But I do think that seriously fucked up genetic errors will make the sperm cell non-viable. So it's more about creating a floor than getting the creme de la cremepie.