I know death and cancer doesn't hurt humans' reproductive success. It's not helping either.
Why do we die? Why dying humans (all of us) are common? What's the point of dying?
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23$\begingroup$ Not everything has an evolutionary advantage... $\endgroup$– nicoCommented Mar 20, 2012 at 6:55
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4$\begingroup$ Cancer does hurt human's reproductive success; and evolution does fight with it. $\endgroup$– Piotr MigdalCommented Mar 20, 2012 at 8:15
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4$\begingroup$ Most cancers are post-reproductive, so fitness (strictly speaking) is 0 at that point. $\endgroup$– kmmCommented Mar 20, 2012 at 16:04
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2$\begingroup$ @nico is correct, and he's not likely saying so with any religious zeal... for example, genetic drift is a powerful evolutionary force that has no obvious "advantage" per se. I've edited your title to remove that suggestion. but +1 anyway since it's an interesting question. $\endgroup$– hello_there_andyCommented May 8, 2014 at 19:32
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1$\begingroup$ If there was no death,the experienced older people among animals and humans would be more successful ,so the was no progress chance for the young and the animals couldn't transfer their gen and there wouldn't happen any mutation. $\endgroup$– user14640Commented Feb 28, 2015 at 20:44
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6 Answers
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Death is not only for humans. All 'complicated enough' organisms die (with a notable exception of Hydra, though you may argue when it comes to the complexity). It is is easier to create a new organism from scratch than to repair both internal factors (free radicals, metabolic by-products, ...) and external (physical damage, exposure to toxins, ...).
Underlying causes of death actually can be evolutionary beneficial. For example, shortening of telomeres offers protection against cancer (on a cellular level), but also bounds lifespan.
So actually they may be evolutionary competition (within the same species) of young and old. Mutations helping young but harming older may be preferred to the opposite ones.
answered Mar 20, 2012 at 8:13
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Who is to say that having living Humans isn't hurting our reproductive success? Older non-reproducing humans cost the human network valuable resources and take up a sizeable portion of our living niche. Metabolically unstreamlined aged organisms are certainly not the most efficient and could potentially get in the way of better suited young'uns.
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9$\begingroup$ It's naive group-selection argument. Like "I'd sacrifice myself when I get old so that others could produce more children". But if one would live longer and help his own grandchildren - he would spread his genes better even if it would hurt the society. $\endgroup$ Commented Mar 21, 2012 at 6:41
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$\begingroup$ @MartaCz-C: how does helping grandchildren spread genes? The only way for an old person to continue spreading his/her own gene is to have kids which would actually be bad. $\endgroup$– nicoCommented Apr 6, 2012 at 6:12
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2$\begingroup$ @nico if person X have even 15 children but non of them have their own children through their lifespan, then genes of person X did not spread at all. One of measures of fitness is number of grandchildren. $\endgroup$ Commented Apr 6, 2012 at 9:28
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$\begingroup$ @MartaCz-C: sure, but my question is about "helping his own granchildren". The fact of helping them in no way means you are spreading your own genes. The fact of having granchildren means you spread your own genes in the past which... well is the purpose of reproduction. $\endgroup$– nicoCommented Apr 6, 2012 at 10:29
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4$\begingroup$ @nico Helping your relatives spread their genes is equal to spreading your own genes (if you multiply your effort in helping others by the percentage of consanguinity). That's what I mean but maybe I use wrong terminology. $\endgroup$ Commented Apr 6, 2012 at 14:29
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From a systemic point of view, if we wish to evolutionarily induce our descendants (descendants of the current human race on the whole) to live longer lives, we would need to pro-create later.
If the whole of human race enforced a statute that prohibits pro-creation before the age of 40, then two pronged dynamics would happen
- only adults fit enough to pro-create after 40 would produce off-springs.
- only off-springs born to parents older than 40 who are fit enough would survive.
