Reframing Interpretation of the Juvenility Index

Abstract

One of the most important ways that archaeology can contribute to the knowledge base for navigating contemporary concerns is by assessing the large-scale and long-term consequences of various social arrangements. The most straightforward and objective way of measuring these consequences is through their effects on demographic rates and population health. Paleo-demographers have converged on the Juvenility Index—the probability of dying between the ages of 5 and 20, given survival to age 5—as a relevant measure that can be estimated reliably and consistently from archaeological skeletal assemblages. However, interpretations of the index in the literature have been contradictory and lead to opposing conclusions concerning mortality, fertility, and population growth rates. In this paper, we propose a method for resolving this inconsistency. We treat the Juvenility Index as an age-specific mortality indicator, translate it into measures of life expectancy and the probability of survival to reproductive age through correspondences with model life tables, and then combine these with intrinsic population growth rates derived from settlement evidence to estimate fertility measures. We apply this method in a case study in the US Southwest, obtaining results that are consistent with other lines of evidence in suggesting that changes in the social arrangements of Ancestral Pueblo society did in fact lead to increased life expectancy, increased levels of human capital, and reduced childbearing burdens in the centuries prior to Spanish contact. Based on these results, further application of the method appears promising.