Poulton, Edward Bagnall
POULTON, EDWARD BAGNALL
(b. Reading, England, 27 January 1856; d. Oxford, England, 20 November 1943)
natural history, entomology, evolutionary biology.
Poulton was the second of three children and only son of a successful architect, William Ford Poulton. His mother, Georgina Selina Bagnall Poulton, was author of an 800-page history of England. Poulton carried the family regard for professionalism, hard work, and close attention to voluminous detail throughout his career. The family was comfortable enough for him to be educated at a succession of boarding schools, primarily W. M. Watson’s new school at Oakley House, Reading. Poulton entered Oxford in 1873 and remained there for the rest of his career, which included an honors degree in zoology (1876), various demonstratorships, a geology research scholarship, lectureships, and finally election to the Hope professorship of zoology in 1893, from which he retired in 1933. He received the D.Sc. in 1900.
A large and robust man not prone to hiding his enthusiasms, Poulton entered vigorously into the life of the university, both in his department and museum and in the wider field of university affairs. He was extremely active, and regularly held office, in the British Association for the Advancement of Science (president, 1937), the Linnean Society of London (president, 1912–1916), and especially the Entomological Society of London (president, 1903–1904 and 1925–1926), which named him honorary life president in 1933, when it became the Royal Entomological Society. He had a wide circle of colleagues, correspondents, and friends. Poulton married Emily Palmer in 1881; they had two sons and three daughters, of whom Poulton survived all but one. Of his many honors, knighthood in 1935 was the most public recognition of a long career.
That career had its inauspicious, if rather traditional, beginnings in natural history. From early childhood, Poulton was an insect collector and observer. His fledgling interests in natural science did not suit the schools’ orientation to the classics, and little of his schooling was scientific. It was not unusual for Poulton to find himself defending entomological pursuits against the derision of even his masters, who questioned their utility. Having gained his scientific education from his own reading, he attempted but failed to obtain a scholarship to Oxford, and began work in his father’s office in 1872.
At the time it was typical in Britain to gain a natural history education by independent study, although professorships in the biological sciences had been established at Oxford and Cambridge in the 1860’s. Continued late-night study convinced Poulton’s father of his serious scientific intentions, and he then was encouraged to work and study part-time at the University Museum, Oxford. The choice of Oxford was largely because of his mother’s wish that he attend that university, but it proved to be a most fitting choice for a budding naturalist primed to receive the influence of some of the best of the Victorian zoologists.
In 1873 Poulton attended the lectures of George Rolleston, first Linacre professor of anatomy and physiology, and worked in his department at the University Museum three days a week. The result was success in the examinations for a Jesus College science scholarship, enabling him to attend university. He also spent the last hours of the day in the Hope department of entomology, examining specimens and talking with John Obadiah Westwood, first Hope professor and foremost entomologist in Britain, if not the world. Never converted to Darwinism, Westwood attempted to warn the young, enthusiastic entomologist against it, but the lesson had little impact; Poulton read Darwin’s Origin of Species and was convinced by it. Westwood continued to help, nonetheless, even if his taxonomic orientation did not suit Poulton’s far more ecological interests in entomology. More directly inspiring as a teacher was Rolleston, who captured Poulton’s imagination and inspired him to pursue a career in zoology.
Westwood and Rolleston were typical of Oxford biologists in their emphases on taxonomy and comparative morphology, rather than on the newer experimental physiology. Under Rolleston’s influence, Poulton progressed from amateur natural history to comparative morphology, with its distinctively Darwinian questions about development and phylogenetic evolution. He chose to stay at Oxford after graduating, to work under Rolleston. But as inspiring as Rolleston was, he was not skilled at directing research. Nor did Poulton find much time, after his duties as demonstrator, for original work.
Frustrated, and in a precarious financial situation, he studied for and won the Burdett-Coutts scholarship in geology in 1878, which enabled him to work with Joseph Prestwich, the professor of geology. He enthusiastically began research under his new mentor, and thus his first scientific publications were on geological topics. Not surprisingly, given his wish to return eventually to zoology, the stra-tigraphic results in his analysis of a Reading riverbed included detailed discussion of mammalian remains.
