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I'm not an evolutionary biologist, but why wouldn't the selection pressure be related to the speed at which offspring are produced, and not the age of the paren

by nardi 6y ago

I'm not an evolutionary biologist, but why wouldn't the selection pressure be related to the speed at which offspring are produced, and not the age of the parent? And why wouldn't a parent that lives a long time and thus produces more offspring be evolutionarily fit?

hackinthebochs 6y ago
There are a lot of factors involved in having viable offspring. For example, you need enough resources to sufficiently feed and nurture the children you already have. So having more offspring than some ideal amount for the environment can be detrimental. But parents also compete with their offspring for resources. Aging and dying is eventually the best thing a parent can do for their children.
- AnthonyMouse 6y ago
  This doesn't really work at the individual level. Parents compete with their children, but so does everybody else. Having two parents competing with you for resources in addition to the other ten thousand people in your local community is not a meaningful difference. Meanwhile if there was an entire community like this then the people living longer still wouldn't be at a disadvantage, the community would just have a different equilibrium. The surviving communities could e.g. have fewer children on average (you only have to replace people who die in accidents) or would expand their territory over time (expanding population can control more territory).
  - hackinthebochs 6y ago
    That's a fair point about competing with the community. I was thinking of "parents" in aggregate, so the previous generation vs the next, but I didn't word it right. But if everyone lived longer than required, i.e. the minimum ideal for raising viable offspring, then this population stood to be out-competed by another population that aged at a more efficient rate. Individuals in a population aging at an optimal rate is an evolutionary advantage to the population.
    - AnthonyMouse 6y ago
      This might explain why genes for aging exist but doesn't really explain why genes for not aging don't exist. You could have a stable community where e.g. 15% of the population doesn't age and not run into community-level problems because they aren't that large of a percentage of the community, so where are they?
      - hackinthebochs 6y ago
        Hard to say. At least in the case of humans, high generational turnover might have been beneficial in our evolution from aquatic apes or whatever our ancestors were to modern humans. And so longevity genes were selected against. It might be the case that most species' environments are too dynamic for super longevity genes to be beneficial rather than faster population adaptation.
ishjoh 6y ago
The older you get the more difficult it is to conceive children as well as raise them. Given that most people have a partner that is roughly the same age as them, and that there would be a much smaller percentage chance of pairing with someone with the same long life trait, the period of time that they are likely to have children probably stays consistent with societal norms. Therefore living a long life wouldn't increase the number of offspring and wouldn't provide any evnolutionary benefit.
- Udik 6y ago
  > The older you get the more difficult it is to conceive children as well as raise them. Are you trying to provide an evolutionary justification for aging by using aging itself as a reason?
  - deleted 6y ago
    [deleted]

by nardi 6y ago

hackinthebochs 6y ago

There are a lot of factors involved in having viable offspring. For example, you need enough resources to sufficiently feed and nurture the children you already have. So having more offspring than some ideal amount for the environment can be detrimental. But parents also compete with their offspring for resources. Aging and dying is eventually the best thing a parent can do for their children.

AnthonyMouse 6y ago
This doesn't really work at the individual level. Parents compete with their children, but so does everybody else. Having two parents competing with you for resources in addition to the other ten thousand people in your local community is not a meaningful difference. Meanwhile if there was an entire community like this then the people living longer still wouldn't be at a disadvantage, the community would just have a different equilibrium. The surviving communities could e.g. have fewer children on average (you only have to replace people who die in accidents) or would expand their territory over time (expanding population can control more territory).
- hackinthebochs 6y ago
  That's a fair point about competing with the community. I was thinking of "parents" in aggregate, so the previous generation vs the next, but I didn't word it right. But if everyone lived longer than required, i.e. the minimum ideal for raising viable offspring, then this population stood to be out-competed by another population that aged at a more efficient rate. Individuals in a population aging at an optimal rate is an evolutionary advantage to the population.
  - AnthonyMouse 6y ago
    This might explain why genes for aging exist but doesn't really explain why genes for not aging don't exist. You could have a stable community where e.g. 15% of the population doesn't age and not run into community-level problems because they aren't that large of a percentage of the community, so where are they?
    - hackinthebochs 6y ago
      Hard to say. At least in the case of humans, high generational turnover might have been beneficial in our evolution from aquatic apes or whatever our ancestors were to modern humans. And so longevity genes were selected against. It might be the case that most species' environments are too dynamic for super longevity genes to be beneficial rather than faster population adaptation.

ishjoh 6y ago

The older you get the more difficult it is to conceive children as well as raise them. Given that most people have a partner that is roughly the same age as them, and that there would be a much smaller percentage chance of pairing with someone with the same long life trait, the period of time that they are likely to have children probably stays consistent with societal norms. Therefore living a long life wouldn't increase the number of offspring and wouldn't provide any evnolutionary benefit.

Udik 6y ago
> The older you get the more difficult it is to conceive children as well as raise them. Are you trying to provide an evolutionary justification for aging by using aging itself as a reason?
- deleted 6y ago
  [deleted]