 The apparent incompatibility between Darwinian evolution and Mendelian inheritance persisted until 1918 when British biologist R.A. Fisher first indicated how the two sciences could be related; if traits were assumed to be the product of many Mendelian factors, then Darwinian natural selection could favor subtle variations in the traits, and the populations undergoing that selection pressure would gradually evolve all while the organisms in that population obeyed the Mendelian principles of inheritance (Fisher 1918). Fisher’s contribution was the first in a series of works—most notably by he, J.B.S. Haldane, and Sewall Wright—to reconceive of evolution as changes in population gene frequencies. The union of Mendel and Darwin came to be called “the modern synthesis”, and the mathematical models that Fisher, Haldane, and Wright developed launched the field of population genetics (Provine 1971; entry:  population genetics).  Evolutionary biology, which had long been made up of qualitative arguments about, for example, the similarity between selection on domesticated crops/livestock and selection in nature, suddenly became concerned with mathematical arguments about the quantifiable influences of migration, genetic drift, mutation, and natural selection on populations (entries:  ecological genetics;  heritability;  genetic drift).  