Human migration has been studied from many points of view. In using a surname model to study its effects, however, one is concerned with migration from a single angle: as the mechanism that redistributes genes geographically. Human migration draws pedigree lines on maps. The pattern of such lines depicts an aspect of human population structure of signficance to population genetics: it is the obverse of inbreeding. Such mapping of pedigree lines can be used to help explain distributions of human genetic polymorphisms and even, perhaps, to predict future redistributions – or, more exactly, to describe the conditions that would lead to alternative outcomes. Human genes cannot move except by the movements of people who carry them. At least that was true before the invention of artificial insemination. Therefore, historically, human migration accounted for all the movement of genes.

Gene movement may be seen in the distances from birthplaces of parents to the birthplaces of their children. A certain amount of tracing of individual pedigrees has been done by geneticists and others. Such studies inevitably have a geographic aspect. Pedigrees, however, are not representative of the population as a whole: they are more likely to be complete with respect to higher social classes, successful and noteworthy individuals and patients with hereditary diseases. Male ancestors are usually easier to identify and trace than female ones, so the male line is usually more complete than female and mixed lines in pedigrees.