Neo-Darwinism, the modern version of Charles Darwin's theory of evolution by natural selection, incorporates the laws of Mendelian genetics and emphasizes the role of natural selection as the main force of evolutionary change. The term neo-Darwinism was first used in the 1880s by August Weismann, a German naturalist, who incorporated his theory of the germ plasm into Darwin's theory of evolution by natural selection. Weismann advocated the theory that the body is divided into germ cells, which can transmit hereditary information, and somatic cells, which cannot. Weismann thereby added a mechanism of heredity different from Jean Baptiste de Lamarck's inheritance of acquired characteristics, which prepared the ground for the rediscovery of Gregor Mendel's laws of inheritance by Erich von Tschermak, Hugo deVries, Carl Correns, and William Bateson around 1900.
The rediscovery of Mendel's work led first to a critique of Darwin's theory of evolution, as the new school of Mendelians (Bateson, deVries, and others) believed that differences in discrete traits among individuals were too big to fit into Darwin's theory of gradual change of phenotypes. Another school of thought that developed during the first two decades of the twentieth century involved the biometricians (Karl Pearson, Francis Galton, and others), who opposed the view of the Mendelians and studied small differences in so-called quantitative traits (e.g., body size), using statistical methods and assuming that most genes had only minor effects on traits. The controversy between Mendelians and biometricians was resolved by R. A. Fisher in 1918 when he showed that Mendelian inheritance and gradual changes in phenotypes were not incompatible. In the following two decades Fisher, J. S. B. Haldane, and Sewall Wright used mathematical tools to elaborate on this combination of the laws of genetics and Darwin's theory of evolution, thereby developing the modern synthesis and the new field of population genetics.
Modern synthesis, which has since been called the "neo-Darwinian theory of evolution," was soon accepted and integrated into different biological disciplines, including population genetics, comparative anatomy, zoology, biogeography, palaeontology, and systematics. Influential books, such as Genetics and the Origin of Species (1937) by Russian-born American experimental biologist Theodosius Dobzhansky, The Modern Synthesis (1942) by British biologist Julian S. Huxley, Systematics and the Origin of Species (1942) by German-born American zoologist Ernst Mayr, and Tempo and Mode of Evolution (1944) by American palaeontologist George Gaylord Simpson are examples of this development and of the neo-Darwinian theory of evolution as having become broadly accepted among contemporary biologists.
Evolution from a neo-Darwinian viewpoint is defined as genetic change in populations through time (descent with change), with modern organisms being descendents of earlier, different organisms. In addition to natural selection, mutation, random genetic drift (i.e., random fluctuations in gene frequencies due to chance), and gene flow are considered important factors of evolutionary change with mutation being the ultimate source of genetic variation.
See also Darwin, Charles; Evolution; Genetics; Lamarckism; Mendel, Gregor
dobzhansky, theodosius. genetics and the origin of species. new york: columbia university press, 1937.
huxley, julian s. evolution: the modern synthesis. london: g. allen and unwin, 1942.
mayr, ernst. systematics and the origin of species. new york: columbia university press, 1942.
simpson, george gaylor. tempo and mode of evolution. new york: columbia university press, 1944.