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Happy 200th birthday, Charles Darwin!

Imagine a world in which senescence is eliminated, so that death rates do not increase with age but remain throughout life at the level for eighteen-year-olds, that is, about one per thousand per year. Some people would still die at all ages, but half the population would live to age 693, and more than 13 percent would live to age 2000!" -- Nesse and Williams (1994) Why we get sick: the new science of Darwinian medicine
Although Darwin's ideas are increasingly influential (at least among scientists), Darwin himself is dead. In a world without senescence, he might still be alive. In The dawn of Darwinian medicine. Q. Rev. Biol. 66, 1-22 (1991), Williams and Nesse offered the standard evolutionary explanation for aging:
Because the force of natural selection is stronger at earlier ages to which larger numbers survive, a gene that causes substantial morbidity and mortality during the tail end of the expected life span in the wild may nonetheless be favored if it has even minor earlier benefits.
The most important of these "earlier benefits" appears to be more reproduction earlier in life. One of my students came up with some interesting ideas about the implications of this tradeoff between reproduction and longevity, which I will discuss here once our paper is published.

Comments

I could see genes for senescence being selected for by reducing competition for those at the peak of reproductive capacity and ability to care for the young (in those species that give parental care).

Hi, just wanted to let you know that your blog has been extremely useful and interesting. This thanks is coming from a college student in an evolutionary course in Philadelphia PA :)

Dave, how would senescence of adults with a particular allele preferentially benefit others with the same allele?

Dave, how would senescence of adults with a particular allele preferentially benefit others with the same allele?

It wouldn't. However, I could see those without the senescence alleles taking up resources that their children and grandchildren could use, while those with the senescence alleles would not.

Dave,
My point was that, in many species, benefits (from grandparents sparing resources by dying) would often be equally available to unrelated individuals with different alleles. There may be some exceptions, but "sparing resources for the next generation" doesn't seem like a generally applicable explanation for senescence.

I think you're right. My scenario would require some fairly specific circumstances.

I do remember (vaguely) a paper by Hamilton on the evolution of senescence. I'd probably do well to go back and re-read it.

Thanks for helping me sharpen my thinking!

Dave,
There could be such conditions; it's just not a general explanation.

Hamilton, W. D. The moulding of senescence by natural selection. Journal of Theoretical Biology 12, 12-45 (1966).

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