The effects of kin propinquity on infant mortality.

Abstract This study tests the grandmother hypothesis and analyzes the effect of kin propinquity on infant mortality in a 19th century American frontier communal, polygynous population. The study shows that the presence of maternal grandmothers, aunts, uncles, and paternal aunts were significantly associated with increased infant survivorship while grandfathers, paternal grandmothers, and paternal uncles showed little effect. This study has implications for understanding the evolution of a long postreproductive life span, postmarital residential strategies, and behavioral strategies that enhance inclusive fitness.