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Conrad Hal Waddington
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Conrad Hal Waddington (1905-1975) was a British developmental biologist, paleontologist, geneticist, embryologist and philosopher. He was also known for his wide interests that included poetry and painting, as well as left-wing political leanings.
Waddington graduated from Cambridge University in 1927. From 1933 to 1945 he taught embryology at Cambridge, and in 1946 he became a professor of animal genetics at the University of Edinburgh. He was Fellow of the Royal Society of London from 1947. From 1961 to 1967 he was president of the International Union of Biological Sciences. Much of his work dealt with embryology, evolutionary genetics, and theoretical biology.
Waddington was influenced by the philosophy of Alfred North Whitehead.
He proposed that the "genetic assimilation" operated as a Darwinian mechanism that allows certain acquired characteristic to become heritable. According (Yong, 2009) "his theory suggests species initially cope with fresh environments by being flexible – through plasticity. All species have a certain amount of variation built in to their developmental program, which they can exploit according to the challenges they face. But as populations face constant evolutionary pressures, natural selection eventually favours genes that produce the same results, the ones that plasticity once achieved. This is the crux of Waddington’s theory – in time, natural selection eliminates plasticity by fixing genes for the same traits. Such genes as said to be “canalised”.
According to (Navis, 2007) "Waddington focused his genetic assimilation work on the crossveinless trait of Drosophila. This is a trait that occurs with high frequency in heat-treated flies. After a few generations, the trait can be found in the population, without the application of heat, based on hidden genetic variation that has been “assimilated.” His mechanism of "genetic assimilation" is sometimes cited as a Lamarckian mechanism however Waddington believed his mechanism could be reconciled into the neo-Darwinian synthesis.
Wallace Arthur wrote that "genetic assimilation, looks, but is not Lamarckian. It is a special case of the evolution of phenotypic plasticity." Waddington's theory of genetic assimilation is a rationalization of the “inheritance of acquired characters” within the context of natural selection and Mendelian genetics. He carried out experiments to support his theory in Drosophila by applying stress, in the form of heat shock to developing flies. According to (Mittelman and Wilson, 2010) Waddington had demonstrated that "morphological defects arise as a result of environmental stress and that the proportion of flies exhibiting these phenotypes increases under selection, and that continued selection for the novel traits results in their persistence, even in the absence of the original environmental stress."
Pigliucci et al, 2010 have written that Genetic assimilation (GA) is not a form of Lamarckism as the apparent "inheritance of an acquired character" which was explained by Waddington was described in standard Darwinian terms as selection on the activation threshold for the trait in question during development."
There has been a reignited interest in genetic assimilation as scientists have identified a molecular basis for Waddington's observations. A group of scientists have also discovered evidence for genetic assimilation in the heads of tiger snakes.
As part of his interest in theoretical questions of biology, Waddington joined the Theoretical Biology Club in the late 1930s.
Criticism of neo-Darwinism
Waddington is usually cited as a Darwinian and not a non-Darwinian. However some of the neo-Darwinian synthesis theorists described Waddington as a "non-Darwinian" as he claimed that different processes to those of microevolution drive macroevolution. According to (Wilkins, 2009) "[Waddington] in his lifetime... was widely perceived primarily as a critic of Neo-Darwinian evolutionary theory. His criticisms of Neo-Darwinian evolutionary theory were focused on what he saw as unrealistic, “atomistic” models of both gene selection and trait evolution. In particular, he felt that the Neo-Darwinians badly neglected the phenomenon of extensive gene interactions and that the “randomness” of mutational effects, posited in the theory, was a false postulate. Even though Waddington became critical of the neo-Darwinian synthetic theory of evolution, he still described himself as a Darwinian and his work attempted to correct and expand neo-Darwinism, not replace it.
Waddington's work on genetic assimilation has been revived and merged into the extended evolutionary synthesis. As (Pigliucci et al, 2010) writes "concepts such as GA and phenotypic accommodation, represent not a threat to the Modern Synthesis, but rather a welcome expansion of its current horizon."
- Waddington, CH (1940). Organisers & genes. Cambridge: Cambridge University Press.
- Waddington, CH (1941). The Scientific Attitude, Pelican Books
- Waddington, CH (1946). How animals develop. London: George Allen & Unwin Ltd..
- Waddington, CH (1956). Principles of Embryology. London: George Allen & Unwin.
- Waddington, CH (1957). The Strategy of the Genes. London: George Allen & Unwin.
- Waddington, CH (1959). Cellular and subcellular biological organization: proceedings of a symposium. London: Pergamon Press.
- Waddington, CH (1961). The human evolutionary system. In: Michael Banton (Ed.), Darwinism and the Study of Society. London: Tavistock.
- Waddington, CH (1966). Principles of development and differentiation. New York: Macmillan Company.
- Waddington, CH (1966). New patterns in genetics and development. New York: Columbia University Press.
- Waddington, CH, ed. (1968-72). Towards a Theoretical Biology. 4 vols. Edinburgh: Edinburgh University Press
- Induction and the Origins of Developmental Genetics by Scott F. Gilbert
- Diachronic Biology Meets Evo-Devo: C. H. Waddington's Approach to Evolutionary Developmental Biology by Scott F. Gilbert
- Biography of Conrad Hal Waddington
- Conrad Hal Waddington: the last Renaissance biologist? by Jonathan M. W. Slack Online at Link
- Article in Discover Magazine by Ed Yong October 30th, 2009
- Adam R. Navis, "Conrad Hal Waddington", Embryo Project Encyclopedia (2007) ISSN: 1940-5030.
- Science, Politics or Lamarckism? C. H. Waddington’s alternative approach to Darwinism by James F. Stark
- Wallace Arthur Evolution: A Developmental Approach 2011
- Stress, genomes, and evolution by David Mittelman and John H. Wilson
- Pigliucci et al, 2010 Phenotypic plasticity and evolution by genetic assimilation
- Hsp90 as a capacitor for morphological evolution. Rutherford SL, Lindquist S Nature. 1998 Nov 26; 396(6709):336-42.
- Big-headed tiger snakes support long-neglected theory of genetic assimilation
- From Epigenesis to Epigenetics The Case of C. H. Waddington by Linda Van Speybroeck
- Elizabeth Owen, Eve Daintith The Facts on File Dictionary of Evolutionary Biology 2009 p. 235
- Definition of Macroevolution at the Chemistry Encyclopedia
- Waddington’s Unfinished Critique of Neo-Darwinian Genetics: Then and Now by Adam S. Wilkins
- (Pigliucci et al, 2010) Phenotypic plasticity and evolution by genetic assimilation