Is there an evolutionary advantage to death?: Philosophy Forums

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Is there an evolutionary advantage to death?

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Is there an evolutionary advantage to death?

jsawvel
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Posted 10/03/09 - 10:55 AM: Subject: Is there an evolutionary advantage to death?	#1
I was just thinking how some turtles live to be 500 years old and house flies might just live for a couple days. Obviously all species aren't aiming for immortality. Are there evolutionary advantages for a species by dieing at a set age? And do WE die because we are "designed" to die, or just because our body "wears out."

Arkady
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Posted 10/03/09 - 11:15 AM:	#2
This is a very interesting question. Richard Dawkins addresses thinking on the topic in 'The Selfish Gene' and W.D. Hamilton had a number of ideas on the subject. Possibilities: 1) Aging and death were actively selected traits. Possible reason? To free up resources for younger (and thus more fertile) cohorts. 2) Natural selection doesn't "care" about what organisms do post-reproductive age, and as a result, our bodily repair mechanisms break down in old age because there was no selective pressure to actively maintain them. So, this would be a sort of "passive" degradation of traits, like a house that gradually falls apart under the influence of entropy when it's not actively maintained. #2 may be begging the question because it could be prudent to ask why we even age to a point where we are "post reproductive". There are doubtless more options; I'm just throwing out the 2 options which most readily came to mind.
"Sit down before fact like a little child, and be prepared to give up every preconceived notion. Follow humbly wherever and to whatever abyss Nature leads, or you shall learn nothing." -T.H. Huxley

Aceedwin
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Posted 10/03/09 - 12:09 PM:	#3
Evolution is based on death. But it's tricky to make the same connection the other way, hm. I personally support #1 above. In an enviroment where the most advanced generations are the only ones left standing, the evolutionary cycle goes faster. It's a bit of a circle, is it not? Evolution produces death so that death can produce evolution.
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Noumenal1
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Posted 10/03/09 - 12:46 PM:	#4
Arkady wrote: 2) Natural selection doesn't "care" about what organisms do post-reproductive age, and as a result, our bodily repair mechanisms break down in old age because there was no selective pressure to actively maintain them. So, this would be a sort of "passive" degradation of traits, like a house that gradually falls apart under the influence of entropy when it's not actively maintained. #2 may be begging the question because it could be prudent to ask why we even age to a point where we are "post reproductive". #2) This answer seems rational to me (good post Arkady). Perhaps we evolved with a metabolism 'geared' more for growth than long term maintenance. Each organism of course evolves with a metabolism rates that differs, maybe faster rates result in earlier death (?). #1) I have to reject this answer though. Evolution does not think ahead like this. Edited by Noumenal1 on 10/03/09 - 12:56 PM

keda
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Posted 10/03/09 - 01:16 PM:	#5
I think #2 can be questioned because you can influence the survival of your children, grand children and other relatives i.e. kinship selection.
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mutemaler
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Posted 10/03/09 - 01:20 PM:	#6
jsawvel wrote: I was just thinking how some turtles live to be 500 years old and house flies might just live for a couple days. Obviously all species aren't aiming for immortality. Are there evolutionary advantages for a species by dieing at a set age? And do WE die because we are "designed" to die, or just because our body "wears out." Both the turtles living 500 years and the hourse flies several days 'work', they are both successful in that way. But I think the very first thing you should do is remove the temptation to inject words like purpose and design into evolution. Instead say that there is variance, in effect things more or less just get tried out, some persist and some don't (either for reasons of adaptibility or just sheer luck, so remove the 'survival of the fittest' also from the discussion, replace it with 'just barely fit or better'). What occurs to me first of all is that there is likely a rough correlation between longevity and the rate of metabolism, that would speak for there being just so much life in the basics of living material. And there have also been experiments where longevity was increased through a mild form of starvation. It seems possible at least that longer living beings (who then also evolve slower) might be more tolerant to change in the environment, and the shorter living might be less tolerant to changes in the envirnment but are able to evolve somewhat quicker to adapt to it. The advantage to dying period should be obvious (evolution requires it). So there might not be a an evolutionary advantage to dying at a certain age (or it all balances out), but there could be an advantage period to dieting. Edited by mutemaler on 10/03/09 - 01:29 PM

Noumenal1
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Posted 10/03/09 - 01:24 PM:	#7
jsawvel wrote: ... do WE die because we are "designed" to die, or just because our body "wears out." Rather than there being any advantage in evolutionary terms to have been "designed" to die, I would rather think that there was simply no advantage in living perpetually (well past reproductive age), in evolutionary terms.

