Fig. 5

⁸⁷Sr/⁸⁶Sr human values from the Upper Atbara graveyards (UA50 and UA53), plotted by chronology, sex, and age class. The yellow dashed lines indicate the local Sr range (as 0.70682–0.70701), defined through Tukey’s interquartile range calculated solely on subadults’ values. (5) Of the 18 total individuals, 9 fall outside the local range.