Population genetics is the study of the distribution of and change in allele frequencies under the influence of the four evolutionary forces: natural selection, genetic drift, mutation and migration. It also takes account of population subdivision and population structure in space. As such, it is the theory that attempts to explain such phenomena as adaptation and speciation.
Population genetics was a vital ingredient in the modern evolutionary synthesis, its primary founders were Sewall Wright, J. B. S. Haldane and Ronald Fisher, who also laid the foundations for the related discipline of quantitative genetics. Notable population geneticists of the mid-to-late 20th century include Japanese Mooto Kimura, American Richard Lewontin and Italian Luigi Luca Cavalli-Sforza.