4 ms·

Theoretical work by Fisher, Medawar, and Hamilton during the last century pretty much explained why we see super-exponential decay in mortality distributions. T

by jostmey 12y ago

Theoretical work by Fisher, Medawar, and Hamilton during the last century pretty much explained why we see super-exponential decay in mortality distributions. Their theories center around using the "Euler-Lotka Equation", which estimates the number of descendants from an individual considering that each member ages. You can then show that the effect of aging on fitness is marginal, and hence not selected against. This might be one of the more accessible papers: http://www.genetics.org/content/156/3/927.short#ref-10 http://www.genetics.org/content/156/3/927.short#ref-10

jostmey 12y ago
P.S. And yes, Mother Nature did not build us to last. Natural selection seems to have little regard for longevity.
- tachyonbeam 12y ago
  There are plants that seem to last indefinitely and never really die, this one, for example: http://en.wikipedia.org/wiki/Chlorophytum http://en.wikipedia.org/wiki/Chlorophytum I think the real issue is that when it comes to complex animals, it's much easier to build a brand new one than to repair existing ones. Our genes encode how to grow a human from scratch, but now how to deal with the myriad of problems that can occur as a result of normal wear and tear. Repairing an ageing body is a completely different problem from growing one. We do have some DNA that deals with maintenance processes, but I think the issue is that these processes inevitably can't cope. It's like trying to patch up an old house. You can keep doing little fixes here and there, but at some point, serious renovations are needed, and we're just not genetically equipped to do that. You have to wonder what it is nature could do anyway, if humans living to be extremely old had been selected for. Old human bodies are so broken, we'd need to be able to grow entirely new ones and shed body parts, even regrow brain tissue. We'd need a metamorphosis on the level of what butterflies go through.
  - emn13 12y ago
    [citation needed] - wikipedia makes no mention of this extremely unusual property. Apparently some people think even bacteria age - http://www.sciencedaily.com/releases/2011/10/111027150207.htm http://www.sciencedaily.com/releases/2011/10/111027150207.ht... (whatever that means in an organism that divides).
  - rogerbinns 12y ago
    Matt Ridley's The Red Queen also talks about the effects of parasites, which also maps in to why there are genders (more accurately sexual reproduction). The problem is the mismatch between lengths of generations. A parasite that has one generation every week gets 52 shots a year at an unchanging host. As time passes the probability of success for the parasite increases. The human with ~20 years per generation has to withstand that long before making a new one that is different and (partially) resets the clock. Gender comes in because asexual reproduction would produce offspring virtually identical to their parent which means a successful parasite would have a large number of hosts to exploit. By combining DNA from two different individuals (note how much we avoid individuals from the same family with substantially similar DNA) things are mixed up enough to give a head start against the parasites. https://en.wikipedia.org/wiki/The_Red_Queen:_Sex_and_the_Evolution_of_Human_Nature https://en.wikipedia.org/wiki/The_Red_Queen:_Sex_and_the_Evo...
- eevilspock 12y ago
  > Natural selection seems to have little regard for longevity. I'd argue the opposite, that natural selection depends entirely on death, not just to weed out the less fit, but also because Without death, there would be no evolution. This is by definition, at least for an environment that can only support a limited population. Corollary: The maximum rate of evolution is proportional to the rate of generation turnover, that is to say it is inversely proportional to life span. (http://qr.ae/L5v6z http://qr.ae/L5v6z) Mother Nature did not build us to last, but quite "intentionally".
  - trhway 12y ago
    > The maximum rate of evolution is proportional to the rate of generation turnover, that is to say it is inversely proportional to life span. it is true for r-selection only.
    - eevilspock 12y ago
      First, r/K selection is a theory, a controversial one at that (https://en.wikipedia.org/wiki/R/K_selection_theory#Status https://en.wikipedia.org/wiki/R/K_selection_theory#Status). Second, there is no contradiction between the two theories. According to r/K selection, long life-span is a typical characteristic of K-selected species, while short lifespan is typical for the r-selected. The theory I espouse would simple add that the continuum between K-selected and r-selected species would tend to correspond to a continuum of evolutionary rates. If you still disagree, please follow the link and point out flaws in the argument.
      - trhway 12y ago
        >The theory I espouse would simple add that the continuum between K-selected and r-selected species would tend to correspond to a continuum of evolutionary rates. Looking at the last 2B years who has shown higher "global" evolutionary rate - the line of living matter leading to humans or the line leading to fish? While of course it is obvious that the "local" evolutionary rate - rate of producing and churning through minor changes - is higher for shorter lived. In short - giving the result the human rate of evolution
jessriedel 12y ago
Do they successfully predict any data besides the super-exponential decay?
- jostmey 12y ago
  I think I can do better. Michael Rose breed fruit flies selecting for longevity. I believed his work showed that it was possible to extend lifespan simply by introducing the right selective pressure. If this doesn't demonstrate that aging is the result of Evolutionary processes, I don't know what will. Here's his profile: https://scholar.google.com/citations?user=NCQ3E5sAAAAJ&hl=en&oi=ao https://scholar.google.com/citations?user=NCQ3E5sAAAAJ&hl=en...
  - jessriedel 12y ago
    No one reasonably disputes that aging is the result of an evolutionary process. But that's a far cry from explaining exactly "why we see super-exponential decay in mortality distributions".
DavidSJ 12y ago
That seems to explain why evolution hasn't done much to stop aging, but it doesn't describe the mechanisms of aging itself, which cause mortality rates to increase over time with this particular curve.

