Phenotypic variation of transitional forager-farmers in the Sonoran Desert

This study examines phenotypic variation and biological distances estimated using morphological traits from three Early Agricultural period (EAP) (2100 BC-AD 50) site-complexes in the Sonoran Desert of southern Arizona and northern Sonora. The hypothesis tested is that EAP forager-farmers were phenotypically homogenous as suggested by patterns in material culture and works to refine inferences regarding gene flow and biological affinity during subsistence transitions. Seven measurements from 62 EAP male and female crania were collected and used to calculate phenotypic variances, biological distances, and FST values with RMET 5.0 software. Analyses were applied to both pooled site-complex samples and to males and females separately. Results show differential variation between site-complex population samples, multiple significant biological distances, and significant FST values for the EAP regional sample that indicate widespread phenotypic heterogeneity rather than homogeneity. Significantly lower than expected variance in the Cienega Creek male sample is inferred to suggest a small closely related population present during the Cienega phase. Greater than expected male variation is attributed to higher frequencies of gene flow in the La Playa and Santa Cruz River site-complex samples. These EAP males are inferred to be more mobile across the Sonoran Desert landscape and representative of multiple biological affinities compared with females. This study provides evidence supporting the canalization of phenotypic variation when associated with human populations becoming increasingly sedentary due to transitioning subsistence practices.