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Evolutionary theory would also suggest that we have some mechanism to ensure our deaths. Longer lifespans cause fewer generations per time period, resulting in

Evolutionary theory would also suggest that we have some mechanism to ensure our deaths. Longer lifespans cause fewer generations per time period, resulting in less adaptability as a species.

VMG 15y ago
Longer lifespans cause fewer generations per time period Only if you assume the non-reproductive members are a net negative (grandparents becoming a burden)
- deleted 15y ago
  [deleted]
- fragsworth 15y ago
  Actually no, it's a little more complex than that: Regardless of reproductive lifespan, in a population that is in equilibrium (not increasing or decreasing significantly), the average number of (surviving and reproducing) children per individual is going to be 2. So supposing we could live to be 1000 years old, and still reproduce at that age, we'd have an average of 2 generations per 1000 years.
  - mrbgty 15y ago
    I'm curious. What backs up the idea that the average number of children per individual will be 2 regardless of reproductive lifespan? It seems that I've seen a somewhat(?) common pattern among people who have young families and get divorced that often times have another family (+2 children) when they re-marry.
    - jowiar 15y ago
      The definition of equilibrium. Every child has 2 parents. Thus in each reproduction, every parent creates on average half a child (sounds rather morbid). Thus for the population to remain in equilibrium, each person needs to reproduce, on average, twice.
  - Wilduck 15y ago
    But lifespan and reproductive lifespan are different. Suppose we could live to be 1000, but only reproduce from ages 15 to 65. Then the equilibrium number of years per generation would be right around 40.
  - VMG 15y ago
    Why should genes strive for an equilibrium? Even humans for most of history tried to have as many offspring as possible.
    - fragsworth 15y ago
      It has nothing to do with genes - every population eventually hits a maximum capacity, after which it normally remains in equilibrium.
      - VMG 15y ago
        I don't think that is generally true. Historically the growth of human populations has been exponential.
swalsh 15y ago
In a somewhat unrelated idea. I've always wondered what the prospect of immortality, or longer average lifespans means in a world with rapid technological change. I'm borrowing from the idea of future shock. Young people on average, seem to be more acceptant of new technology, where older seem to be less acceptant. Additionally, from personal experience; I think younger people think about problems differently as well which leads to new developments. It makes me wonder, even if our capabilities to develop new technology are growing (Kurzweil's theory of Accelerating change) perhaps the age of both the general population, and the engineers will cause some level of impedance. Along the same lines, if a growing population requires growing technological change. And my concept is correct, that age reduces technological evolution, is it possible that it also reduces our ability to adapt, and a natural population balance occurs?
- onemoreact 15y ago
  I think it depends on the form immortality takes. Old people are less adapt at technology for two main reasons they have less free time to experiment and it takes longer for them to learn. If immortality means you never retire but the average work week is 3 days and you have the brains of a 22 year old then I don't think there is going to be much of a problem. If everyone is stuck working 40+ hour weeks with a biological age of 70+ then adaptation is going to be an issue.
  - JoeAltmaier 15y ago
    What if young people's much-lauded adaptablilty is simply, they haven't learned Anything yet so accept the 1st model they come across? That makes them appear adaptable, yet are no more adaptable than older members of society. I think to change anything substantially, you have to wait for a complete turnover - everybody has to die off, before the seeds of change can take root.
    - onemoreact 15y ago
      Young people don't become less adaptable when educated. If anything learning new things fights cognitive decline it does not speed it up.
JoachimSchipper 15y ago
Why would evolution need that? If grandpa is badly adapted, he'll starve/get eaten/etc; no need for a built-in kill switch. In fact, if there were a kill switch getting rid of it would be highly adaptive, if only because you could be around to defend your great-grandchildren. (Of course, we do die. But the explanation looks more like "growing and reproducing quicker beats longevity" than like "planned obsolescence".)
- JoeAltmaier 15y ago
  Grandpa wears out, yet competes for resources. Kill him off, more for the healthy youngsters. Certainly its selective, at the family/community level, choosing to keep more-efficient members. I also think, making grandparents less mobile means they are around the campfire teaching the youngsters. It makes sense it would be selected for in a race of communicators.
  - deleted 15y ago
    [deleted]
  - onemoreact 15y ago
    Mice and rabbits also age.
    - JoeAltmaier 15y ago
      Sure. But rats quickly die when they become less mobile or arthritic. Humans can live for decades beyond their most-productive years. Their has to be a Darwinist reason for this.
      - onemoreact 15y ago
        The Darwinist reasoning behind rates of aging goes something like this. A adult mouse has a high chance of being killed in a random year (above 20%) a Parrot has a low chance (below 3%). Maintaining a body into old age has a cost that reduces reproductive capability in a given year and a benefit of increasing the number of years of reproductive capability. There are also minimums of capability in the wild where vision and mobility link to survival rates such that there are thresholds below which rates of survival dramatically decrease. Thus, the number of healthy years in the wild relates to both the probability of an external death AND internal heath issues. For a mouse this suggests a minimum of internal maintenance for maximum reproduction where a parrot can make significant trade-offs in reproduction in order to live 10x as long and have more long term reproductive chances. However, that's in the natural setting. A pet (mouse, cat, parrot) can live slightly longer in captivity by surviving pat the point where it can find food for it's self. If you look a human vision decline people are significantly less capable of surviving on their own before they lose reproductive capability. And in that "unnatural" old age it's not uncommon for various species to have increasing reproductive issues.
