Thank Jumala for Finnish record keeping!

By Razib Khan | July 16, 2007 2:03 pm

You might not be able to do controlled experiments on humans for evolutionary biological purposes (not only is it unethical, the leisurely rate of human reproduction doesn’t make it viable for cranking out Ph.D.s), but you can analyze our pedigrees! Scientific American has a long article, What Finnish Grandmothers Reveal about Human Evolution, about Virpi Lummaa’s research program. It’s a “sexy” one, I’ve blogged her research several times, it has pretty deep appeal, focusing on humans & evolution. For you religion haters out there, I do have to point out that it is enabled by the thoroughness and time depth of Scandinavian record keeping under the auspices of the Lutheran Church and its baptismal and death records. In any case, this part is new to me:

Lummaa has now turned her attention to the effect of grandfathers on grandchildren. If grandmothers improve survival odds, what do elderly males contribute? “If anything there’s a negative effect,” she says. This could be because of the cultural tradition of catering to men, particularly old men. “Maybe if you had an old grandpa, he was eating your food,” she speculates. Or it could be that because men can continue to reproduce, they are less vested in anyone other than their own children. Another possible reason is that women can be sure that a grandchild is their genetic descendant, but it is more difficult for grandfathers. This may also have spurred them to seek second and even third wives rather than focusing on their children. “We are comparing men who married once in their lifetime[s] with men who are married several times,” Lummaa says.


Two points. First, the idea that men are not sure about their offspring makes intuitive sense. Assume that there is 95% paternity within a pair-bond in relation to any given offspring. This means that if one is a paternal grandfather can be only 90% sure that one is the true grandfather (sons also have a 95% chance of paternity), and 95% sure if one is a maternal grandfather. The paternal vs. maternal distinction is important: data have shown that maternal grandmothers tend to be more beneficial than paternal ones. If mothers are a primary factor in survival the close relationship between the mother and her mother, as opposed to her mother-in-law (which in many cultures is stereotyped as antagonistic) makes intuitive sense. But, there is also the fact that paternal grandmothers in the situation I allude to above would only have 95% certainty about the paternity of her grandchildren.
But, there is another factor which comes to mind: perhaps old males contribute to group fitness (or, more properly, survival), but not familial fitness? My reasoning comes from the literature in cultural evolution which suggests that older individuals can be vessels for critical knowledge in environments due to their life experience. In many pre-modern societies where first order experience and analysis was likely to be faulty (consider whether you should consume a mushroom to confirm whether it is edible or poisonous) the few extremely aged members might have served is important consultative figures when rare events cropped up which might occur only once ever generation. In these cases both ancient males and females may have been important for group level survival. Because of customary division of labor males might also have information that women would have be privy to. Anyway, this is just a hypothesis which might explain why customs for keeping old men alive persist even if there is a negative affect on their own lineages’ fitness. Unfortunately it will be harder to confirm than simply looking at the reproductive values of individuals across a whole population.
Related: Group selection.

CATEGORIZED UNDER: Evolution
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This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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