DNA Reveals the Growing Ancestral Diversity of the United States

Demographic research often seeks to assess changes to the characteristics of a population over time. However, many sociodemographic variables, like race/ethnicity, are self-reported measuresthat correspond to a subjective sense of identity; this makes it challenging to distinguish [i] changes to fixed characteristics of a population from [ii] changing social norms and patterns ofself-identification. To address this issue, we utilize genetic similarity proportions (GSPs), which quantify the fraction of a person’s DNA linked to various present-day reference populations. Weanalyze the dynamic relationship between race/ethnicity and GSPs across three American birth cohorts: 1945, 1980, and 2015. Our results highlight the growing ancestral diversity of the U.S.over time, including both within-race/ethnicity shifts in average GSPs and changes to the association between GSPs and racial/ethnic identification.