TheEzEzz 15y ago
This is a group selection argument. Why do you think the group selection pressure outweighs the selection pressure on individuals (which favors organisms who can produce the most offspring, and hence favors organisms who have long reproductive lives)?
- JoeAltmaier 15y ago
  Only in social creatures, who routinely share resources at some level. Like families or villages. It doesn't have to outweight anything; its just another pressure at work. So we settle at some mean reproductive interval and some lifespan, that optimizes for all the environmental factors in play.
  - TheEzEzz 15y ago
    Imagine you're born into a tribe that has evolved to purposefully die, but you are a mutant that lives twice as long and has twice as many kids. What stops your genes from quickly spreading? All known species die of old age. This includes species that are not social and do not share resources. Group selection can not be the mechanism at play here.
    - jodrellblank 15y ago
      All known species die of old age. Except, possibly, the immortal jellyfish. http://en.wikipedia.org/wiki/Turritopsis_nutricula http://en.wikipedia.org/wiki/Turritopsis_nutricula
    - JoeAltmaier 15y ago
      All known species share their ecological niche with the rest of their members. They are also social to the extent that they court and reproduce. In your example, what stops the genes from spreading is that the entire village dies of starvation or competition with other tribes that have younger, fitter members. Its a matter of degree. Humans are social to a high degree, but possibly not as high as ants for instance. Ants eat members of the tribe that are injured, an extreme example of group-efficiency taking priority over the individual.
toumhi 15y ago
evolution is not about adaptability of a species, it's about adaptability of individuals (it's not a centralized decision taken for the well-being of a species, but rather a consequence of individuals having more chances to pass their genes than others. The lucky ones are more adaptive). If you take 2 individuals and one dies sooner than the later, the alive one will have had more chances to pass his genes, so it's not adaptive to have mechanism to ensure our deaths.
- ams6110 15y ago
  That's assuming that individuals reproduce throughout their lives, which is not the case. Reproduction typically stops before death by old age.
makmanalp 15y ago
> Longer lifespans cause fewer generations per time period This is not true though. It would be true assuming a constant population size or a single offspring. The number of children I have and the number of children my children have has nothing to do with how long we live.
- ajkessler 15y ago
  But, how long you live might affect how many children you have. Think of it this way: if you knew you had a high probability of living to 80, you might decide to have fewer offspring so that you could dedicate your earnings to supporting yourself in your later years (children are very expensive after all). Regardless of whether this hypothesis is true, clearly the number of years you live likely has some bearing on how many children you might choose to have.
Someone 15y ago
I do not think ere is need to postulate a mechanism for death. I think death is a side effect of the evolutionary competition between keeping the current organism healthy and creating new organisms. One would want both, but lack of resources forces a 'choice'. Apparently, it typically is better to create new organisms every now and then. That may just be energetically better or it may be because (in particular, sexual) reproduction allows for faster adaptation to changed circumstances
celticjames 15y ago
Food for thought: https://en.wikipedia.org/wiki/Negligible_senescence https://en.wikipedia.org/wiki/Negligible_senescence Not all animals are pre-programmed for an early death. I wonder if curve for these animals looks like the lightening bolt curve?
- reasonattlm 15y ago
  The interesting question is how you figure out those curves in a decent amount of time and cost. When you pull a lobster out of a wild population, how do you determine how old it is? Lobsters live way too long to take the sit and wait approach with a lab population, and to date there's no reliable way to determine lobster age. So that's still a real challenge, not least because there isn't all that much interest in lobster aging. http://www.fightaging.org/archives/2007/06/ageless-animals-the-lobster-edition.php http://www.fightaging.org/archives/2007/06/ageless-animals-t...
reasonattlm 15y ago
We age because the world changes: http://www.fightaging.org/archives/2011/03/we-age-because-the-world-changes.php http://www.fightaging.org/archives/2011/03/we-age-because-th... But the degree to which aging is programmed - versus simply an unhappy stochastic decay due to diminishing selection pressures in later life - is a big and ongoing debate. Some species clearly have a lot of programming going on. For example, salmon age at a rate determined by the laziness of bears near to their particular rivers: http://www.fightaging.org/archives/2007/12/bear-consumption-and-the-appearance-of-of-programmed-aging.php http://www.fightaging.org/archives/2007/12/bear-consumption-... But there are equally good counter examples for many more species that suggest the situation is that evolution sets up to win the short race, front-loading as much as it can for early success, and then the selection pressure drops off after you had your shot at reproductive success. All that front-loading produces unpleasant later consequences as things fall apart - you're not set up for the long term. The adaptive immune system is a good example of this - it's a system that could never run as evolved for an indefinite period of time. It's always going to crash and burn at some point, and that's somewhat a consequence of how it's evolved to run extremely effectively right out of the gate in early life: http://www.fightaging.org/archives/2006/12/when-and-how-does-the-decay-of-your-immune-system.php http://www.fightaging.org/archives/2006/12/when-and-how-does... For more reading on this topic, you might look into antagonistic pleiotropy - the premature optimization of the evolved world: http://en.wikipedia.org/wiki/Antagonistic_pleiotropy_hypothesis http://en.wikipedia.org/wiki/Antagonistic_pleiotropy_hypothe...
_Y_ 15y ago
I doubt it. If evolution really needed death then why does an immortal jelly-fish (http://en.wikipedia.org/wiki/Turritopsis_nutricula http://en.wikipedia.org/wiki/Turritopsis_nutricula) exist? Granted their final life stage is a polyp which creates a new young medusa, but there theoretically could be a specimen that is 7 millions years old. Either way they wouldn't need to change for number of generations.

