3 ms·

Years ago, I published a paper suggesting that humans have genomic evidence of strong selection pressure on some sex hormone pathways. So, I am quite curious ab

Years ago, I published a paper suggesting that humans have genomic evidence of strong selection pressure on some sex hormone pathways. So, I am quite curious about whether sperm counts are plummeting solely because of environmental changes (e.g., human created hormone influencing toxins, including "the pill") or also because natural selection in humans has drastically changed with the advent of modern society. In species with highly promiscuous females, sperm counts tend to go up as a response to competition among males (and their cellular representatives). However, in societies that have birth control as the norm, pregnancy is primarily a result of conscious choice (stable relationship, financial status, etc). Consequently, sperm count is under drastically less selection pressure because you have multiple shots on goal without much reproductive consequences, so to speak.

seydor 4y ago
Wasn't Sexual selection even more weird throughout recorded history? Marriage concerns basically was the opposite of SS , where economics and religion trumped natural selection, particularly in the western world we re talking about. Even today millions of people are marrying contrary to selection gradients (arranged marriages, marrying relatives, too young/old , excluding other religions etc etc.). Do these people have lower/higher sperm counts?
- akiselev 4y ago
  For the vast majority of recorded history people married someone from their village of 200 people or from a nearby village a few miles away. It doesn't matter how weird our mating rituals are when there's not much variability to begin with. Modern urban cities provide access to a much more diverse gene pool which allows individuals to select across a much wider range of characteristics.
  - seydor 4y ago
    Then it seems that sexual selection selects for weaker sperm? That sounds like a contradiction
    - biomcgary 4y ago
      Sexual selection is invoked to explain all sorts of things that seem counter-intuitive at face value. The best know example is peacock feathers, which make males more susceptible to predators and are energetically costly. Thus, a male who has an elaborate display must be healthier and more vigorous than one that does not.
nosianu 4y ago
So how do you integrate into your theory the additional fact mentioned in that article that sperm count and male health were associated? > “One can view the decline in sperm counts as a biomarker for male health in general,” says Kristensen. > In fact, a study in a 2018 issue of the journal Andrology found a higher risk of hospitalization among men who had lower sperm concentrations. Those with sperm concentrations below 15 million/mL—considered low—had a 53 percent greater risk of being hospitalized for any reason over the course of 36 years than those with more robust sperm concentrations between 51 and 100 million/mL. This effect persisted even after the researchers controlled for body weight, smoking, and other factors. Sounds to me like that supports the chemicals theory.
- biomcgary 4y ago
  Possibly chemicals, but, alternatively, natural selection has been relaxed across the board in the modern societies since agriculture and even more after industrialization. How often do you see males literally fighting over sexual access to a female, which would select for physically healthy males? Selection pressure for intelligence may have increased, but education level is negatively correlated with reproduction, so maybe not. Multiple generations of relaxed selection would have a cumulative effect on health AND sperm production.
  - nosianu 4y ago
    > natural selection has been relaxed across the board in the modern societies since agriculture and even more after industrialization Citation very much needed. Women nowadays accept males indiscriminately? Reproduction success is the same for everybody across the board? That's news to me and I very much doubt the veracity of such a bold claim. Natural selection is very much alive.

seydor 4y ago

Wasn't Sexual selection even more weird throughout recorded history? Marriage concerns basically was the opposite of SS , where economics and religion trumped natural selection, particularly in the western world we re talking about. Even today millions of people are marrying contrary to selection gradients (arranged marriages, marrying relatives, too young/old , excluding other religions etc etc.). Do these people have lower/higher sperm counts?

akiselev 4y ago
For the vast majority of recorded history people married someone from their village of 200 people or from a nearby village a few miles away. It doesn't matter how weird our mating rituals are when there's not much variability to begin with. Modern urban cities provide access to a much more diverse gene pool which allows individuals to select across a much wider range of characteristics.
- seydor 4y ago
  Then it seems that sexual selection selects for weaker sperm? That sounds like a contradiction
  - biomcgary 4y ago
    Sexual selection is invoked to explain all sorts of things that seem counter-intuitive at face value. The best know example is peacock feathers, which make males more susceptible to predators and are energetically costly. Thus, a male who has an elaborate display must be healthier and more vigorous than one that does not.

nosianu 4y ago

So how do you integrate into your theory the additional fact mentioned in that article that sperm count and male health were associated? > “One can view the decline in sperm counts as a biomarker for male health in general,” says Kristensen. > In fact, a study in a 2018 issue of the journal Andrology found a higher risk of hospitalization among men who had lower sperm concentrations. Those with sperm concentrations below 15 million/mL—considered low—had a 53 percent greater risk of being hospitalized for any reason over the course of 36 years than those with more robust sperm concentrations between 51 and 100 million/mL. This effect persisted even after the researchers controlled for body weight, smoking, and other factors. Sounds to me like that supports the chemicals theory.

biomcgary 4y ago
Possibly chemicals, but, alternatively, natural selection has been relaxed across the board in the modern societies since agriculture and even more after industrialization. How often do you see males literally fighting over sexual access to a female, which would select for physically healthy males? Selection pressure for intelligence may have increased, but education level is negatively correlated with reproduction, so maybe not. Multiple generations of relaxed selection would have a cumulative effect on health AND sperm production.
- nosianu 4y ago
  > natural selection has been relaxed across the board in the modern societies since agriculture and even more after industrialization Citation very much needed. Women nowadays accept males indiscriminately? Reproduction success is the same for everybody across the board? That's news to me and I very much doubt the veracity of such a bold claim. Natural selection is very much alive.