7 ms·

Sperm are very different from all other cells

79 points by viewtransform 1y ago

pbw 1y ago
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.
- Metacelsus 1y ago
  And it's not like you need 50 million to fertilize the egg. It just gives a better chance of out-competing the other guy's sperm!
- yesco 1y ago
  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).
  - Analemma_ 1y ago
    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.
    - elcritch 1y ago
      > And in any event, evolution always selects for the fitness of the individual, not the species— group selection is a very controversial topic in evobio, but the general consensus is that it does not happen To me that seems more to me like a group of academics who just can’t see “how” it’d work. We’ve seen that in field after field where practitioners rarely look outside their own field. There’s no “magic” in evolution to make it work only on individuals. Evolution is going to follow game theory. In some scenarios the evolution of the group will over time be far more adaptive than that of an individual. It’s a math question, not a biology question.
    - yesco 1y ago
      I suspect there could be a misalignment in semantics here, and not necessarily a disagreement. When a biologist says "evolutionary pressure" perhaps they have a different way of modeling what that means to them? To me evolutionary pressure isn't an on/off thing, it's like a signal in the noise. It's a vector with a direction and magnitude, facing varying levels of environmental resistance. To be more specific, if there was enough "magnitude", evolution could potentially arrive at a perfect CRC. But the "resistance" requires a "magnitude" higher than evolution is willing to pay to reach that perfection. Likely in part due to the implicit complexity slope. Considering the systemic malfunction mutation can cause, one might assume this magnitude would be higher than it currently is. However, this is entirely speculation, and not falsifiable. So when I think of evolutionary pressure I'm considering it as a component of the final vector, where a biologist might more pragmatically consider the total sum of vectors instead. This way of thinking is likely more productive for what they are doing. As for evolution always selecting for the individual over the group, I'm surprised this is controversial when it's so obviously happening? If that was true how could multicellular organisms even exist? I'm very much not an expert on any of this, but this sounds like perhaps an over focus on DNA itself and not evolution as a whole, but maybe I'm misunderstanding something?
      - smogcutter 1y ago
        > This way of thinking is likely more productive for what they are doing. Which is… attempting a rigorous understanding of evolutionary biology, rather than idly ruminating. I hate to use a dork-ism like “update your priors”, but this is actually maybe a situation where it applies? If you’re serious about a subject it’s more interesting to really incorporate the likelihood that you’re wrong than it is to wave it away as semantics or point of view.
  - gus_massa 1y ago
    But there are also Microsatellites https://en.wikipedia.org/wiki/Microsatellite#Mutation_mechanisms_and_mutation_rates 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.
- 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 ago
    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.
- jacobedawson 1y ago
  Come on lads! Don't give up, we're only just past the tonsils!
  - deleted 1y ago
    [deleted]
  - snickerbockers 1y ago
    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.
    - cwmoore 1y ago
      Experimental science has yet to determine whether this is not due to morphic resonance or love.
    - anon25783 1y ago
      ...Huh. So does this increased biodiversity mean that I have, perhaps, stronger immune defenses or quicker healing in certain oral tissues due to hybrid vigor[1] in the back of my throat? [1] https://en.wikipedia.org/wiki/Heterosis https://en.wikipedia.org/wiki/Heterosis
- XorNot 1y ago
  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.
  - derektank 1y ago
    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.
- seydor 1y ago
  They are like investors looking for startups
- gabesullice 1y ago
  https://lumiere-a.akamaihd.net/v1/images/image_7b0b0044.jpeg https://lumiere-a.akamaihd.net/v1/images/image_7b0b0044.jpeg
- globular-toast 1y ago
  Then: how many of these "male" individuals should we produce? 10%? Could probably get away with 5%... Nah, let's do 50%.
  - HK-NC 1y ago
    Let the games begin.
- gus_massa 1y ago
  Female chimps mate with many male chimps, so they have big testis and lot of sperm. If one sends 100 and the next 1000000 guess who is going to win.
AStonesThrow 1y ago
[dead]
havaloc 1y ago
Seems very Star Trek Enterprise when they polarize the hull plating. "To prevent this from happening, once a sperm cell has made contact with it, the egg quickly employs two mechanisms. First, its plasma membrane rapidly depolarises – meaning it creates an electrical barrier that further sperm cannot cross."
tsoukase 1y ago
Whatever relates to DNA in an organism is under strict control and huge protective mechanisms. For example DNA replication has an error rate of 1/10^9. Obviously, selecting 1 out of 10-150 million "persons" is some fierce form of survival of the fittest, that happens early and is very cheap. The next layer of selection is embryonic development, next the labor and in the end early life diseases. At every level the selection becomes weaker but the price larger. We are some pretty special and die-hard persons.
snickerbockers 1y ago
[flagged]

79 points by viewtransform 1y ago

pbw 1y ago

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.

