Intra-individual variability and strontium isotope measurements: A methodological study using ⁸⁷Sr/⁸⁶Sr data from Pampa de los Gentiles, Chincha Valley, Peru

Measurement of ⁸⁷Sr/⁸⁶Sr relative abundance ratios in tooth enamel is a primary method to determine human paleomobility, and a growing number of studies now use these measurements to also reconstruct individual life histories and geographical origins. Here we test the utility and validity of this method for reconstructing individual life histories. To investigate intra-individual variability, we present results from blinded measurements of strontium isotope ratios in 42 tooth enamel samples from seven individuals found at the late prehistoric site of Pampa de los Gentiles, Chincha Valley, Peru. These samples include enamel that formed early in the development of the individual, as well as enamel that formed during adolescence. This allowed us to investigate normal variation in tooth enamel ⁸⁷Sr/⁸⁶Sr ratios. Within the same tooth type in the same individual, differences in ⁸⁷Sr/⁸⁶Sr ratios from right and left dental elements ranged from below the limit of detection (<0.00000, canine, Individual 23) to 0.00015 (first premolar, Individual 11). Because of the scale of this difference, these results validate the utility of intra-individual studies that focus on enamel that formed at different times during human development. The data also validate the utility of these strontium isotope ratio measurements when made to the third and fourth decimal place for making archaeological meaningful inferences about paleomobility.