The Combined Effects of Selection and Migration in Human Evolution

Regional continuity in Australasian Pleistocene hominid evolution

“…We contend that the dynamic model of longlasting morphological clines that results from a balance between geneflow and opposing selection (Hiorns and Harrison, 1977), best accounts for the observed pattern. Indeed, the "center and edge" hypothesis provides a solution for one of the problems discussed by these authors by suggesting how marked genetic differences might be established over a continuous range before the leveling effect of geneflow resulted in their dispersion.…”

“…Indeed, the "center and edge" hypothesis provides a solution for one of the problems discussed by these authors by suggesting how marked genetic differences might be established over a continuous range before the leveling effect of geneflow resulted in their dispersion. Hiorns and Harrison (1977) show that numerous combinations of geneflow and opposing selection at low magnitudes can lead to a clind equilibrium over a series of adjacent populations when the selection is uniform. In a more realistic approximation, varying magnitudes of selection would widen the range of combinations of these two forces over which such an equilibrium can be established.…”

Genetic assimilation in ethnic minorities

“…The existence of gradients, or clines, of gene frequencies between spatially separate populations can be substantiated by differences in measured amounts of selection, selection coefficients, in the different environments. However, when migration is enlisted to explain clines, the assumptions which need to be made concerning differential selection may be grossly simplified (Hiorns & Harrison, 1978). When such simpler assumptions are made, migration can even be adduced as necessary to the maintenance of these clines over time.…”