The opportunity to work in zoology came with the appointment of Henry N. Moseley as Linacre professor in 1881. Poulton, by then a Keble College tutor, had started a series of microscopic studies on mammalian tongues and taste organs. Moseley learned of these and immediately encouraged Poulton, aiding him by providing study material from the Challenger expedition. With a little prompting. Poulton’s research flourished into a series of papers in the 1880’s on the comparative anatomy and evolutionary origins of taste buds and other structures of the duck-billed platypus.
His researches on monotremes and marsupials had important Darwinian implications. Poulton presented a transitional sequence for these mammals, to show how complex adaptive structures of the tongue could be built gradually by the specialization of ordinary epithelial parts. He revealed in detail the origins, in a primitive group, of distinctive, higher features. The duck-billed platypus, classified as the nearest living representative of the ancestral form through which mammals evolved, seemed an evolutionary enigma as a transitional form because it lacked the teeth so characteristic of mammals. Poulton solved the problem by examining a series of young specimens and showing that the animal possesses true teeth that are lost before adulthood. Poulton’s analysis of the structure and embryology of the platypus’ hair led him to argue that mammalian hair is a persistence from reptilian ancestors. He used the independent persistence, loss, or development of important class features among reptiles, early mammals, and later mammals to deduce the linkages and transitions essential to the construction of phylogenies.
Well set on a course of research widely acknowledged to be the foremost task facing evolutionary morphologists, and with aid from people established in the field, Poulton at the same time began a series of rather different investigations in entomology. The taxonomical work typical of museum entomologists did not appeal to him, but Alfred Russel Wallace’s Contributions to the Theory of Natural Selection (1870) had in 1878 aroused an interest in working on insects, especially the phenomena of coloration. As Poulton’s morphological research got under way, Raphael Meldola’s translation of August Weiss-mann’s Studies in the Theory of Descent (1880–1882) appeared, and it directly inspired Poulton to a new kind of Darwinian research in 1883. Meldola’s editorial comments were provocative suggestions for research; Poulton, starting with the question of how the cryptic green color of certain caterpillars is acquired, quickly made his morphological studies experimental and physiological, in a novel combination of field and laboratory work. Meldola promoted the work, as did Weismann, Moseley, Wallace, and E. Ray Lankester.
Thus Poulton again was elevated into the ranks of the foremost Darwinian zoologists of the day, culminating with his election to the Royal Society in 1889. Although he had been trained in classical natural history, including its taxonomical and geological emphasis, Poulton’s experimental methods were nevertheless relatively novel, just as his questions about the ecological aspects of insect biology had been little investigated. The combined inspiration from the naturalist Wallace and the experimental morphologist Weismann, the leading spokesmen for Darwinism, led Poulton to the lifelong course for which he would become most famous—his ardent defense of Darwinian natural selection as the mechanism of evolution.
Poulton’s transformation of research methodology in studying the colors of insects mirrors the changes in natural history research in the late 1800’s. From a taxonomic and morphological base, he first investigated, from 1884 through the 1890’s, such questions as how green coloration is acquired from plant chlorophyll and the causes of other correlations of insect color with the colors in the environment. Next, in 1886, he began experiments on the relations of insect colors to the selection pressures faced by the insect. Experimental demonstration of the effectiveness of cryptic colors as protection against predators was a welcome addition to the Darwinian argument, especially since Poulton’s extensive, detailed experiments were innovative amid the typically observational data of natural history.
But the methods of comparative morphology did not completely disappear; Poulton created a comparable argument with comparative ecology to support Darwinism. Poulton’s version of ecology, growing out of the tradition of such Darwinian naturalists as Wallace and Henry Walter Bates, continued to stress comparative studies as it concentrated on the organism’s adaptations to its environment. Interest in the ecology of adaptation was, for Poulton, tied to the provision of new, more rigorous arguments for natural selection. Indeed, the study of adaptations had become the special province of the most vocal Darwinians, even as the mechanism of natural selection was declining in popularity among physiologists, embryologists, and students of heredity.
