Gene flow

Gene flow is the migration of alleles from one population to another. The migration of alleles, especially the immigration of individuals carrying new alleles, can have significant effects on the allele frequency of a population. It is consequently one of the key driving forces of evolution, along with natural selection and genetic drift.

Consistent gene flow between populations can lead to reduced genetic diversity in those populations as the individuals' genotypes become homogenised. This acts against speciation since individual gene pools are not left isolated for long enough to become reproductively separate from their neighbouring populations. Gene flow is easier when the individuals concerned are practically able to move between populations - for example, when there is no geographic or manmade barrier to their migration.

From a conservationist point of view, gene flow can be damaging as it leads to a phenomenon called genetic pollution, whereby a wild species is threatened by an uncontrolled and undesirable influx of alleles from other, perhaps more 'fit', organisms who dominate and 'pollute' the naturally existing gene pool.