Since, there is a high tendency of abnormality and low survival of off-springs born to parents of older ages, absence of resource contention and genetic dynamics would encourage the initial propagation of the rare few fit off-springs.
Hence, unnatural "natural selection" would encourage the propagation of humans of longer life-spans. Perhaps, a natural disaster or viral outbreak could discourage humans from pro-creating before age 40. Perhaps, high rates of abortion. So long as the human race does not die out due to such restrictions. Perhaps, to the satisfaction of conspiracy lovers, a secretive organisation carries out a plan every 100K years to raise the bar for child-bearing age.
Therefore, it might be less of a question of advantage and more of the effects of motivation. That current status where
- high motivation for humans to pro-create early in life.
- low motivation for humans to have more children as they wise-up by being tired of raising kids too early.
Therefore, since no such secret organisation exists, there is infinitesimally little motivation for the existence of a "super-virus" type of humans to exist.
There is no motivation for super-humans to exist, because the distribution of life-spans have crowded out the food and survival resources of any possible primeval super-human.
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$\begingroup$ Do you have proof of your first part in your answer? I know it holds for fruit flies, but that doesn't mean it holds for humans. $\endgroup$ Commented Jan 22, 2020 at 3:12
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There is no evolutionary advantage to dying.
So you question should be rephrased as to why organism die at all? Why hasn't evolution come up with an immortal animal that lives forever?
Well nature has actually done that https://en.wikipedia.org/wiki/Turritopsis_dohrnii Behold the immortal jellyfish.
So if we do have immortal jellyfish.. why aren't there immortal mice?
A possible answer is because mice get eaten by cats (and wolves, foxes, owls, toads, humans, etc) The idea goes like this... there is no point having genes that makes you immortal if the probability of you being eaten within 1 year approaches 100%. In fact, in such a situation, you would want genes that will allow you to have as many babies as possible before that one year is up, even if those genes result in your death (ie cancer from cells that are growing too fast in that rush to be an adult, heart problem, muscle degeneration, poor immune system.. because the body has redirected all energy from repair to reproduction). Such a trade off is worth while, as you aren't going to be alive long enough to see the downside of those bad genes.
So if this idea is correct... if an animal has fewer predators (or none at all), the animal would live longer. And yes, we actually do see such examples.
A famous example are the Opossums of Sapelo Island. The Possums were isolated on a predator free island 9000 years ago and now live 25%-50% longer than their mainland cousins. The difference is hereditary.
Another possible example is that between bats and mice. Both are small animals of similar weight. And in general the smaller the animal, the faster it breeds and the shorter its life span. Bats are a noted exception from this the rule. Bats live a very long life span or their mass. Lifespan in the wild rangers from 10 years to 40 years depending on species. Compare that to 1 year for a mouse. The difference? Not metabolism... Not mass.. Not climate. But predators. Mice have many predators. Bats very few.
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One key concept to bear in mind is "mutational load". Over time, individuals accumulate mutations - for example, older fathers pass on more mutations than younger ones. Undesirable mutations need to be removed by natural selection each generation at at least the same rate as they accumulate, or a "mutational meltdown" occurs. The length of time between generations needs to be set so that the number of mutations purged by deaths is equal to the number that are introduced by mutation. Here is a rather interesting study providing some evidence for this point of view.
Note that infertility is "lethal" in genetic terms, so this concept in and of itself does not explain why a woman who passes menopause needs to die at any age. It seems easy to add further speculation here, so I'll leave that to the reader.
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The evolutionary explanation is quite simple. Without death, evolution couldn't take place in the first place at all.
Who knows that jellyfish are immortal? Did they continuously evolve from one cell (without reproduction)? I don't think so. Who knows if today present jellyfish were already alive 1000 000 years ago (i.e. without parents)? I think this is the case for any living creature.
That's why telomeres get shorter and shorter when growing older. In the case of cancer, these telomeres stay the same with each division of the parent cell, so it grows wildly. Which all species would probably do so too.