The adaptation that had particularly captured Poulton’s interest was the phenomenon of protective colors and resemblances, presented in Wallace’s influential essay of 1867, which was reprinted in Contributions to the Theory of Natural Selection. Wallace had elaborated upon Bates’s discovery of mimicry, in which one butterfly species mimics, or resembles in superficial coloration, an unrelated species, called the model. Bates had argued in 1861 that the models were protected from predators such as birds by various qualities, such as bad flavor or tough bodies: the mimics had evolved a disguise to cover their own defenselessness by taking on the color patterns of the models. Protective resemblance would be favored in the struggle for existence, in what seemed to be a proof in nature for the theory of evolution by natural selection.
Wallace made explicit the theoretical connection of this mimetic form of resemblance to other, well-known instances of protective coloration, such as camouflaged insects that look like sticks or leaves. Poulton’s interest in cryptically green caterpillars started with their significance for the selectionist argument: and Weismann had in fact been arguing against competing, physiological theories that tried to eliminate the need for natural selection in the explanation of such phenomena as coloration.
This was not the only Weismann campaign to which Poulton devoted his research: he also used his insect morphology studies to attack neo-La-marckian theories of the inheritance of acquired characteristics. Poulton also took on the task of getting Weismann’s Essays upon Heredity and Kindred Biological Problems translated into English and published in 1889. Support for Weismann’s germ-plasm theory as the mechanism of heredity consistent with the operation of natural selection was the theme Poulton carried on a lecture tour of America in 1894. As Darwinism was being eclipsed in the 1890’s by newer evolutionary theories, Poulton joined Wallace and Weismann in leading the defense of natural selection as the predominant mechanism of evolution.
Poulton’s first major foray into the battle was The Colours of Animals (1890), in which he extended the arguments from Bates and Wallace. Starting with a brief survey of the way in which colors are physically produced, he argued that the explanation of why an organism has its particular colors lies in the utility or significance of those colors for its survival. The entire book, devoted almost exclusively to insects—indeed, to butterflies—was one long argument that coloration demonstrates natural selection in action in nature. Drawing together a large number of studies, and emphasizing experimental results when possible, Poulton surveyed the known cases of protective resemblances, sexual dimorphisms, mimicries, and other useful coloration. By relating them to their uses in defense or otherwise, he reorganized the various phenomena of appearance into a scheme based on adaptiveness. In so doing, he introduced terminological rigor by separating and naming the varieties of defensive colors, crypticity, mimicry, warning colors, alluring colors, recognition marks, and courtship displays.
Much of Poulton’s presentation merely gave details of adaptation, to convince the reader of the validity of Darwinism. In fact, his major explicitly theoretical argument was directed within the selectionist camp. He supported Darwin on sexual selection, against Wallace’s view of the opposition of natural selection to sexual selection. He rejected Wallace’s theory that male colors are due to a surplus of physiological vitality. Poulton briefly countered a handful of other proposed mechanisms for acquisition of coloration that explained it by internal mechanisms without regard for external selective pressures.
This would become the theme for Poulton’s Darwinian arguments for the next forty years: internal mechanisms explain little of the evolutionary acquisition of adaptations, which must find their explanation in the external relations of the organism with its environment. The dichotomy between internal and external causes was the framework for his arguments against the unfolding of embryological plans, recapitulation of phylogeny, physiological orthogenesis of various coloration patterns, and the sufficiency of merely physical causes of colors in explaining their significance. He was one of the first Darwinians to make the strong distinction between these proximate causes and the ultimate evolutionary causation. Poulton’s internalist-externalist dichotomy was also the framework in which he received the new Mendelian genetics after 1900, seeing it as one more inadequate analysis of the causation of adaptive form.
