We need to get the male’s genetic material into the female’s body. How many redundant copies should we send. 100? 1000? A voice in back of the room: 50 million.
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.
Not 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.
I'm broadly speculating here, but I tend to view most mechanisms like this as evolution's "desire" for a well tuned, but imperfect, CRC check.
Ignoring whether or not it would even be possible, a perfect CRC is antithetical to evolution itself, wiggle room for mutation must always be possible, but too much mutation gives you cancer and systemic malfunction. So you end up with these bizarre processes that allow just the right amount of imperfection.
With sperm specifically it ends up closer to a signature check than just a CRC, if the sperm doesn't exhibit behavior that falls under a certain umbrella of expected behaviors, it's rejected by the surrounding environment. The difficulty to comprehend it could even be a feature of the process in many respects, especially when you consider everything in this realm risks getting "hacked" if precautions are not put into place.
So when I see huge numbers like this, I see it as an indirect measure of the precision of the overall process. To put it another way, it's like brute forcing a password you don't know, but happen to have a lot of hints to (since obviously, we are all still the same species at the end of the day).
I’ve actually had this question myself, “is there evolutionary pressure for imperfect genetic copying and repair mechanisms, since perfect ones would halt evolution and leave a species unable to adapt?”
I’ve asked this question to multiple evolutionary biologists, and all of them answered “no” very strongly, strongly enough that I’m inclined to believe it. Apparently the frequency of deleterious mutations is many orders of magnitude greater than the frequency of beneficial ones, meaning there’s little chance perfect copying could be maladaptive. And in any event, evolution always selects for the fitness of the individual, not the species— group selection is a controversial topic in evobio, but the general consensus is that it does not happen, and that the rare things which kinda look like group selection (e.g. eusociality in bees) actually aren’t and can be explained without it.
But there are also Microsatellites https://en.wikipedia.org/wiki/Microsatellite#Mutation_mechan... that are repeated sequences in the DNA. It's difficult to copy the correct number of repetitions, so they have a higher mutation rate. It's like like a controlled localized increased rate of mutation.
A better way to think about it is just how much surface area of uterus the ovum could actually be in.
It's not that you need millions of sperm or that millions of sperm are competing, its that those sorts of numbers are necessary just to make it probably at least 1 sperm even finds the egg while it's still got energy.
Sperm are actually quite good at finding the egg if they make it to the fallopian tube, they have their own chemoreceptors that can detect very small changes in chemical gradients, but only a few hundred make it through the preceding gauntlet.
There's this fascinating phenomenon called "micro chimerism"where somehow they've found that some of the cells in women's bodies are actually descendents of cells from past sexual partners, and they can be found in places far removed from the reproductive tract. the relation to your comment is that the tonsils and throat are known to be susceptible to this.
Fun rabbit hole, in since cases they think it's the result of cells from offspring winding up in the wrong side of the umbilical but there are also cases where there was never a pregnancy in which case it has to be wayward sperm but that's absolutely bizarre and far too orthogonal to the sperms primary objective.
And AFAIK they don't have any idea of why this is beneficial to the woman or even to the man who created the invasive cells.
Retric|8 months ago
internetter|8 months ago
derektank|8 months ago
eviks|8 months ago
- You can reject 99.99% in thousands, not millions
- How is swimming fastest relevant to the genetic information quality inside?
yesco|8 months ago
Ignoring whether or not it would even be possible, a perfect CRC is antithetical to evolution itself, wiggle room for mutation must always be possible, but too much mutation gives you cancer and systemic malfunction. So you end up with these bizarre processes that allow just the right amount of imperfection.
With sperm specifically it ends up closer to a signature check than just a CRC, if the sperm doesn't exhibit behavior that falls under a certain umbrella of expected behaviors, it's rejected by the surrounding environment. The difficulty to comprehend it could even be a feature of the process in many respects, especially when you consider everything in this realm risks getting "hacked" if precautions are not put into place.
So when I see huge numbers like this, I see it as an indirect measure of the precision of the overall process. To put it another way, it's like brute forcing a password you don't know, but happen to have a lot of hints to (since obviously, we are all still the same species at the end of the day).
Analemma_|8 months ago
I’ve asked this question to multiple evolutionary biologists, and all of them answered “no” very strongly, strongly enough that I’m inclined to believe it. Apparently the frequency of deleterious mutations is many orders of magnitude greater than the frequency of beneficial ones, meaning there’s little chance perfect copying could be maladaptive. And in any event, evolution always selects for the fitness of the individual, not the species— group selection is a controversial topic in evobio, but the general consensus is that it does not happen, and that the rare things which kinda look like group selection (e.g. eusociality in bees) actually aren’t and can be explained without it.
gus_massa|8 months ago
Metacelsus|8 months ago
gabesullice|8 months ago
XorNot|8 months ago
It's not that you need millions of sperm or that millions of sperm are competing, its that those sorts of numbers are necessary just to make it probably at least 1 sperm even finds the egg while it's still got energy.
derektank|8 months ago
gus_massa|8 months ago
globular-toast|8 months ago
HK-NC|8 months ago
seydor|8 months ago
jacobedawson|8 months ago
snickerbockers|8 months ago
Fun rabbit hole, in since cases they think it's the result of cells from offspring winding up in the wrong side of the umbilical but there are also cases where there was never a pregnancy in which case it has to be wayward sperm but that's absolutely bizarre and far too orthogonal to the sperms primary objective.
And AFAIK they don't have any idea of why this is beneficial to the woman or even to the man who created the invasive cells.
unknown|8 months ago
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