Abstract
A major transition in human population structure is currently under way, moving from a historical metapopulation, comprising small and mainly rural endogamous communities, to large and increasingly panmictic urban populations. This process is predicted to increase outbreeding, and preliminary data from genomic surveys have helped to quantify the potential magnitude of the effects. Population genetic trends of this nature should result in a reduced burden of recessive disorders, and have a favourable impact on complex diseases influenced by partially recessive genetic variants of smaller effect. The overall outcome is expected to be beneficial for a range of traits associated with human health and disease that show dominance variance.