Hamandcheese
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Posted 10/03/09 - 01:45 PM:	#8
Natural Selection only cares about genetic immortality. After your genes are passed on (normally well before 30 on the Savannah) and your offspring are raised (normally well before 50) there is no pressure against death, aging, cancers, and senility. Not coincidentally, human cognitive ability starts declining at 30, and menopause kicks in around 50.
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Arkady
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Posted 10/03/09 - 01:47 PM:	#9
Noumenal1 wrote: Perhaps we evolved with a metabolism 'geared' more for growth than long term maintenance. Each organism of course evolves with a metabolism rates that differs, maybe faster rates result in earlier death (?). Yes, this is correct. Interestingly, mammals across different species have the same number of heartbeats in their life. So, for instance, a field mouse has the same number of heartbeats in its lifetime as an elephant. But, as the mouse's heart beats much more quickly, its lifetime is shorter. The metabolisms of small animals do run faster than those of large animals. This is at least partly due to physics: small animals have a larger surface area/volume ratio than larger animals, and thus lose heat more rapidly to their environment, necessitating a faster metabolism. There is in fact a general trend of different species increasing in average body size the further they are from the equator. Noumenal1 wrote: #1) I have to reject this answer though. Evolution does not think ahead like this. No, it certainly doesn't. But, it doesn't need to in order to "design" complex anatomical traits or behaviors. In order for #1 to obtain, those organisms who died earlier in their post-reproductive phase would have more successful offspring (and grand-offspring) because, say, their deaths freed up more resources for the offspring. Thus, that genetic propensity to age and die in their post-reproductive life would live on in their offspring, outcompete other variants, and be propagated through the generations until it becomes "fixed" in a population. Noumenal1 wrote: #2) This answer seems rational to me (good post Arkady). Thanks, Noumenal! But, in the proudest philosophical tradition, I'm going to tear down my own argument. I think #2 is circular because it essentially explains why organisms age by saying that they age. Consider: Premise 1: Organisms age. Premise 2: At some point, organisms age past their ability to reproduce. Premise 3: As natural selection is "blind" to the post-reproductive phase of an organism's life, bodily repair mechanisms are no longer actively maintained. Conclusion: Therefore, organisms age and die. One of the premises contains the conclusion, i.e. the argument is circular.
"Sit down before fact like a little child, and be prepared to give up every preconceived notion. Follow humbly wherever and to whatever abyss Nature leads, or you shall learn nothing." -T.H. Huxley

wuliheron
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Posted 10/03/09 - 02:08 PM:	#10
It matters in part what you mean by death. For example, there are single cell organisms that reproduce by parthenogensis and are for all practical purposes identical. Likewise, viruses are considered dead unless they inhabit a cell because they don't reproduce, metabolize, or move around outside of a cell. Some even consider viruses to be nothing more than interesting chemical reactions rather than alive. Although the argument that after we reproduce we become disposable for evolutionary purposes has been around for awhile, more recent studies have shown that grandparents (especially grandmothers) can play critical roles in helping to raise their grandchildren. In addition, the record number of children sired by the same father is over 450 and males can reproduce well into their eighties. This then begs the question as to how exactly much death could promote evolution among human males. Epi-genetics is a new science that shows that how we live our lives as individuals has a greater impact on evolution than was ever suspected. For example, if your grandparents starved at some point in their lives before conceiving your chance of becoming diabetic late in life becomes almost certain. Thus there may be a genetic balancing act taking place where the benefit of living long enough to care for newer generations is balanced against health problems that can be inherited. Flys and roaches don't rear their children, they lay their eggs and walk away or even die on the spot. The vast majority of their progeny die from diseases because they have virtually no immune system and it is a rare bug that dies of old age even if they only live for a month. Reptiles have many of the same problems with perhaps eighty percent of them dying from disease and the extremely rare turtle living to be hundreds of years old. Many species of bugs and reptiles have not changed significantly for hundreds of millions of years, so it is difficult to argue that death has much of an evolutionary impact on their species. The human genome is extremely complex and, as yet, little understood. It seems likely with what little we do know that death may play a part in our evolution, but exactly how significant it might be, if at all, is debatable. Before we can answer that question with any authority it seems to me we first need to be able to answer just how significant a role our average lifespans play. We are no longer wild animals whose genes are subject to whatever our enviroment throws at us. If we were, I would have died many decades ago from a simple case of appendicitus and would never have had children.

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