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Survival of the fittest. You don’t guarantee there’s nothing majorly wrong with the sperm that gets through, but by rejecting 99.99% as failing to be the faste
by Retric 1y ago
Survival of the fittest. You don’t guarantee there’s nothing majorly wrong with the sperm that gets through, but by rejecting 99.99% as failing to be the fastest or survive the longest in a harsh environment we can drastically cut down on the issues with the next generation before investing significant resources into trying to form an embryo.
- internetter 1y agoIs this really the case? Do the fittest sperm become the best people? Feels like a streach
- XorNot 1y agoNot 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 agoThe tail’s appearance is a meaningful proxy for the state of health of its holder.
- Retric 1y agoIVF 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 agoAlmost 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 agoThat 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 agoIt 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 ago100% 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 agoDoes that mean gendering a baby is more determined by factors on the father's side?
- croisillon 1y agoI 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 agoIt'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 agoThere’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 agoI 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.
- derektank 1y agoNot really, the reason so many sperm are needed is because a woman's reproductive tract requires an aggressive immunological response to foreign bodies (which sperm are). The vagina provides a direct route for pathogens through the cervix and uterus to the fallopian tubes (which can be scarred by inflammation resulting in infertility) and they themselves open up directly into the peritoneal cavity (potentially exposing a woman to septic shock or death if an infection reaches it). To protect against that, the vaginal environment is highly acidic, has layers of mucus that shields the cervix, and a high concentration of immune cells proliferate throughout. Men need to produce so many sperm because they need to be able to temporarily overwhelm these defenses.
- adrian_b 1y agoWhat you say is right, but it does not contradict the parent poster. Both reasons for the high count of sperm cells are true. There must be many sperm cells to survive the adverse conditions, but there is also intense competition with the sibling sperm cells. The DNA of the sperm cells is generated by a random generator, which is the meiosis mechanism, which randomly shuffles then randomly discards half of the father DNA. The sperm competition then discards the random choices that happened to be bad, implementing an optimum search algorithm. The sperm competition is only a first filter for rejecting bad random choices. Many embryos will die very soon, without ever developing, rejecting other bad random choices.
- metalman 1y agoas to the large number of sperm required, it is note worthy that excess male germ cell's is the norm for many?, most?, all?, species, and that in a lot of cases there is a number of complications involved in transfering them to a female, and altogether improbable solutions, also the basic mechanisms for germ cells are conserved by plants and animals, "pollen" bieng tailess sperm.....except in the case of ginko trees, that have motile sperm so the real questions are around why did evolution produce, and stick to this mechanism, and not so much about our species rather mundane take on it.
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- eviks 1y agoThis doesn't help much: - You can reject 99.99% in thousands, not millions - How is swimming fastest relevant to the genetic information quality inside?
- Retric 1y agoIt’s not the sperms fault it ends the night on a body instead of someplace useful. Random luck is therefore a filer dropping from millions to thousands without telling you anything about the sperm. It’s useless for all that multicellular goodness that separates humans from fish. But making viable single cells is a prerequisite for everything that comes after. DNA that can’t make cell walls etc can’t make a person as such there’s a host of genetic anomalies that don’t result in a fetus let alone a live birth.
- eviks 1y agoWait, but random luck is precisely the thing that breaks this whole "fittest" model since there isn't a selection for fitness! (that was my other major issue I didn't mention with this whole approach) Add luck doesn't explain millions either, it would sound the same if thousands dropped to hundreds
- Retric 1y agoRandom bad luck is always part of any survival of the fittest situation. A meteor killing few thousand trees isn’t something a given tree at the center of the impact crater can do much about. Also, it’s “fittest” as category not most fit as a ranking. Perhaps a better conceptual model is people who finish a marathon are a fitter group than those who start a marathon even if someone who failed was potentially in better shape than the winner. Many species have thousands of offspring because the odds any one of them reproduces is very low, a valid strategy not some sign of incompetence. > Add luck doesn't explain millions either, it would sound the same if thousands dropped to hundreds The actual cause is the full evolutionary history going back to the first life form and the environment each generation lived in, but we can still examine individual elements of what’s going on. “Luck” is a multiplier on the number of sperm needed. The ability of an individual sperm to optimize its odds of success is a sign of cellular function. There’s zero contradiction between those statements. ~1:10,000 * ~1:100