Maternal grandparents go the extra mile?

Family Ties That Bind: Maternal Grandparents Are More Involved In The Lives Of Their Grandchildren:

For grandparents living within 19.5 miles (30 km) of their grandchildren, over 30% of the maternal grandmothers had contact daily or a few times a week. Around 25% of the maternal grandfathers had contact daily or a few times a week. In contrast, only around 15 % of the paternal grandmothers and little more than 15% of the paternal grandfathers would have contact daily or a few times a week.

The sample was Dutch, and the authors hypothesize that the reason that maternal, as opposed to paternal, grandparents go the extra mile is that they are wholly certain of their genetic relationship. In other words, motherhood is certain and fatherhood is theoretical (though this varies by society). This isn't a new finding, and the results can be found in societies. It also manifests in the Grandmother Effect studies, maternal grandmothers quite often invest more than paternal grandmothers in their grandchildren.

What I am interested in is the fact that this finding is counterintuitive when you take into account the cultural ideals and traditions promoted by most cultures. That is, the majority of the world's societies are patrilineal and patrifocal, and yet even in these societies this tendency is manifest. Reading about Indo-European philology I was struck that some scholars point out that these languages tend to have special terms for the maternal uncle, and yet the conventional stereotype is that the Indo-Europeans were catalysts for the transition toward a patriarchal and patrilineal society (I think this is somewhat exaggerated, as the more female friendly nature of pre-Indo-European cultures is often based on conjecture in lieu of hard data, but the reality remains that most Indo-European societies were male-focused). And yet even within extremely patriarchal societies the role of maternal relatives remains prominent, even surprisingly so.

A few years back I read a study of the Khasi of northeast India, who were matrilineal and exhibit an admirable degree of sexual equity in a South Asian context, and Bangladeshi villagers in the lowlands to their south who reflect the more conventional male-dominated dynamic. When examining the investment of grandmothers both the Bengali and Khasis showed a maternal bias! This surprised me, and yet it also did not. In my own family (which is Bengali) the same pattern exists, an inordinate and socially embarrassing closeness with maternal relatives (uncles and grandparents) combined with the nominal fact that the lineage is conceived of purely in a patrilineal manner. In my own family the juxtaposition was acknowledged in a humorous fashion and my mother would note that it wasn't proper, but the dynamic has persisted across all these years. I had assumed that we were anomalous, but now I am not sure sure. The same tension between cultural norms and biosocial realities seem evident in the negative Grandfather Effect noted in Finland, that is, the presence of these older men who are likely the living representations of their lineages reduces the fitness of their descendants!

I suspect you have several countervailing dynamics going on here. On the one hand there might be an increase in individual fitness for practice x, but a decrease in group fitness if said practice increases in frequency, and the inverse. As societies become more "advanced" there seems to be a trend toward a transition toward greater patriarchy until modernity, as such, kicks in. Consider the transition from the ubiquity of queens in early Japan to the obligate descent of the Imperial throne through males later on. Or the transition across South India from matrilineal practices toward patrilineal oens. In a between-cultural competition in seems that with the rise of mass societies, but before the rise of the consumer one, a strongly patrilineal and patriarchal cultural state is favored. But this is relatively recent in our evolutionary background, and it may be that on the individual level there has been quite a bit of breach of these forms and customs. It seems to me the same tension between our instinctive impulses and cultural expectations exists in societies which practice obligate arranged marriage; there still tends to be embarrassments due to the yearnings of young people which are contrary to the interests of their families. And the ballads and legends of these societies, where arranged marriage is obligate and the ideal, are suffused with tales of romantic love. In the adaptive acceleration paper there was a reference to the fact that culture can drive directional evolution. That's the simple case. I don't think that the implications some of the baroque customs & traditions of the mass societies that arose after agriculture as as easy (I suspect in many societies there was a class element to the adherence of particular customs).