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.
The best sperm will likely result in the next generation of sperm also being good.
We look at the human as the organism, the sperm as the gamete - but perhaps our logic is anthropocentric - perhaps the sperm is the organism, and we are just the ridiculously elaborate reproductive mechanism.
I remember something like they may have sexual reproduction and even form blastulas, but the Wiki article is not very clear, so I may be misremembering.
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)
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.
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.
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.
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.
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:
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.
I suppose it’s a question of perspective.
The best sperm will likely result in the next generation of sperm also being good.
We look at the human as the organism, the sperm as the gamete - but perhaps our logic is anthropocentric - perhaps the sperm is the organism, and we are just the ridiculously elaborate reproductive mechanism.
The current best guess is that animals evolved from https://en.wikipedia.org/wiki/Choanoflagellate They look quite similar to sperm.
I remember something like they may have sexual reproduction and even form blastulas, but the Wiki article is not very clear, so I may be misremembering.
> we are just the ridiculously elaborate reproductive mechanism
That is the point behind Dawkins' The Selfish Gene.
The book well argues that genes are what reproduce, and that everything else is just complications to reproduce genes.
Humbling book - not light reading but I love it and I read it again and again because of the unobvious insights into systems.
We are (for genes, though, not sperm)
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)
I assumed F = Frances and M = Michael, my paternal grandparent's names, so thanks for the clarification.
Does that mean gendering a baby is more determined by factors on the father's side?
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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.
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
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
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.
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?
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.
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.
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The tail’s appearance is a meaningful proxy for the state of health of its holder.