Asymmetric Caregiving by Grandparents, Aunts, and Uncles and the Theories of Kin Selection and Paternity Certainty: How Does Evolution Explain Human Behavior Toward Close Relatives?

Abstract

Evolutionary theories explain altruism between related individuals, not only for nonhuman animals but also humans themselves. In sociobiology and evolutionary psychology, the supposedly universally found stronger matrilineal kin caregiving by grandparents, aunts, and uncles is often explained by paternity uncertainty in the male descent line. The present article provides an overview of theories and results of the evolutionary research. I will focus, in particular, on the universal caregiving pattern as well as on cultural variety in kin caregiving, the role of actual paternity certainty in the society, theoretical inconsistencies, and nonconsanguineous step relationships. From the analysis of the empirical data, I will conclude that the paternity certainty hypothesis is in fact not a very suitable explanation for the asymmetric kin caregiving found in humans. I will discuss how human behavior toward relatives, in particular grandchildren, can be alternatively explained from an evolutionary perspective.

A model explaining the matrilateral bias in alloparental investment

“…The other example is one in which rural residents in Greece reported having received more care as children from PGMs than from MGMs, whereas urban residents reported the reverse (40). Pashos (40,41) maintains that these rural Greek PGMs provided more childcare than MGMs, even when the two lived "equally far away," which, if true, would constitute a unique demonstration of preferential investment in AGCs. However, the distance measure for this analysis was too crude to warrant such a strong conclusion: residence in the same household, "in the same town," or in a "neighboring village" were all scored as equally, maximally, close at hand, leaving the question of a preferential caregiving net of differences in accessibility unresolved.…”

Offspring fertility and grandchild survival enhanced by maternal grandmothers in a pre-industrial human society

“…The population parameter of paternity uncertainty is an ancestral, taxonwide parameter, but the impact this might have had on patrilineal grandmaternal behaviour is unknown and may be negligible. Furthermore, paternity uncertainty as an explanation often ignores societal differences 10,63 , is not universally supported 64,65 , and cannot be explicitly tested in historical societies without genotyping. Differential X-chromosome inheritance (i.e.…”

Do mothers also “manipulate” grandparental care?

“…Although there might certainly exist cultural effects on decision making among all parents, our “manipulative mother hypothesis” (i.e., that mothers mentally exploit the alloparenting environment by expressing biased resemblance descriptions) could explain many of the results not entirely predicted by the “paternity uncertainty hypothesis” alone (see Pashos, 2017 ). For example, the higher grandparental investments observed among maternal grandfathers compared to that of the equally uncertain paternal grandmothers ( Euler & Weitzel, 1996 ), the larger caregiving toward nieces and nephews observed among maternal aunts compared to that of paternal aunts ( Pashos & McBurney, 2008 ) and the maintenance of a high matrilateral caregiving among orthodox Jews under high paternity certainty ( McBurney et al, 2002 ) are all results that correspond to a larger manipulation of the alloparenting environment among mothers than fathers.…”