Evolutionary theory would also suggest that we have some mechanism to ensure our deaths. Longer lifespans cause fewer generations per time period, resulting in less adaptability as a species.

VMG 15y ago

Longer lifespans cause fewer generations per time period Only if you assume the non-reproductive members are a net negative (grandparents becoming a burden)

deleted 15y ago
[deleted]
fragsworth 15y ago
Actually no, it's a little more complex than that: Regardless of reproductive lifespan, in a population that is in equilibrium (not increasing or decreasing significantly), the average number of (surviving and reproducing) children per individual is going to be 2. So supposing we could live to be 1000 years old, and still reproduce at that age, we'd have an average of 2 generations per 1000 years.
- mrbgty 15y ago
  I'm curious. What backs up the idea that the average number of children per individual will be 2 regardless of reproductive lifespan? It seems that I've seen a somewhat(?) common pattern among people who have young families and get divorced that often times have another family (+2 children) when they re-marry.
  - jowiar 15y ago
    The definition of equilibrium. Every child has 2 parents. Thus in each reproduction, every parent creates on average half a child (sounds rather morbid). Thus for the population to remain in equilibrium, each person needs to reproduce, on average, twice.
- Wilduck 15y ago
  But lifespan and reproductive lifespan are different. Suppose we could live to be 1000, but only reproduce from ages 15 to 65. Then the equilibrium number of years per generation would be right around 40.
- VMG 15y ago
  Why should genes strive for an equilibrium? Even humans for most of history tried to have as many offspring as possible.
  - fragsworth 15y ago
    It has nothing to do with genes - every population eventually hits a maximum capacity, after which it normally remains in equilibrium.
    - VMG 15y ago
      I don't think that is generally true. Historically the growth of human populations has been exponential.

swalsh 15y ago

In a somewhat unrelated idea. I've always wondered what the prospect of immortality, or longer average lifespans means in a world with rapid technological change. I'm borrowing from the idea of future shock. Young people on average, seem to be more acceptant of new technology, where older seem to be less acceptant. Additionally, from personal experience; I think younger people think about problems differently as well which leads to new developments. It makes me wonder, even if our capabilities to develop new technology are growing (Kurzweil's theory of Accelerating change) perhaps the age of both the general population, and the engineers will cause some level of impedance. Along the same lines, if a growing population requires growing technological change. And my concept is correct, that age reduces technological evolution, is it possible that it also reduces our ability to adapt, and a natural population balance occurs?

