In present day research in human biology, the validity of the concept of biological race rests on its utility as a research tool. The methodology of this research into human biological variability is a multidimensional application of the comparative method, utilizing, as one dimension, genetic distance. The body of this paper suggests two generalizing principles for the establishment of genetic distance. Genetic distance may occur due to physical or temporal isolation or in conjunction with environmental differences. A brief analysis of the fifteenth century human populations examines the relationship between these principles and presently used racial taxonomic systems. It is concluded that race may be defined operationally as a rough measure of genetic distance in human populations and as such may function as an informational construct in the multidisciplinary area of research in human biology.