In many ways, The Colours of Animals was the prelude to Poulton’s greatest body of work. It was with this survey of protective resemblances that he began research on mimicry. It was a widely noticed entry into the increasingly polemical debate over Darwinism, presenting his perennial denial of the inheritance of acquired characters and support for natural selection as the only sufficient explanation for the evolution of adaptation. In both arguments he depended more and more after 1890 on evidence from mimicry.
Poulton’s enormous body of work on mimicry truly got under way, however, only with his appointment to the Hope professorship upon West-wood’s death in 1893. The chair was recognized as Britain’s leading entomological position, and Poulton was entrusted with the University Museum’s large collection of insects. He took the opportunity to transform the Hope Collection, turning from the traditional taxonomical orientation to a more ecological one. He specialized in mimetic species, gathering specimens over broad geographical ranges and emphasizing the variation in nature. This was a radical change in museum method and purpose, and Poulton fully intended this new working collection to be a resource for the proof of natural selection. It also meant that over the forty years of his tenure he expanded the collection enormously, frequently using his own money as well as incessantly petitioning the university for more funding. He built a worldwide network of corresponding naturalists and collectors; more than one of these correspondents came to work in unofficial positions in the department. Encouragement of a number of entomologists and extremely active involvement in the Entomological Society of London gave Poulton great influence. He was a major figure in orienting the field toward ecological and evolutionary studies.
Mimicry was the vehicle of this change. Facing the attacks of non-Darwinian evolutionary theorists, Poulton devoted himself to developing the Bates-Wallace claim that mimicry is the natural experiment proving the operation of natural selection. The grand Darwinian argument that he thought was overlooked in the proposed internalist mechanisms of evolution was the biogeographical evidence. Species collected widely enough show a distribution of variation, and these small or continuous variations, he argued, are the stuff of evolution. Since only natural selection of useful variations could explain acquisition of adaptive structure, it was necessary to investigate the bionomics, or ecology, of the species involved. In his new position, Poulton continued the experiments on relations of insect color to environment, as well as a new series in 1898 and 1899 to measure the predation dangers facing insects. Most of his detailed ecological data, however, came from his growing network of naturalists, especially in Africa.
From 1897 through the 1930’s, Poulton published regularly on mimetic complexes of Africa, creating the paradigmatic case study of mimicry with the Papilio swallowtail butterflies and their associated species. He and his collaborators (including, at various times, Roland Trimen, Guy A. K. Marshall, W. A. Lamborn, C. A. Wiggins, Harry Eltringham, and G. D. Hale Carpenter) unraveled the often confusing and mistaken taxonomy and ecology of the several butterfly species involved in this mimicry ring. They argued that sexual dimorphism within the group revealed ancestral and derived forms, with geographical distributions providing consistent evidence. The males remained close to the ancestral condition while the females diverged into the wide range of mimetic color and form. They collected the apparent transitional forms from the predicted sites and, more important, were able to breed and rear butterflies with characters supporting their general argument for the gradual acquisition of the adaptive coloration.
Guy A. K. Marshall, of South Africa, was Poul-ton’s most important collaborator in gathering field evidence that bird predatton is a great and documentable selective pressure on butterflies. The lack of quantitative or experimental evidence was a frequent criticism of scenarios of natural selection. From observations made between 1897 and 1902, Poulton orchestrated a campaign in the pages of the Transactions of the Entomological Society of London to demonstrate the action of this selection in nature. Such attempts proved to be convincing only in the short run, since the same criticism, doubting the importance of predation, appeared in 1915 from the geneticist Reginald C. Punnett and again in 1932 from the ecologist Waldo L. McAtee. Each time Poulton used the pages of the Transactions to solicit support from naturalists in the field and to present his own voluminously detailed collection of evidence.
