THE genetic structure of primitive human populations has been studied for the purposes of understanding hominid evolution and developing more cogent genetic models. For this it is important not only to demonstrate genetic variability between populations, but also to explore the correlates of such variability. Using data on several Chilean Indian populations I have found that genetic differentiation can best be ascribed to geographical separations. Other correlates, such as culture and language, are of secondary importance when the relationship is studied simultaneously by a stepwise regression technique 1. Although I consider here a particular set of populations, the results obtained seem to be fairly generally applicable2. I have found an empirical relationship between geographical distance and gene identity for the Andean highland Indians discussed here.