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Life expectancy for human has significantly increased during the last century or so. We all know that there are many reasons that are not linked with "evolution", but I am wondering if such change in life expectancy has been observed "naturally" (not counting animals in zoos or domestic ones). Does evolution favor long lasting individuals?

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The prolonged life expectancy over the last century can be explained by better medicine, hygiene, food and better working conditions. It is not connected to evolution (which generally takes place over long time periods, not just over the course of only three generations). The same is observed for zoo animals. –  Chris Feb 23 at 21:03
    
There is life extension work with animals, but just as Chris says its more about changing conditions or finding mutations that change life expectancy. –  shigeta Feb 23 at 21:19
    
@Chris thanks for your comment. I've tried to edit my question to make it more clear. I know that it is not due to evolution for humans and zoo animals, but I was wondering if it had been observed for some species as a consequence of the "survival of the fittest". A millenimum was maybe to short (though it is more than 3 generations), but I guess that it is difficult to observe, so maybe it can only be shown for species with small longevity. –  radouxju Feb 23 at 21:21
    
@shigeta thank you for your comment. Are the mutations that change life expectancy beneficial to the population ? I mean, long life expectancy can reduce the possibility to adapt quickly, so this can make the species more vulnerable to, e.g. habitat change, but does it provide any advantage. –  radouxju Feb 23 at 21:30
    
The answer kinda depend on what you'll accept to be an observation. It seems that you want an observation where we measured the mean life expectancy of a species over a (very) long term and find out that it is increasing. Such study very probably does not exist for obvious reasons. But you might be interested in some key mutations that changed life expectancy and on proof that this mutation rises through time (selective sweep) or you might be interested to know more generally about life history traits or to seek for correlations between life expectancy and some ecological traits. –  Remi.b Feb 23 at 21:33

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As far evolution is concerned, there is no benefit whatsoever in having long lived individuals. Evolution only "cares" about individuals while they are capable of reproducing. Survival past the maximum age of reproduction is irrelevant from the evolutionary point of view since it does not make you any better at reproducing, and therefore your genes will not be selected for.

This is highlighted by the various species that die to give birth to or feed their young. One of my favorite examples is the giant pacific octopus (Enteroctopus dofleini) whose females lay their eggs and then die, leaving their body to feed the emerging young.

Now, a mutation that makes an individual both longer lived and capable of reproducing at a greater age could well be selected for. It just always needs to be combined with the ability to reproduce. By itself, dying older will confer no selective advantage unless it is combined with producing more offspring.

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The life expectancy of an animal (or anything) is just one aspect of how 'fit' they are to survive. having them live too long can be a detriment to the species.

There is no simple 'better/worse' relationship of fitness to life expectancy. In simple population models predators which reproduce to much or live too long will tend to eat all the prey and starve to death for instance.

The most famous example of life extension molecular biology is the discovery of a 'Methuselah worm' by Cynthia Kenyon about 10 years ago. With a single mutation these C. elegans worms can live about 50% longer, and seem to be pretty energetic while doing it.

It would be interesting to put some of these Methuselah worms into a wild population and see what happens to their life span as they interbreed. C elegans is a highly programmed organism - each cell has a predetermined plan for development and lifespan, which made this worm relatively easy to find.

For human beings (the best studied animal on Earth) there is no simple genetic relationship to longevity for most of us, but there appear to be some simple combinations that are responsible for the oldest living humans:

a genetic model comprising 150 SNPs in order to compute the predisposition of an individual toward EL. Their model successfully predicted exceptional longevity in a different sample of centenarians (individuals that live to age 100) with 77 percent accuracy. This demonstrates that EL is strongly associated with complex combinations of genetic variants.

So for humans this experiment has sort of been done. Longevity phenotypes are possible but don't overall convey a reproductive advantage and so while they hang out in the gene pool, they aren't enough of an advantage to reproduction to be spread about widely...

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