Migrants are in themselves worthy of study by human biologists because they encounter a number of health and behavioural problems as a consequence of moving into what are frequently very alien natural and social environments. The study of the migration process also enhances our understanding of the consequences of the spread of our species over the globe. For most human population biologists however, be they geneticists, anthropologists, epidemiologists or physiologists, the basic reason for an avid interest in migrants is the opportunity that they provide for understanding the underlying causes for variability in our species.

Although the rapidly expanding field of molecular genetics is developing exciting new explanations of the ways in which particular genes in suitable environments produce specific phenotypes, and previously unimaginable documentation of the past and present flow of genes through population movement, it seems unlikely that in the foreseeable future such studies will provide an explanation for most group and individual variability in human biology and behaviour. In the meantime migrant groups provide natural experiments which can be used to explain how genes and environment interact to produce both individual and group differences. Indeed it is only in the context of studying phenotypic development in contrasting and altered environmental conditions that we will be able to predict genetic effects on the phenotype. Within the discipline of human biology the study of migrants was initially used primarily to determine whether such traits as head shape and body size were genetically fixed traits in what were then termed races.