The phenotypic variance (VP) may be divided into the genetic variance (VG), the general environmental variance (VEg), and the special environmental variance (VEs). The latter is estimated through repeatability calculation (b). This value is considered the upper limit of heritability and represents maximum genetic variance proportion (VGm = VG + VEg) in relation to VP (b = (VG + VEg)/VP). This process allows an improved determination of biological relationships among groups from estimators maximizing the genetic information of quantitative characters. Two hundred and thirty-seven individuals inhabiting the northern coast of Chile for 4,000 years were taken as a sample. Measurement was made of six metric characters at both sides of the cranium. Special environmental values (es) were obtained by regression. The difference between these values and the phenotypic values (p) consists in the genetic values plus the general environmental values (g + eg). A mean b value of 0.83 indicated that VEs represents 17% of VP. The results showed: 1) high stability of the maximum genetic variance in time and space, 2) high correlation between the biological relationships model, the phenotypic model, and the maximum genetic model, and 3) random distribution of the nongenetic variation, as expected from the quantitative genetics theory. These results support the use of phenotypic data for the interpretation of the evolution history of prehistoric populations. Am J Phys Anthropol, 2006. © 2006 Wiley-Liss, Inc.