Conrad Hal Waddington (1905–1975)


Conrad Hal Waddington (1905–1975) took a degree in Geology at Sidney Sussex College, Cambridge. He began but never finished a graduate degree; genetics and experimental embryology replaced palaeontology. He began experimental studies on the chemical nature of the primary organiser discovered by Spemann and Mangold in 1924. From collaboration with Joseph and Dorothy Needham and through the Theoretical Biology Club, came the concepts of evocation and individuation. Establishment of a Unit on Animal Breeding and Genetics in Edinburgh after the second World War provided Waddington with his professional home where he sought to integrate genetics and development into an evolutionarily relevant discipline. Adhering to the organic philosophy initiated by Alfred Whitehead (organicism) Waddington identified three major modes of explanation for the development of organisms as integrated wholes: canalisation, genetic assimilation and epigenetics. The metaphorical epigenetic landscape became the way most developmental biologists ‘saw’ the organisation of embryonic development. Integrated, heritable, epigenetic organisation of embryonic development is Waddington's lasting legacy to development and evolution.

Key Concepts

  • Canalisation is a homeostatic mechanism by which development is buffered against environmental or genetic variation, allowing the same feature to form under changing conditions.
  • Genetic assimilation is the process by which embryos respond to changes in the environment by producing a different phenotype, which, through selection, can arise in the absence of the environmental change.
  • Epigenetics (Waddingtonian epigenetics) is the term for the interactions among genes and between genes and environmental signals that result in the formation of elements of the phenotype.
  • Molecular epigenetics is the study of how mechanisms such as methylation or imprinting regulate gene action.
  • Interactions between parts of developing animal embryos (embryonic induction) are essential for the development of major body parts.

Keywords: canalisation; epigenetics; genetic assimilation; natural selection; environmental control; theoretical biology; experimental embryology; evolution

Figure 1. A wild‐type Drosophila (upper left) has a thoracic segment with wings and an abdominal segment with a rudimentary appendage known as a haltere. Bithorax Drosophila has two thoracic segments, both with wings and no abdominal segment, the second thoracic segment having formed where the abdominal segment normally would be. FlyBase. CC BY 2.0.
Figure 2. The epigenetic landscape as portrayed by Waddington . The ball at the top, representing an embryo or cell, proceeds through development down one canalised path or another. Environmental factors of genes (the walls of the valley) can redirect the embryo of cell into an alternate canalised pathway, resulting in alterations to the phenotype.
Figure 3. The Waddington Medal features, on the reverse face, a fossil ammonite as drawn by Waddington, and on the obverse, a chicken egg (lower), the wing of a Drosophila (upper) and pairs of chromosomes (left and right), encircled by an ouroboros (a snake swallowing its tale). The Greek adage from the philosopher Heraclitus (535–475 bc) can be translated as ‘all is one’. Courtesy of British Society for Developmental Biology.


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Further Reading

Ladewig J, Koch P and Brüstle O (2013) Leveling Waddington: the emergence of direct programming and the loss of cell fate hierarchies. Nature Reviews/Molecular Cell Biology 14: 225–236.

Lovino N and Cavalli G (2011) Rolling ES cells down the Waddington landscape with Oct4 and Sox2. Cell 145: 815–817.

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McCain KW (2009) Using tricitation to dissect the citation image: Conrad Hal Waddington and the rise of evolutionary developmental biology. Journal of the American Society for Informational Science and Technology 60 (7): 1301–1319.

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Peterson EL (2011) The excluded philosophy of Evo‐Devo? Revisiting. C. H. Waddington's failed attempts to embed Alfred North Whitehead's “Organicism” in evolutionary biology. History and Philosophy of the Life Sciences 33: 301–320.

Pigliucci M, Murren CJ and Schlichting CD (2008) Phenotypic plasticity and evolution by genetic assimilation. Journal of Experimental Biology 209: 2362–2367.

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Hall, Brian K(Mar 2020) Conrad Hal Waddington (1905–1975). In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0028954]