Although continued, the geographical and ecological data collection begun in the 1890’s was augmented after 1903 with breeding experiments. In part, Poulton needed the results of crosses of different geographic races or mimetic forms to reveal the possible evolutionary pathways of transitional forms within a mimetic complex. More critically, however, after 1900 the rediscovery of Mendelism and its assimilation into antiselectionist, mutationist theory impelled Poulton to respond to the new genetics. From 1901 through the early 1920’s, a dominant motif within Poulton’s argument for natural selection was a reaction to the mutationist interpretation of hereditary variation. It was a heated debate in general, and Poulton responded to the strong claims of William Bateson with sharply worded papers and addresses. He gathered and edited his most substantial papers on theories of heredity, evolution, and mimicry into Essays on Evolution; 1889–1907 (1908). In a polemical preface on mutationism and Mendelism, he complained about the claims of de Vries and Bateson that they had explained evolution with mutations and without any need for natural selection. For Poulton it was yet another example of the internalist error in explaining an externalist cause. Moreover, he resented the belittling of the contributions of the great naturalists.
The book was Poulton’s most influential single work, capping the raging debate during the 1909 Darwin centennial, cogently arguing the case for natural selection, and presenting in one place many examples within his argument for mimicry as the proof for selection. He also included a 1904 address in which he redefined species, in an early statement of the modern biological species concept, in order to stress continuous variation and belittle notions of speciation by single mutation. Poulton was a highly visible spokesman for Darwinism during the Darwin centennial, writing a paper on mimicry in the Cambridge celebratory volume Darwin and Modern Science (1909) and writing the historical and theoretical Charles Darwin and the Origin of Species (1909), a sequel of sorts to his earlier Charles Darwin and the Theory of Natural Selection (1901). In all of these forums, he argued for the role of the naturalist able to see natural selection in action in ecological studies. The data on variation, gathered widely in the field, were to be taken as seriously as the laboratory Mendelism.
The heat of the polemic undoubtedly obscured Poulton’s compromise position on genetics. Opposed to the Mendelian embracing of discontinuous variations as the raw material of evolution, he tried to demonstrate how coloration phenomena developed from continuous variation. The complexity of the adaptations also was an argument for their gradual building. Miscast as opposed to Mendelism, he actually argued that it only clarified Weismann’s germ-plasm theory, and that small variations would be seen to be Mendelian. It was another decade before biologists began to accept that continuous variation is indeed Mendelian; and most geneticists were convinced from laboratory work, not from Poulton’s breeding or field data from mimetic species.
For a few important contributors to the Modern Synthesis, combining the evolutionary theory of Darwinism with Mendelism, however, Poulton did have a great influence. Mimicry again was the vehicle. Through a debate with Punnett over the genetic basis of mimetic color and its evolution, Poulton attracted and collaborated with G. D. Hale Carpenter, his eventual successor in the Hope chair, and Ronald A. Fisher, a principal architect of the synthesis.
Punnett began a running debate with Poulton over the Mendelian mutationist version of mimicry, in a series of articles (1913–1914) in the pages of Bedrock, a short-lived journal for scientific controversy that Poulton helped to found and edit. In Mimicry in Butterflies (1915), Punnett recapitulated his arguments for the single large-step creation of mimetic resemblance. He also doubted the standard ecological scenario of bird predation and the geographical relationships of mimic and model, drawing on both field studies and breeding results for a swallowtail butterfly complex of southeast Asia. Poulton could belittle Punnett’s knowledge of taxonomy, ecology of butterflies, and awareness of the wealth of other data, but he could not deny the genetic results that implied discontinuous mutational steps in the evolution of the mimicry.
Poulton’s response was to depend more on the other cases he had built, especially the African swallowtails, for which he had breeding results supporting continuous steps of variation. Carpenter’s work in Africa, directed largely by Poulton through correspondence, gave the critical biogeographical data. Poulton took it and emphasized the complexity of the complete Darwinian story, with its genetical, morphological, taxonomical, geographical, and ecological consistency. But he also attacked the mutationists on their own theoretical ground. In papers of 1914 and 1916, he called for a new definition of mutation that would reduce its size and thus make continuous variation part of the same Mendelian mechanism as Punnett’s larger steps, which Poulton took to be rare and usually useless. The papers were little noticed, partly because of the war and partly because of Poulton’s typical style of burying the theoretical suggestions within a mass of entomological detail.
