Modern Synthesis
Further information: Modern evolutionary synthesisThe modern evolutionary synthesis is based on the concept that populations of organisms have significant genetic variation caused by mutation and by the recombination of genes during sexual reproduction. It defines evolution as the change in allelic frequencies within a population caused by genetic drift, gene flow between sub populations, and natural selection. Natural selection is emphasized as the most important mechanism of evolution; large changes are the result of the gradual accumulation of small changes over long periods of time.
The modern evolutionary synthesis is the outcome of a merger of several different scientific fields to produce a more cohesive understanding of evolutionary theory. In the 1920s, R.A. Fisher, J.B.S. Haldane and Sewall Wright combined Darwin's theory of natural selection with statistical models of Mendelian genetics, founding the discipline of population genetics. In the 1930s and 1940s, efforts were made to merge population genetics, the observations of field naturalists on the distribution of species and sub species, and analysis of the fossil record into a unified explanatory model. The application of the principles of genetics to naturally occurring populations, by scientists such as Theodosius Dobzhansky and Ernst Mayr, advanced the understanding of the processes of evolution. Dobzhansky's 1937 work Genetics and the Origin of Species helped bridge the gap between genetics and field biology by presenting the mathematical work of the population geneticists in a form more useful to field biologists, and by showing that wild populations had much more genetic variability with geographically isolated subspecies and reservoirs of genetic diversity in recessive genes than the models of the early population geneticists had allowed for. Mayr, on the basis of an understanding of genes and direct observations of evolutionary processes from field research, introduced the biological species concept, which defined a species as a group of interbreeding or potentially interbreeding populations that are reproductively isolated from all other populations. Both Dobzhansky and Mayr emphasized the importance of subspecies reproductively isolated by geographical barriers in the emergence of new species. The paleontologist George Gaylord Simpson helped to incorporate paleontology with a statistical analysis of the fossil record that showed a pattern consistent with the branching and non-directional pathway of evolution of organisms predicted by the modern synthesis.
Read more about this topic: Introduction To Evolution
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