Helpful grandmothers in rural Ethiopia: A study of the effect of kin on child survival and growth

Kin selection and parental investment theories state that, in highly social species, such as humans, individuals can increase their inclusive fitness by extending support to their relatives. Here, we document patterns of kin support in a rural Ethiopian community, where postmarital residence practices provide differential access to relatives. Using demographic, anthropometric, and behavioral data collected from four villages we are able to (a) identify the effects of the presence of kin on child mortality and growth patterns and (b) provide detailed information on the role of relatives within the household.

Mortality analyses indicate that grandmothers had a positive effect on child survival. Anthropometric data reveal that maternal grandmothers had a particularly beneficial effect on child height, but paternal grandmothers less so. Time allocation data suggest that grandmothers continued to visit their daughters' households, irrespective of postmarital residence, where they relieved their daughters of heavy domestic tasks rather than helping with direct grandchild care. Matrilocal postmarital residence was associated with improved child survival, although children in matrilocal households were actually smaller. This may be due to wealth effects, increased competition between siblings, or higher survival of smaller infants in matrilocal households.     

Grandmaternal childcare and kinship laterality. Is rural Greece exceptional?

Grandmothers provide more childcare for their daughters' children than for those of their sons, almost everywhere. Exceptions occur where virilocal (patrilocal) postmarital residence makes the children of sons more accessible, but even under virilocality, preferential care of daughters' children, net of the effects of proximity, is often demonstrable. A unique counter-example has been reported by Pashos (2000, Evolution & Human Behavior, 21, 97–109) who found that rural Greek grandmothers cared more for their sons' children even when effects of proximity were controlled; however, this result was based on an analysis in which everything from living in the same household to living in nearby villages was treated as equally close.Here, we present new analyses that replicate Pashos's result, based on a large European survey with a finer differentiation of residential proximity. In interviews conducted in 2004–2007, rural, but not urban, Greek women indeed reported more care of sons' than of daughters' children, net of the effects of proximity and other variables, This rural reversal of the usual uterine (matrilateral) bias was not observed elsewhere in Europe. Greeks were not surveyed again until 2015, whereupon the pattern had disappeared, with rural women now exhibiting a strong uterine bias in grandchild childcare. It seems likely that the financial crisis of 2008–2009, which hit Greece especially hard, played some role in this dramatic change, but it cannot readily be traced to increases in either unemployment or multigenerational households.