in “Grandma plays favourites: X-chromosome relatedness and sex-specific childhood mortality” (posted about previously here), fox, et. al., showed that “the grandmother effect” (greater survival of grandkids due to the presence of a grandmother) differs between paternal and maternal grandmothers and whether we’re talking about grandsons or granddaughters. this is due to differing degrees of relatedness between the different types of grandmothers and grandkids:
the authors predicted — and did, indeed, find — that the presence of paternal grandmothers (pgm) should be most beneficial to granddaughters; maternal grandmothers (mgm) should be equally beneficial to grandsons and granddaughters; and the paternal grandmother (pgm) – grandson relationship should be the least beneficial:
interestingly, they found quite a wide variance in how beneficial (or not) each of the grandmas was (click on image for LARGER view):
my question is: is this variance in, for instance, how beneficial the presence of a pgm is to a granddaughter connected in any way to a population’s mating patterns? pgms, on average, are more related to their granddaughters (their sons’ daughters) in a society which practices mother’s brother’s daughter (mbd) marriage than in a society which practices father’s brother’s daughter’s (fbd) marriage — and both much more than in a society which doesn’t practice any inbreeding:
the numbers for granddaughter suvivorship in the presence of a pgm were relatively low for (a) germany, (b) england, and (d) canada as compared to, say, (e) japan where i know there was cousin marriage historically and that it was likely mbd marriage, the most common form of cousin-marriage in the world and quite common in east asia.
what about the other societies? what sort of marriage/mating patterns do/did they have? do mating patterns affect the grandmother effect? inquiring minds want to know!
previously: all grandmas are not created equal
(note: comments do not require an email. nuthin’ like grandmas!)