Temporal trends in craniometric estimates of admixture for a modern American sample

Temporal trends in craniometric estimates of admixture are investigated for three U.S. populations in the FDB. Patterns of association between birth years and posterior probabilities of cluster membership are identified to assess how these proportions of admixture have changed over recent time. Demographic and genetic data correlates, patterns of morphological expression, and shifts in source populations are evaluated.

Estimates of three-way admixture were obtained for 1,521 individuals of documented population, sex, and birth years that span the 20th century. Correlations were calculated between birth years and admixture proportions for members of each FDB population. Population and sex-specific admixture variation was further assessed by ANOVA and regression. Correlation analysis was used to identify, per population, which of the cranial measurements change in dimension under increased or decreased admixture.

Admixture proportions differ significantly by population and change over time. No sex differences are detected. Analysis of the relationship between admixture proportions and ILDs finds that admixture drives morphological change in areas of the cranium known to vary among populations. Results agree with prior work on secular change.

Findings reveal a progressive increase in White-European population admixture for the self-identified Black individuals, a recent demographic shift toward the increased representation of Hispanic individuals carrying greater Native American ancestry, and reduction in admixture for White individuals that suggest a loss of diversity over time. Changes in admixture produce tractable differences in morphological expression. Both sexes exhibit similar admixture proportions and self-identification patterns. Observed diachronic trends are corroborated by information on recent U.S. demographic change.