Conrad Hal Waddington

{{Evolution}}
'''Conrad Hal Waddington''' {{lived|1905|1975}} was a [[United Kingdom|British]] developmental [[biologist]], paleontologist, [[geneticist]], embryologist and [[philosopher]]. He was also known for his wide range of interests, including poetry and painting, as well as his [[left-wing]] political leanings. He was influenced by the philosophy of Alfred North Whitehead. 

==Biography==

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 elected a Fellow of the Royal Society of London in 1947 and served as president of the International Union of Biological Sciences from 1961 to 1967. Much of his work dealt with embryology, evolutionary genetics and theoretical biology.<ref>[http://encyclopedia2.thefreedictionary.com/Conrad+Waddington Biography of Conrad Hal Waddington]</ref>

==Evolution==

Waddington was a leading embryologist and geneticist from the 1930s to the 1950s and is remembered mainly for his concepts of the {{wpl|Epigenetic Landscape|Epigenetic Landscape}} and {{wpl|Genetic Assimilation|Genetic Assimilation}} (GA).<ref>[http://www.nature.com/nrg/journal/v3/n11/abs/nrg933.html Conrad Hal Waddington: the last Renaissance biologist? by Jonathan M. W. Slack] Online at [http://wwworm.biology.uh.edu/evodevo/lecture3/slack02.pdf Link]</ref>

He proposed that the "genetic assimilation" operated as a Darwinian mechanism that allows certain acquired characteristic to become [[heritable]]. According to a 2009 article in ''Discover Magazine'', "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”.<ref>Article in Discover Magazine by Ed Yong October 30th, 2009 </ref> 

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.”<ref>Adam R. Navis, "Conrad Hal Waddington", Embryo Project Encyclopedia (2007) ISSN: 1940-5030.</ref> His mechanism of "genetic assimilation" is sometimes cited as a [[Lamarckism|Lamarckian]] mechanism however Waddington believed his mechanism could be reconciled into the [[neo-Darwinian synthesis]].<ref>[http://www.academia.edu/1658254/Science_Politics_or_Lamarckism_C._H._Waddingtons_alternative_approach_to_Darwinism Science, Politics or Lamarckism? C. H. Waddington’s alternative approach to Darwinism by James F. Stark]</ref> 

{{wpl|Wallace Arthur|Wallace Arthur}} wrote that "genetic assimilation, looks, but is not Lamarckian. It is a special case of the evolution of phenotypic plasticity."<ref>Wallace Arthur ''Evolution: A Developmental Approach'' 2011</ref> 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."<ref>[http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3006615/ Stress, genomes, and evolution by David Mittelman and John H. Wilson]</ref>

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."<ref> Pigliucci et al, 2010 [http://jeb.biologists.org/content/209/12/2362.full Phenotypic plasticity and evolution by genetic assimilation]</ref>

There has been a reignited interest in genetic assimilation as scientists have identified a molecular basis for Waddington's observations.<ref>Hsp90 as a capacitor for morphological evolution. Rutherford SL, Lindquist S Nature. 1998 Nov 26; 396(6709):336-42.</ref> A group of scientists have also discovered evidence for genetic assimilation in the heads of tiger snakes.<ref>[http://blogs.discovermagazine.com/notrocketscience/2009/10/30/big-headed-tiger-snakes-support-long-neglected-theory-of-genetic-assimilation/ Big-headed tiger snakes support long-neglected theory of genetic assimilation]</ref>

Waddington was also the inventor of the term {{wpl|epigenetics||.}}<ref>[http://www.uv.mx/evargas/CienciaSagrada/TextosFundamentales/Speybroeck.pdf From Epigenesis to Epigenetics The Case of C. H. Waddington by Linda Van Speybroeck]</ref>

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]].<ref>Elizabeth Owen, Eve Daintith ''The Facts on File Dictionary of Evolutionary Biology'' 2009 p. 235</ref> 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]].<ref>[http://www.chemistrydaily.com/chemistry/Macroevolution Definition of Macroevolution at the Chemistry Encyclopedia]</ref> 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.<ref>[http://www.mitpressjournals.org/doi/pdf/10.1162/biot.2008.3.3.224 Waddington’s Unfinished Critique of Neo-Darwinian Genetics: Then and Now by Adam S. Wilkins]</ref> 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. 

===Extended synthesis===

Waddington's work on {{wpl|genetic assimilation|genetic assimilation}} has been revived and merged into the [[extended evolutionary synthesis]]. As ([[Massimo Pigliucci|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."<ref>(Pigliucci et al, 2010) Phenotypic plasticity and evolution by genetic assimilation</ref>

==Quote mining==

Waddington is sometimes [[quote mined]] by [[creationist]]s as being anti-Darwinian and a critic of [[natural selection]]. However, these claims are false; Waddington did not deny natural selection.

==Works published==

*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 

==External links==
*[http://9e.devbio.com/article.php?ch=2&id=27 Induction and the Origins of Developmental Genetics by Scott F. Gilbert]
*[http://icb.oxfordjournals.org/content/40/5/729.full Diachronic Biology Meets Evo-Devo: C. H. Waddington's Approach to Evolutionary Developmental Biology by Scott F. Gilbert]

==References==
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[[Category:Biologists]]
[[Category:British people]]
[[Category:Paleontologists]]
[[Category:Philosophers]]

Categories: Biologists, British people, Paleontologists, Philosophers