I thought of this question reading the various debates on evolution, and decided I should post it seperately rather than change the subject.
Why the heck do animals get old and die? (I mean a biological evolutionary why, not a theological why)
What I’ve read seems to indicate that biologists believe aging is controlled by genetics, meaning that either we’re actively programmed to self-destruct, or else for some reason there’s been no selective pressure for genes to ensure perpetual youth.
In terms of pure natural selection, you’d think that an immortal organism that could keep reproducing until it finally got eaten would leave more descendants that an organism that lasted just so long and then self-destructed. So why die?
Some WAGs:
[list] [li]Keeping an old organism alive is more “expensive” than creating a bunch of new ones []Old organisms compete with new ones. Fewer new organisms means less adaptability. []There’s something biologically impossible about keeping a multicell organism together forever. []Brains wear out []Staying alive requires exverything to work. Reproducing requires only the reproductive system to work []I’ve heard that cells can only split so many times, although why gametes are exempt from this (and they must be), I don’t know []It’s easier to reproduce than to fix all the problems that organisms develop If living beyond a certain age is highly unlikely because of disease, predation, etc., then it makes sense to devote resources towards reproduction rather than keeping the body together on the slim chance that it will still be needed several decades from now.[/li]
-Ryan
" ‘Ideas on Earth were badges of friendship or enmity. Their content did not matter.’ " -Kurt Vonnegut, * Breakfast of Champions *
It would be much easier to evolve better reproduction skilll than better longevity. To have more offspring, alll a species may need could be longer claws, stronger legs, stripier skin, etc. To live longer, the organism would have to change its cells on a more fundamental level.
In the wear and tear of daily life, hundreds (probably more, but I don’t want to be wrong in my guess) of cells die. They are sequentially replaced by new ones. (Yes, even nerve cells, although on a much slower timescale). Cells in most multicellular organisms have special tags on the ends of the DNA (I think they’re called telomeres, I may be wrong). The designed purpose of these tags is to protect the ends of the DNA (Appaently dividing is strenuous on the integrity of the chromosome). So each time the cell divides, rather than lose a chunk of the important information, a piece of the telomere is lost. Since the telomeres have a finite size, eventually it’s all going to be gone. At that point, the cell can no longer safely divide and so it stops. Once the cell stops dividing, damage can’t be repaierd. Decay really starts to set in, and the animal dies.
On a side note, research is currently being done to stop telomeres from breakign off. They’ve been able to keep a piece of foreskin dividing for two years in a culture, much longer than it naturally should have. Unfrtunately, cells that divide infinitely increase the risks of cancer, so there are still a few kinks to work out.
It was a way to get you off your asses and DOING something. I got tired of hearing:
“I’ll do it tomorrow or next week or in 5000 years. Hell, I’ve got forever.”
My WAG: The older creature reproducing will give birth to a creature whose chromosomal integrity is far more questionable. Therefore reproductive age tends to be limited. And although the ability of a creature living past reproductive age could be selected for (see Woman: An Intimate Geography / Natalie Angier), I figure there is less and less of that kind of effect as one’s children’s children cease to be dependent, and after that there is no reason for more prolonged lonvevity to be passed down and inherited.
However, if you don’t die, you don’t need to reproduce. Your genes will survive in you, without the messy and not entirely accurate middle-man of mating.
What do you mean, “need to reproduce”? No one “needs to reproduce”, but creatures that do reproduce are much better represented in the gene pool than ones that don’t. If you live forever, you’ll be better represented if you reproduce. If you don’t live forever, you’ll be better represented if you reproduce. Either way, it’s better to reproduce. But there’s no assurance that you will live forever; eventually death will catch up with you. I guess reproduction is sort of life’s way of being more of a moving target to death.
-Ryan
" ‘Ideas on Earth were badges of friendship or enmity. Their content did not matter.’ " -Kurt Vonnegut, * Breakfast of Champions *
What’s important is whether you die before being able to reproduce, so as long as your natural lifespan allows that to happen, it’s good enough. What happens to you after you reproduce is not of much consequence, even if you live until umpty-two bazillion years of age due to some quirk mutation. As long as you get to the point where you can and do reproduce, that’s all that counts. Extending the natural lifespan doesn’t help when your problem is not being eaten by whatever preys on your species when you haven’t gotten to reproductive age yet.
not really. As a man ages, the number of spunky sperm decreases. An older man’s sperm is more sluggish, and has more “duds” than a younger man’s, and more likely to have defective genes. The older he gets, the less viable sperm he produces.
This seems like another instance of ascribing some “purpose” to evolution. There may be no reason for death other than the fact that natural selection will never beat entropy (if I’m using that term correctly.)