Modern evolutionary synthesis
The modern evolutionary synthesis (often referred to simply as the modern synthesis) brings together Charles Darwin's theory of the evolution of species by natural selection with Gregor Mendel's theory of genetics as the basis for biological inheritance. Major figures in the development of the modern synthesis include Ronald Fisher, Theodosius Dobzhansky, J.B.S. Haldane, Sewall Wright, Julian Huxley, Ernst Mayr, and George Gaylord Simpson.
Mendelian genetics was rediscovered in 1900. However, there were differences of opinion as to what was the variation that natural selection acted upon. The biometric school, led by Karl Pearson followed Darwin's idea that small differences were important for evolution. The Mendelian school, led by William Bateson, however thought that Mendel's work gave an evolutionary mechanism with large diffeences.
This issue was finally resolved by Ronald Fisher, who in 1918 produced a paper entititled On the correlation between relatives on the supposition of Mendelian inheritance, which showed using a model how discontinuous variation could be the result of the action of many loci. This is generally regarded as the starting point of the synthesis.
According to the modern synthesis as established in the decades of the 1930s and 1940s, genetic variation in populations arises by chance through mutation (this is now known to be due to mistakes in DNA replication) and recombination (crossing over of homologous chromosomes during meiosis). Evolution consists primarily of changes in the frequencies of alleles between one generation and another as a result of genetic drift, gene flow and natural selection. Speciation occurs gradually when populations are reproductively isolated by geographic barriers.
See also: Population genetics
History
Tenets of the modern synthesis
References