Modern evolutionary synthesis
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The modern evolutionary synthesis (often referred to simply as the modern synthesis or the evolutionary synthesis), neo-Darwinian synthesis or neo-Darwinism, generally denotes the combination of Charles Darwin's theory of the evolution of species by natural selection, Gregor Mendel's theory of genetics as the basis for biological inheritance, and mathematical population genetics. Major figures in the development of the modern synthesis include Thomas Hunt Morgan, Ronald Fisher, Theodosius Dobzhansky, J.B.S. Haldane, Sewall Wright, William D. Hamilton, Cyril Darlington, Julian Huxley, Ernst Mayr, George Gaylord Simpson, and G. Ledyard Stebbins. Essentially, the modern synthesis (or neo-Darwinism) introduced the connection between two important discoveries; the units of evolution (genes) with the mechanism of evolution (selection). It also represents a unification of several branches of biology that previously had little in common, particularly genetics, cytology, systematics, botany, and paleontology.
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History
George John Romanes coined the term neo-Darwinism to refer to the theory of evolution preferred by Alfred Russel Wallace et al. Wallace rejected the Lamarckian idea of inheritance of acquired characteristics, something that Darwin, Huxley et al wouldn't rule out. The mechanism of inheritance wasn't discovered in Darwin or Wallace's time, however, so the debate was never settled.
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 differences.
A critical link between experimental biology and evolution, as well as between Mendelian genetics, natural selection, and the chromosome theory of inheritance, arose from T. H. Morgan's work with the fruit fly Drosophila melanogaster. In 1910, Morgan discovered a mutant fly with solid white eyes (wild-type Drosophila have red eyes), and found that this condition--though appearing only in males--was inherited precisely as a Mendelian recessive trait. In the subsequent years, he and his colleagues developed the Mendelian-Chromosome theory of inheritance and Morgan published The Mechanism of Mendelan Inheritance in 1915. By that time, most biologists accepted that genes situated linearly on chromosomes were the primary mechanism of inheritance, although how this could be compatible with natural selection and gradual evolution remained unclear.
This issue was partially resolved by Ronald Fisher, who in 1918 produced a paper entititled "The Correlation Between Relatives on the Supposition of Mendelian Inheritance", which showed using a model how continuous variation could be the result of the action of many discrete loci. This is sometimes regarded as the starting point of the synthesis.
Morgan's student Theodosius Dobzhansky was the first to apply Morgan's chromosome theory and the mathematics of population genetics to natural populations of organisms, in particular Drosophila pseudoobscura. His 1937 work Genetics and the Origin of Species is usually considered the first mature work of neo-Darwinism, and works by Ernst Mayr (systematics), G. G. Simpson (paleontology), G. Ledyard Stebbins (botany), C. D. Darlington (cytology) and Julian Huxley soon followed. Huxley coined both evolutionary synthesis and modern synthesis in his semi-popular work Evolution: The Modern Synthesis in 1942.
Tenets of the modern synthesis
According to the modern synthesis as established in 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, e.g. by geographic barriers.
Further advances
The modern evolutionary synthesis continued to be developed and refined after the initial establishment in the 1930s and 1940s. The most notable paradigm shift was the so-called Williams revolution, after George C. Williams presented a gene-centric view of evolution in the 1960s. The synthesis as it exists now has extended the scope of the Darwinian idea of natural selection, specifically to include subsequent scientific discoveries and concepts unknown to Darwin such as DNA and genetics that allow rigorous, in many cases mathematical, analyses of phenomena such as kin selection, altruism, and speciation.
A particular interpretation of neo-Darwinism most commonly associated with Richard Dawkins asserts that the gene is the only true unit of selection. Dawkins further extended the Darwinian idea to include non-biological systems exhibiting the same type of selective behavior of the 'fittest' such as memes in culture.
See also: Population genetics
References
- Dobzhansky, T. Genetics and the Origin of Species, Columbia University Press, 1937 ISBN 0-2310-5475-0
- Fisher, R. A. The Genetical Theory of Natural Selection, Clarendon Press, 1930 ISBN 0-1985-0440-3
- Haldane, J. B. S. The Causes of Evolution, Longman, Green and Co., 1932; Princeton University Press reprint, ISBN 0-6910-2442-1
- Huxley, J. S., ed. The New Systematics, Oxford University Press, 1940 ISBN 0-4030-1786-6
- Huxley, J. S. Evolution: The Modern Synthesis, Allen and Unwin, 1942 ISBN 0-0284-6800-7
- Mayr, E. Systematics and the Origin of Species, Columbia University Press, 1942; Harvard University Press reprint ISBN 0-6748-6250-3
- Simpson, G. G. Tempo and Mode in Evolution, Columbia University Press, 1944 ISBN 0-2310-5847-0
- Wright, S. 1931. "Evolution in Mendelian populations". Genetics 16: 97-159.
- Mayr, E. and W. B. Provine, eds. The Evolutionary Synthesis: Perspectives on the Unification of Biology, Harvard University Press, 1980 ISBN 0-674-27226-9
- Allen, Garland. Thomas Hunt Morgan: The Man and His Science, Princeton University Press, 1978 ISBN 0691082006
- Dawkins, Richard. The Blind Watchmaker, W.W. Norton and Company, Reissue Edition 1996 ISBN 0-393-31570-3
| Basic topics in evolutionary biology |
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| Processes of evolution: evidence - macroevolution - microevolution - speciation |
| Mechanisms: selection - genetic drift - gene flow - mutation |
| Modes: anagenesis - catagenesis - cladogenesis |
| History: History of evolutionary thought - Charles Darwin - The Origin of Species - modern evolutionary synthesis |
| Subfields: population genetics - ecological genetics - human evolution - molecular evolution - phylogenetics - systematics - evo-devo |
| List of evolutionary biology topics | Timeline of evolution | Timeline of human evolution |
