As a hallmark of our species, mothers of small children generally require and receive help from others in their reproductive efforts of parenting, in what can be called cooperative breeding. This help appears to affect the frequency of births and the success of reproductive efforts as measured by the health and survival of children. The nature of such effects in family systems organized around women and in which women control resources holds interest with respect to the evolution of the human species. The matrilineal Khasi tribe of N. E. India are swidden agriculturalists characterized by low socioeconomic resources and high natural fertility (average is 6.7 children). Women are economically active in the fields, markets, and in home ownership. Khasi households, which may have several married or single women and men are organized around the matriline, often consisting of three generations. A woman is free to choose her own husband who may or may not join the household. Our data represent 773 households providing lineage and reproductive histories comprising 3,274 births. Dependent variables include interbirth interval, cumulative net reproductive success by age of mother, and child nutritional status and mortality (172 deaths). Within this strongly matrilineal context, we examine measures of reproductive success in terms of local resource enhancement and resource competition models with respect to sibling and older offspring effects (depending on sex, age and birth order). We also examine the effect of husband’s presence and of grandmother’s help at the birth of a child, and her continued presence in the household.


Social and Behavioral Sciences



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