onemoreact 15y ago
I think it depends on the form immortality takes. Old people are less adapt at technology for two main reasons they have less free time to experiment and it takes longer for them to learn. If immortality means you never retire but the average work week is 3 days and you have the brains of a 22 year old then I don't think there is going to be much of a problem. If everyone is stuck working 40+ hour weeks with a biological age of 70+ then adaptation is going to be an issue.
- JoeAltmaier 15y ago
  What if young people's much-lauded adaptablilty is simply, they haven't learned Anything yet so accept the 1st model they come across? That makes them appear adaptable, yet are no more adaptable than older members of society. I think to change anything substantially, you have to wait for a complete turnover - everybody has to die off, before the seeds of change can take root.
  - onemoreact 15y ago
    Young people don't become less adaptable when educated. If anything learning new things fights cognitive decline it does not speed it up.

JoachimSchipper 15y ago

Why would evolution need that? If grandpa is badly adapted, he'll starve/get eaten/etc; no need for a built-in kill switch. In fact, if there were a kill switch getting rid of it would be highly adaptive, if only because you could be around to defend your great-grandchildren. (Of course, we do die. But the explanation looks more like "growing and reproducing quicker beats longevity" than like "planned obsolescence".)

JoeAltmaier 15y ago
Grandpa wears out, yet competes for resources. Kill him off, more for the healthy youngsters. Certainly its selective, at the family/community level, choosing to keep more-efficient members. I also think, making grandparents less mobile means they are around the campfire teaching the youngsters. It makes sense it would be selected for in a race of communicators.
- deleted 15y ago
  [deleted]
- onemoreact 15y ago
  Mice and rabbits also age.
  - JoeAltmaier 15y ago
    Sure. But rats quickly die when they become less mobile or arthritic. Humans can live for decades beyond their most-productive years. Their has to be a Darwinist reason for this.
    - onemoreact 15y ago
      The Darwinist reasoning behind rates of aging goes something like this. A adult mouse has a high chance of being killed in a random year (above 20%) a Parrot has a low chance (below 3%). Maintaining a body into old age has a cost that reduces reproductive capability in a given year and a benefit of increasing the number of years of reproductive capability. There are also minimums of capability in the wild where vision and mobility link to survival rates such that there are thresholds below which rates of survival dramatically decrease. Thus, the number of healthy years in the wild relates to both the probability of an external death AND internal heath issues. For a mouse this suggests a minimum of internal maintenance for maximum reproduction where a parrot can make significant trade-offs in reproduction in order to live 10x as long and have more long term reproductive chances. However, that's in the natural setting. A pet (mouse, cat, parrot) can live slightly longer in captivity by surviving pat the point where it can find food for it's self. If you look a human vision decline people are significantly less capable of surviving on their own before they lose reproductive capability. And in that "unnatural" old age it's not uncommon for various species to have increasing reproductive issues.

TheEzEzz 15y ago

This is a group selection argument. Why do you think the group selection pressure outweighs the selection pressure on individuals (which favors organisms who can produce the most offspring, and hence favors organisms who have long reproductive lives)?

JoeAltmaier 15y ago
Only in social creatures, who routinely share resources at some level. Like families or villages. It doesn't have to outweight anything; its just another pressure at work. So we settle at some mean reproductive interval and some lifespan, that optimizes for all the environmental factors in play.
- TheEzEzz 15y ago
  Imagine you're born into a tribe that has evolved to purposefully die, but you are a mutant that lives twice as long and has twice as many kids. What stops your genes from quickly spreading? All known species die of old age. This includes species that are not social and do not share resources. Group selection can not be the mechanism at play here.
  - jodrellblank 15y ago
    All known species die of old age. Except, possibly, the immortal jellyfish. http://en.wikipedia.org/wiki/Turritopsis_nutricula http://en.wikipedia.org/wiki/Turritopsis_nutricula
  - JoeAltmaier 15y ago
    All known species share their ecological niche with the rest of their members. They are also social to the extent that they court and reproduce. In your example, what stops the genes from spreading is that the entire village dies of starvation or competition with other tribes that have younger, fitter members. Its a matter of degree. Humans are social to a high degree, but possibly not as high as ants for instance. Ants eat members of the tribe that are injured, an extreme example of group-efficiency taking priority over the individual.