Metacelsus 1y ago
And it's not like you need 50 million to fertilize the egg. It just gives a better chance of out-competing the other guy's sperm!
yesco 1y ago
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).
- Analemma_ 1y ago
  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.
  - elcritch 1y ago
    > And in any event, evolution always selects for the fitness of the individual, not the species— group selection is a very controversial topic in evobio, but the general consensus is that it does not happen To me that seems more to me like a group of academics who just can’t see “how” it’d work. We’ve seen that in field after field where practitioners rarely look outside their own field. There’s no “magic” in evolution to make it work only on individuals. Evolution is going to follow game theory. In some scenarios the evolution of the group will over time be far more adaptive than that of an individual. It’s a math question, not a biology question.
  - yesco 1y ago
    I suspect there could be a misalignment in semantics here, and not necessarily a disagreement. When a biologist says "evolutionary pressure" perhaps they have a different way of modeling what that means to them? To me evolutionary pressure isn't an on/off thing, it's like a signal in the noise. It's a vector with a direction and magnitude, facing varying levels of environmental resistance. To be more specific, if there was enough "magnitude", evolution could potentially arrive at a perfect CRC. But the "resistance" requires a "magnitude" higher than evolution is willing to pay to reach that perfection. Likely in part due to the implicit complexity slope. Considering the systemic malfunction mutation can cause, one might assume this magnitude would be higher than it currently is. However, this is entirely speculation, and not falsifiable. So when I think of evolutionary pressure I'm considering it as a component of the final vector, where a biologist might more pragmatically consider the total sum of vectors instead. This way of thinking is likely more productive for what they are doing. As for evolution always selecting for the individual over the group, I'm surprised this is controversial when it's so obviously happening? If that was true how could multicellular organisms even exist? I'm very much not an expert on any of this, but this sounds like perhaps an over focus on DNA itself and not evolution as a whole, but maybe I'm misunderstanding something?
    - smogcutter 1y ago
      > This way of thinking is likely more productive for what they are doing. Which is… attempting a rigorous understanding of evolutionary biology, rather than idly ruminating. I hate to use a dork-ism like “update your priors”, but this is actually maybe a situation where it applies? If you’re serious about a subject it’s more interesting to really incorporate the likelihood that you’re wrong than it is to wave it away as semantics or point of view.
- gus_massa 1y ago
  But there are also Microsatellites https://en.wikipedia.org/wiki/Microsatellite#Mutation_mechanisms_and_mutation_rates 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.
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 ago
  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.
jacobedawson 1y ago
Come on lads! Don't give up, we're only just past the tonsils!
- deleted 1y ago
  [deleted]
- snickerbockers 1y ago
  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.
  - cwmoore 1y ago
    Experimental science has yet to determine whether this is not due to morphic resonance or love.
  - anon25783 1y ago
    ...Huh. So does this increased biodiversity mean that I have, perhaps, stronger immune defenses or quicker healing in certain oral tissues due to hybrid vigor[1] in the back of my throat? [1] https://en.wikipedia.org/wiki/Heterosis https://en.wikipedia.org/wiki/Heterosis
XorNot 1y ago
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.
- derektank 1y ago
  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.
seydor 1y ago
They are like investors looking for startups
gabesullice 1y ago
https://lumiere-a.akamaihd.net/v1/images/image_7b0b0044.jpeg https://lumiere-a.akamaihd.net/v1/images/image_7b0b0044.jpeg
globular-toast 1y ago
Then: how many of these "male" individuals should we produce? 10%? Could probably get away with 5%... Nah, let's do 50%.
- HK-NC 1y ago
  Let the games begin.
gus_massa 1y ago
Female chimps mate with many male chimps, so they have big testis and lot of sperm. If one sends 100 and the next 1000000 guess who is going to win.

AStonesThrow 1y ago

[dead]

havaloc 1y ago

Seems very Star Trek Enterprise when they polarize the hull plating. "To prevent this from happening, once a sperm cell has made contact with it, the egg quickly employs two mechanisms. First, its plasma membrane rapidly depolarises – meaning it creates an electrical barrier that further sperm cannot cross."

tsoukase 1y ago

Whatever relates to DNA in an organism is under strict control and huge protective mechanisms. For example DNA replication has an error rate of 1/10^9. Obviously, selecting 1 out of 10-150 million "persons" is some fierce form of survival of the fittest, that happens early and is very cheap. The next layer of selection is embryonic development, next the labor and in the end early life diseases. At every level the selection becomes weaker but the price larger. We are some pretty special and die-hard persons.

snickerbockers 1y ago

[flagged]