The theories developed in the 1930s and 1940s to integrate molecular genetics with Darwinian evolution are called the modern evolutionary synthesis, a term introduced by Julian Huxley. Evolutionary biologists subsequently refined this concept, such as George C. Williams' gene-centric view of evolution. He proposed an evolutionary concept of the gene as a unit of natural selection with the definition: "that which segregates and recombines with appreciable frequency.":24 In this view, the molecular gene transcribes as a unit, and the evolutionary gene inherits as a unit. Related ideas emphasizing the centrality of genes in evolution were popularized by Richard Dawkins.