by jostmey 12y ago

jostmey 12y ago

P.S. And yes, Mother Nature did not build us to last. Natural selection seems to have little regard for longevity.

tachyonbeam 12y ago
There are plants that seem to last indefinitely and never really die, this one, for example: http://en.wikipedia.org/wiki/Chlorophytum http://en.wikipedia.org/wiki/Chlorophytum I think the real issue is that when it comes to complex animals, it's much easier to build a brand new one than to repair existing ones. Our genes encode how to grow a human from scratch, but now how to deal with the myriad of problems that can occur as a result of normal wear and tear. Repairing an ageing body is a completely different problem from growing one. We do have some DNA that deals with maintenance processes, but I think the issue is that these processes inevitably can't cope. It's like trying to patch up an old house. You can keep doing little fixes here and there, but at some point, serious renovations are needed, and we're just not genetically equipped to do that. You have to wonder what it is nature could do anyway, if humans living to be extremely old had been selected for. Old human bodies are so broken, we'd need to be able to grow entirely new ones and shed body parts, even regrow brain tissue. We'd need a metamorphosis on the level of what butterflies go through.
- emn13 12y ago
  [citation needed] - wikipedia makes no mention of this extremely unusual property. Apparently some people think even bacteria age - http://www.sciencedaily.com/releases/2011/10/111027150207.htm http://www.sciencedaily.com/releases/2011/10/111027150207.ht... (whatever that means in an organism that divides).
- rogerbinns 12y ago
  Matt Ridley's The Red Queen also talks about the effects of parasites, which also maps in to why there are genders (more accurately sexual reproduction). The problem is the mismatch between lengths of generations. A parasite that has one generation every week gets 52 shots a year at an unchanging host. As time passes the probability of success for the parasite increases. The human with ~20 years per generation has to withstand that long before making a new one that is different and (partially) resets the clock. Gender comes in because asexual reproduction would produce offspring virtually identical to their parent which means a successful parasite would have a large number of hosts to exploit. By combining DNA from two different individuals (note how much we avoid individuals from the same family with substantially similar DNA) things are mixed up enough to give a head start against the parasites. https://en.wikipedia.org/wiki/The_Red_Queen:_Sex_and_the_Evolution_of_Human_Nature https://en.wikipedia.org/wiki/The_Red_Queen:_Sex_and_the_Evo...
eevilspock 12y ago
> Natural selection seems to have little regard for longevity. I'd argue the opposite, that natural selection depends entirely on death, not just to weed out the less fit, but also because Without death, there would be no evolution. This is by definition, at least for an environment that can only support a limited population. Corollary: The maximum rate of evolution is proportional to the rate of generation turnover, that is to say it is inversely proportional to life span. (http://qr.ae/L5v6z http://qr.ae/L5v6z) Mother Nature did not build us to last, but quite "intentionally".
- trhway 12y ago
  > The maximum rate of evolution is proportional to the rate of generation turnover, that is to say it is inversely proportional to life span. it is true for r-selection only.
  - eevilspock 12y ago
    First, r/K selection is a theory, a controversial one at that (https://en.wikipedia.org/wiki/R/K_selection_theory#Status https://en.wikipedia.org/wiki/R/K_selection_theory#Status). Second, there is no contradiction between the two theories. According to r/K selection, long life-span is a typical characteristic of K-selected species, while short lifespan is typical for the r-selected. The theory I espouse would simple add that the continuum between K-selected and r-selected species would tend to correspond to a continuum of evolutionary rates. If you still disagree, please follow the link and point out flaws in the argument.
    - trhway 12y ago
      >The theory I espouse would simple add that the continuum between K-selected and r-selected species would tend to correspond to a continuum of evolutionary rates. Looking at the last 2B years who has shown higher "global" evolutionary rate - the line of living matter leading to humans or the line leading to fish? While of course it is obvious that the "local" evolutionary rate - rate of producing and churning through minor changes - is higher for shorter lived. In short - giving the result the human rate of evolution

jessriedel 12y ago

Do they successfully predict any data besides the super-exponential decay?

jostmey 12y ago
I think I can do better. Michael Rose breed fruit flies selecting for longevity. I believed his work showed that it was possible to extend lifespan simply by introducing the right selective pressure. If this doesn't demonstrate that aging is the result of Evolutionary processes, I don't know what will. Here's his profile: https://scholar.google.com/citations?user=NCQ3E5sAAAAJ&hl=en&oi=ao https://scholar.google.com/citations?user=NCQ3E5sAAAAJ&hl=en...
- jessriedel 12y ago
  No one reasonably disputes that aging is the result of an evolutionary process. But that's a far cry from explaining exactly "why we see super-exponential decay in mortality distributions".

DavidSJ 12y ago

That seems to explain why evolution hasn't done much to stop aging, but it doesn't describe the mechanisms of aging itself, which cause mortality rates to increase over time with this particular curve.