Fisher noticed the same argument that Poulton was making in William E. Castle’s results on modifier genes and the genetical nature of continuous variation, and began his series of theoretical papers in 1918. In 1927 he had Poulton’s help with the mimetic examples and data to produce an influential paper on modifier genes and the Darwinian basis of mimicry, providing a new model to explain Punnett’s case. As a chapter in Fisher’s Genetical Theory of Natural Selection (1930), the mimicry case developed by Poulton and Fisher exerted great theoretical influence. Fisher’s frequent collaborator Edmung B. Ford, who had been Poulton’s student at Oxford in the 1920’s elaborated, from 1933 to 1980, the ecological genetics of mimicry as the paradigmatic proof of adaptation by natural selection. He and Carpenter collaborated on Mimicry (1933), which briefly summed up much of the data and argument developed at the Hope department. By this time, Poulton had done much to solidify mimicry’s place as a demonstration of natural selection.
Poulton, however, never produced the anticipated masterwork on mimicry, although he gathered plates and manuscript for it for years. The deaths of three of his children between 1915 and 1919, especially the loss of his younger son in World War I, slowed him considerably. By his retirement in 1933, despite colleagues’ hopes for a summary work, Poulton was in his seventies. He had never been able to disengage himself from the mass of details in running the department and collections, supervising and assisting his correspondent naturalists. Perhaps most important, he hewed closely to the incredible intricacies of his research material, as often as not obscuring the impact of his theoretical discussions. For instance, his 1880’s papers on insect colors contained early, yet unnoticed, versions of a concept of frequency-dependent selection, so important in the later work of Ford and others.
Poulton’s tenure as Hope professor both created and constrained his work, ultimately leaving much of his work to be carried out by colleagues, protégés, and the institution he largely created. He spent his career promoting ecological studies over traditional taxonomy, in the process helping to carry ecology into university specialization in Britain. He was instrumental in aiding his protégé Marshall in the establishment of the Imperial Bureau of Entomology, an early governmental applied science institution. Foremost among these indirect influences were his constant defense of the Darwinian theory and the creation of a body of scientists developing its details.
I. Original Works. Poulton’s best-known works are The Colours of Animals (London, 1890), and Essays on Evolution (Oxford, 1908), which includes many of his most important papers. A useful guide to 137 of his more than 200 publications is the scholarly bibliography, arranged by subject, in G. D. Hale Carpenter, “Edward Bagnall Poulton,” in Obituary Notices of Fellows of the Royal Society of London, 4 (1942–1944), 655–680. Poulton included an autobiographical chapter in his memoir John Viriamu Jones and Other Oxford Memories (London, 1911). His papers and correspondence are in the Hope Entomological Library, University Museum, Oxford.
II. Secondary Literature. G. D. Hale Carpenter wrote several obituaries of Poulton; the most complete biographical treatment is his notice for the Royal Society of London (see above). On Poulton’s views on mimicry and the genetical debates leading to the Modern Synthesis, see William C. Kimler, “Mimicry: Views of Naturalists and Ecologists Before the Modern Synthesis,” and John R. G. Turner, “‘The Hypothesis That Explains Mimetic Resemblance Explains Evolution’: The Gradualist-Saltationist Schism,” both in Marjorie Grene, ed., Dimensions of Darwinism (Cambridge, 1983). On Poulton’s role in twentieth-century ecology, see William C. Kimler, “Advantage, Adaptiveness, and Evolutionary Ecology,” in Journal of the History of Biology, 19 (1986), 215–233. For a detailed treatment of Poulton’s mimicry research and debates, see William C. Kimler, “One Hundred Years of Mimicry: History of an Evolutionary Exemplar” (Ph.D. diss., Cornell University, 1983).
William C. Kimler
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