VII.2.1 Gene flow may be the most important source of evolutionary novelties within a population.
While, within a metapopulation, evolutionary novelties arise primarily frommutation processes, gene flow is a much more likely within a population and is therefore more important source of novelties, such as mutated alleles. The incidence of migrants is usually much higher than the frequency of mutations in a population, with each migrant contributing his entire genome, i.e. a large number of alleles that may differ significantly from the alleles present in that population.
Gene flow and mutation processes as two sources of evolutionary novelties do not differ only in quantity. While an evolutionary novelty arising from mutation is harmful for its bearer in the absolute majority of cases, novelties acquired through migrants have already passed the natural selection test in another population and are therefore much more likely to be useful or at least selectively neutral.