Jayjay

I think that what malookiemaloo is asking is, how can "dying" possible be a beneficial feature that is selected for? I can imagine that in a population, having lots of old geezers around might be detrimental to the gene pool (e.g the ones who survive don't do it by virtue of their genes, but rather because they've been around for a long time), but I'd appreciate it if someone more knowledgeable than me could provide a better example.

malookiemaloo

Thanks monkeybot.

I'll look at these websites.


M

GunnerJ

Adapting to environmental conditions is how a species survives.

Natural selection is one of the core mechanisms by which evolution acts. Other mechanisms of note: Mutation, genetic drift, genetic flow.

Natural selection is the process by which alleles in a gene poll increase or decrease in frequency depending on the survival (that is, procreative) advantages or disadvantages, repecitvely, that they impart on a species. To ask "how could death evolve" imples that soemwhere along the line there was a gene that made organisms die of old age and a gene which allowed organisms to be clinically immortal, and the immortality gene was selected against. This may not be the case. As far as I know, aging is caused by degenration of the DNA in cell lines as the divide.

There was a thread on this exact subject here, I will try and find it.

Edit: Here it is.

"de-evolution"

nogods4me

of course natural immortality would be a detriment.
competition for limited resources is one of the engines that drives natural selection.
with a bunch of older organisms around, especially if they were beyond the age of fertility, all they would do is consume resources. that is a bad thing, evolutionarily speaking.

Peez

There are probably trade-offs with many traits that evolve. What I mean by that is that many traits are not all good, there are likely down-sides to each trait. Thus natural selection favours a trait when the advantages to that trait outweigh the disadvantages. As has been pointed out, even if aging did not occur the great majority of organisms would die relatively early anyhow. This means that any genes that confer greater lifespan (less aging) will not provide much benefit to the great majority of individuals, and if there is any trade-off (e.g. decreased growth rate early in life) then natural selection would likely work against long lifespans.

There may also be constraints: even without any specific aging mechanism, the body tends to accumulate damage here and there. By the time we are "old," the damage can be significant. It may simply be very difficult to avoid aging.

Peez

gcameron

I seem to recall reading in one of Dawkins's books the idea that harmful mutations can accumulate later on in an organism's life because, once they have reproduced, there is less selection pressure to get rid of those harmful mutations (which would result in what we call aging). This is basically the same idea as Monkeybot's exploding-after-mating animal, and of course in the animal kingdom we do see examples of animals for whom mating = death -- unless stories about praying mantises etc. are exaggerated?..

You might argue that the genes of an organism that keeps reproducing for a million years would be selected in favor of an organism that reproduces for only one year; but doesn't evolution favor shorter generation times? (I.e. an immortal organism that kept spreading its genes would eventually get left in the dust by the descendants of its shorter-lived neighbors.) I suppose this gets into higher-level evolution, the evolution of evolvability, etc. Rather heady stuff.

gcameron

Also, though, to suggest that death evolved seems to imply that there was a pre-existing state of immortal organisms. Even barring death by accident, predator, disease, etc., does simple wear-and-tear factor in? I.e. an animal's body will start to break down from use unless specific regenerating capabilities are put into it. But then of course some animals *can* regenerate limbs etc... and we can all regenerate at least as far as run-of-the-mill healing.

Doubting Didymus

That story is so much fun, and my cold and heartless facts so grey and dull, that I would have your story be true and my own version deposed.

Unfortunately, the cannabilism exhibited by female mantids is simply a side effect of them being improperly fed in captivity. No full-stomached female mantid has ever been observed to resort to eating hubby. The fact that compulation becomes faster when the males head is removed is a coincidence, but that is what originally inspired the hypothesis.

Kind of sad, really. Next I'll be telling you that there is no such thing as a venus flytrap.

Lobstrosity

Malookie, think about what would happen if organisms didn't die. Organisms in general live within an ecological niche of finite size comprised of finite resources. If the organisms were to reproduce at a much higher rate than they died, they would soon fill their niche to capacity. They would proceed to deplete their much-needed resources over time, which would lead to mass starvation (or many other problems that accompany overpopulation). Evolution cannot function well in a population that undergoes rapid booms and busts, for each bust severely depletes the gene pool and tends erase evolutionary progress. Furthermore, if a bust is severe enough, the population risks extinction.

There is some evidence that death is an evolved property of life (for example, aging might arise from the telomeres that cap our chromosomes). After all, there's no fundamental law of physics that requires an animal to age, to get weaker with time. It seems like aging is something we organisms developed so that there would be room for newer generations. Death allows for reproduction, and reproduction allows for evolution. It's an intimately-linked cycle that proves beneficial to the species even though it may not be the best thing for each individual organism of that species (i.e. the individual may not be "happy," per se, about dying, but its sacrifice allows the species as a whole to evolve, adapt, and survive on).

Proctors_Gambit

I would see it as survival of the population over survival of the individual unit.

The species would function best if it keeps it's median age in its fittest years of life.

Why would any species want a majority of old, less fit individuals in the group using up resources and space when they are not able to protect the population against predators for example.

Keeping a limit on each individual units age is very important in terms of survival of the species as a whole.

My thoughts, but then, I studied computers in school.

-Gambit