An alert reader has written me about a statement I made in WEIT:
You write that “a gene that knocks you off after reproductive age incurs no evolutionary disadvantage.” And you go on to say that selection would not favour genes that helped survival after reproduction has finished. “One example would be a gene that helps human females survive after the menopause.” I understand and accept this point. But could there be an exception (in theory) as follows? If women were giving birth right up to menopause, they would need to survive after menopause to bring up their last children. Also, if a woman who survived post-menopause helped her daughter to bring up her grandchildren and had the effect of improving the survival rate of those grandchildren, wouldn’t her “live longer genes” then get passed on?
The reader is absolutely right–I glossed over the nuances of this idea in the interest of space, and probably shouldn’t have. Indeed, a woman will be selected to live until all the benefits she can confer upon her children (the most important being maternal care) have already been bestowed, and that means staying alive until she has brought up all her offspring. To the extent that children are grown and independent before menopause, selection will be very small against a gene that bumps mom off. That is, of course, unless she can help her grandchildren grow up, for in that case she is still contributing to the survival of her own genes in her offspring’s offspring. So there are exceptions to what I said. Let me then rephrase my statement to say that “a gene that knocks you off after you’ve made all possible contributions to rearing related individuals incurs no evolutionary disadvantage.”