toumhi 15y ago

evolution is not about adaptability of a species, it's about adaptability of individuals (it's not a centralized decision taken for the well-being of a species, but rather a consequence of individuals having more chances to pass their genes than others. The lucky ones are more adaptive). If you take 2 individuals and one dies sooner than the later, the alive one will have had more chances to pass his genes, so it's not adaptive to have mechanism to ensure our deaths.

ams6110 15y ago
That's assuming that individuals reproduce throughout their lives, which is not the case. Reproduction typically stops before death by old age.

makmanalp 15y ago

> Longer lifespans cause fewer generations per time period This is not true though. It would be true assuming a constant population size or a single offspring. The number of children I have and the number of children my children have has nothing to do with how long we live.

ajkessler 15y ago
But, how long you live might affect how many children you have. Think of it this way: if you knew you had a high probability of living to 80, you might decide to have fewer offspring so that you could dedicate your earnings to supporting yourself in your later years (children are very expensive after all). Regardless of whether this hypothesis is true, clearly the number of years you live likely has some bearing on how many children you might choose to have.

Someone 15y ago

I do not think ere is need to postulate a mechanism for death. I think death is a side effect of the evolutionary competition between keeping the current organism healthy and creating new organisms. One would want both, but lack of resources forces a 'choice'. Apparently, it typically is better to create new organisms every now and then. That may just be energetically better or it may be because (in particular, sexual) reproduction allows for faster adaptation to changed circumstances

celticjames 15y ago

Food for thought: https://en.wikipedia.org/wiki/Negligible_senescence https://en.wikipedia.org/wiki/Negligible_senescence Not all animals are pre-programmed for an early death. I wonder if curve for these animals looks like the lightening bolt curve?

reasonattlm 15y ago
The interesting question is how you figure out those curves in a decent amount of time and cost. When you pull a lobster out of a wild population, how do you determine how old it is? Lobsters live way too long to take the sit and wait approach with a lab population, and to date there's no reliable way to determine lobster age. So that's still a real challenge, not least because there isn't all that much interest in lobster aging. http://www.fightaging.org/archives/2007/06/ageless-animals-the-lobster-edition.php http://www.fightaging.org/archives/2007/06/ageless-animals-t...

reasonattlm 15y ago

We age because the world changes: http://www.fightaging.org/archives/2011/03/we-age-because-the-world-changes.php http://www.fightaging.org/archives/2011/03/we-age-because-th... But the degree to which aging is programmed - versus simply an unhappy stochastic decay due to diminishing selection pressures in later life - is a big and ongoing debate. Some species clearly have a lot of programming going on. For example, salmon age at a rate determined by the laziness of bears near to their particular rivers: http://www.fightaging.org/archives/2007/12/bear-consumption-and-the-appearance-of-of-programmed-aging.php http://www.fightaging.org/archives/2007/12/bear-consumption-... But there are equally good counter examples for many more species that suggest the situation is that evolution sets up to win the short race, front-loading as much as it can for early success, and then the selection pressure drops off after you had your shot at reproductive success. All that front-loading produces unpleasant later consequences as things fall apart - you're not set up for the long term. The adaptive immune system is a good example of this - it's a system that could never run as evolved for an indefinite period of time. It's always going to crash and burn at some point, and that's somewhat a consequence of how it's evolved to run extremely effectively right out of the gate in early life: http://www.fightaging.org/archives/2006/12/when-and-how-does-the-decay-of-your-immune-system.php http://www.fightaging.org/archives/2006/12/when-and-how-does... For more reading on this topic, you might look into antagonistic pleiotropy - the premature optimization of the evolved world: http://en.wikipedia.org/wiki/Antagonistic_pleiotropy_hypothesis http://en.wikipedia.org/wiki/Antagonistic_pleiotropy_hypothe...

_Y_ 15y ago

I doubt it. If evolution really needed death then why does an immortal jelly-fish (http://en.wikipedia.org/wiki/Turritopsis_nutricula http://en.wikipedia.org/wiki/Turritopsis_nutricula) exist? Granted their final life stage is a polyp which creates a new young medusa, but there theoretically could be a specimen that is 7 millions years old. Either way they wouldn't need to change for number of generations.