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Comment by srean | Hacker News Reader

To survive natural selection the gene must give the animal some reproductive advantage. I can understand that promoting longevity beyond the reproductive stage of one's life cycle affords no such benefit. But one still has to account for the fact that the lack of the gene appears to increase the survivability in the reproductive pahse as well. Something more must be going on.

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Strictly speaking, it must give the _gene_ a reproductive advantage, not necessarily the animal. Often, these two advantages are aligned. But they need not be. This is the case in kin altruism. And this is also, why "promoting longevity beyond the reproductive stage of one's life cycle" affords sometimes very much such benefits. Example: grandparents can help raising their children's children (and their children's children's children ;)). Kin altruism becomes even more apparent in ants (or other social animals). Worker ants or bees are pretty much infertile but they help a lot.

It should be noted that the difference is much more extreme for ants than it can be for mammals due to a genetic quirk where a female ant shares 50% of her genes with her children and 75% with her sisters. (Therefore having more sisters is better than having children.)

Still there are mammals that live eusocial. The naked mole rat comes to mind.

> To survive natural selection the gene must give the animal some reproductive advantage.

Most probably, but not necessarily.

A gene can be present without being useful because it is linked to another gene that is itself useful; or it can be a leftover from an earlier moment of evolution where it was useful, and then it ceased to be useful but there was never an evolution pressure strong enough to have it disappear.

In summary, just because a gene is present and active does not mean it's useful today.

Not necessarily. The mutation could have survived for any number of reasons including genetic drift. As long as it didn't kill the organism right away there wouldn't be significant negative pressure to get rid of it.

Perhaps not having the ability to regenerate leads to more cautious behaviour, avoiding life threatening situations to a much greater extent? Puzzling...

I don't think the ability to regenerate means that losing a limb doesn't hurt...

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