Do human parents face a quantity-quality tradeoff?: Evidence from a Shuar community

A number of evolutionary theories of human life history assume a quantity-quality tradeoff for offspring production: parents with fewer offspring can have higher biological fitness than those with more. Direct evidence for such a tradeoff, however, is mixed. We tested this assumption in a community of Ecuadorian Shuar hunter-horticulturalists, using child anthropometry as a proxy for fitness. We measured the impact of household consumer/producer (CP) ratio on height, weight, skinfold thicknesses, and arm and calf circumferences of 85 children and young adults. To control for possible phenotypic correlates that might mask the effect of CP ratio on anthropometry, we also measured household garden productivity, wealth, and social status. Regression models of the age-standardized variables indicated a significant negative impact of CP ratio on child growth and nutrition. The age-standardized height and weight of children in households with the largest CP ratio (10) were 1.38 and 1.44 standard deviations, respectively, below those of children in households with the smallest CP ratio (2). Surprisingly, garden productivity, wealth, and status had little to no effect on the fitness proxies. There was, however, an interesting and unexpected interaction between status and sex: for females, but not males, higher father status correlated significantly with higher values on the proxies.