Balfour, Garstang and de Beer: The First Century of Evolutionary Embryology

Evolution has been integrated with embryology during two greatperiods: the latter half of the 19th C as evolutionary morphology/embryology,and the latter third of the 20th C as evolutionary developmentalbiology. My mandate was to use the contributions of three embryologists/morphologists:Francis (Frank) Balfour (1851–1882), Walter Garstang (1868–1949)and Gavin de Beer (1899–1972) to discuss the foundationsof evolutionary embryology in the UK from 1870 (when "everyaspiring zoologist was an embryologist, and the one topic ofprofessional conversation was evolution," Bateson, 1922, p.56), through the 1920s ("ontogeny does not recapitulate phylogeny,it creates it," Garstang, 1922, p. 81) to the 1970s ("homologyof phenotypes does not imply similarity in genotypes," de Beer,1971, p. 15). Evolutionary embryology was driven by a comparativeembryological approach that sought homology of adult structuresin germ layers and ancestry in embryos, and sought to differentiatelarval adaptations from retained ancestral characters. An initialemphasis on a phylogenetic mechanism (recapitulation) slowlygave way to more mechanistic approaches that included heterochronyand the integration of embryology with physiological genetics.Germ layers, homology, larval evolution, larval origins of thevertebrates, paedomorphosis and heterochrony underpinned theorigins of evolutionary embryology, and so I discuss each ofthese topics.