Edward Bagnall Poulton's life and work spanned a period of immense historical and scientific change. The Crimean War was coming to an end as Poulton was born on January 27, 1856. Charles Robert Darwin's On the Origin of Species lay only three years in the future. Attending Oxford beginning in 1873, he studied under anatomist George Rolleston and eminent entomologist (and anti-Darwinian) John Obadiah Westwood. Three years later Poulton had earned an honors degree in zoology. During the closing years of the nineteenth century, Poulton lived through the zenith of British imperialism and the nadir for acceptance of natural selection as an evolutionary mechanism. Among biologists, little consensus existed on the role of natural selection. A few neo-Darwinians, led by August Weismann, accepted natural selection yet rejected most other mechanisms. Others, as did Darwin in later editions of the Origin, supplemented natural selection with other mechanisms. Many more, such as the American neo-Lamarckians, rejected natural selection outright in favor of inheritance of acquired characters and internal, directed mechanisms. Members of all these groups argued about whether evolutionary change was gradual or saltational. From the 1880s onward, although biologists agreed that organic evolution had taken place, they continued to argue about how and why.

After Westwood's death, Poulton in 1893 became the Hope professor of zoology. During his long tenure at Oxford, Poulton witnessed the rediscovery Mendelian genetics, the increased professionalization and specialization of biological sciences, the rise of population genetics and many significant changes in the biological sciences. The importance of experimental evidence as opposed to description continued to grow from the 1890s onward. The majority agreed upon evolution as such, yet argued over the appropriate methods for studying it. Poulton took part in the heated debates between paleontologists, field naturalists, geneticists and others. As Hitler was coming to power in Germany, Poulton retired from Oxford University. Having lived through the terrible destruction of the Great War, Poulton's final publication came in 1938, on the eve of the Second World War. As WWII raged, he died on November 20, 1943. Only a year prior, Julian Huxley had published his statement of the modern evolutionary synthesis. Between the Crimean and Second World War, the world had witnessed many violent changes. Similarly, between Darwin's Origin of Species (1859) and Huxley's Evolution: the Modern Synthesis (1942), evolutionary thought had seen tremendous changes. All of this had taken place during Poulton's lifetime.

With over 200 publications spanning nearly sixty years, Poulton's work (including five books, numerous addresses, articles, essays and letters) covers a wide range of topics from insect bionomics to biography, mimicry to morphology, geology to geographical distribution. Such an extended corpus provides an excellent opportunity for examining continuity and change in his thought. Many questions come to mind. How did Poulton react to the "eclipse of Darwinism" (i.e., rejection of natural selection) of the 1890s? How did his ideas change with the rise of Mendelian genetics? How did he react to the evolutionary synthesis? In short, how did Poulton’s ideas develop from the early 1880s through the late 1930s? How did he respond to the wider shifts in biological thought? Addressing these questions is the primary goal of this paper. Despite all the changes, it will become apparent that Poulton's work contained a high degree of continuity.

Poulton was, at heart, an entomologist. His work reflects a long-lasting interest in the study of insects. From nearly 140 works listed by entomologist George H. Carpenter, almost 70% deal directly with entomology. At the age of eighty-two Poulton reflected:

Poulton rejected Darwin's pangenesis in favor of Weismann's continuity of germ-plasm. Pangenesis stated that gemmules from every part of the body traveled to the sex cells during reproduction. These countless gemmules carried specific information about each part of the body and passed on parental characteristics to the offspring. Pangenesis, therefore, allowed for the inheritance of acquired characters. Poulton rejected pangenesis because of its "well-nigh insuperable" difficulties and its "almost infinite complexity." In addition, mutilations or blood transfusions, according to pangenesis, should pass characters to the offspring, yet there was no evidence from experiments by Weismann and Francis Galton that this ever occurred. Weismann's theory, on the other hand, divided heredity into somatogenic (i.e., acquired) and blastogenic (i.e., inherited) characters. Only blastogenic characters could be passed on in the germ-plasm (i.e., the sex cells). Poulton noted

If mutilations, results of training, exercise or education, or certain diseases could be shown to be inherited, then Weismann's theory would "inevitably collapse." Such direct evidences, however, failed to stand the test of thorough investigation. Not one convincing demonstration of the inheritance of acquired characteristics existed. Even so, Poulton did not totally omit the possibility of Lamarckian mechanisms. Phenomena such as individual variation, instinctual habits and use/disuse were not well understood. If any of these could be shown impossible without the transmission of acquired characters, then Poulton admitted that Weismann's theory would fail. Until shown otherwise, he would reject Lamarckism.

Colours of Animals adhered to his plan by amassing examples of coloration. The surface colors of higher animals had developed such that "their amount, their arrangement in patterns, their varying tints, and their relation to the different parts of the body, have all been determined by natural selection through innumerable generations." Animal coloration reduced to the following classes:

1) Colors of Direct Physiological Value (e.g., dark colors absorb radiant heat)

2) Protective and Aggressive Resemblance (i.e., camouflaging of prey or predator)

3) Protective and Aggressive Mimicry (i.e., superficial resemblance of another animal to gain advantage)

4) Warning Colors (i.e., bright colored patterns advertising unpleasant attributes such as taste or smell)

5) Colors displayed in Courtship (i.e., colors modified by preference due to aesthetic sense in highest animals).

As Poulton's examples piled up, his message came across quite clearly. Natural selection (for classes 2-4) and sexual selection (for class 5) provided the best and most comprehensive explanation for an otherwise bewildering and inexplicable variety of phenomena. The strongest evidence, perhaps, came from the study of mimetic resemblance. Poulton, who published many papers on the subject, considered mimicry one of the most important aspects of animal coloration.

Early in the nineteenth century, resemblances between distant species had been recognized. For example, an entomology text from 1818 commented that insect imitation afforded "a beautiful instance of the wisdom of Providence." In another case "the Author of nature" had provided the likeness. Natural theology using the argument from design was the guiding principle explaining these mimetic likenesses. In 1861, after many years in the jungles of Brazil, English naturalist Henry Walter Bates proposed a new explanation. Bates claimed that certain palatable species of butterflies resembled other species which were conspicuously-patterned and unpalatable. The predators, usually birds, learned to recognize and avoid the warning pattern of the unpalatable model via experimental tasting. The mimic gained protective advantage because predators associated its similar warning pattern with an unpalatable model. How had the mimic come to resemble the model? Bates’s answer was natural selection. Charles Darwin and naturalists such as A. R. Wallace enthusiastically embraced Batesian mimicry as evidence of natural selection in action. Bates’s theory was quickly extended to other parts of the world in studies by Wallace (1866) and Roland Trimen (1870). Poulton made explicit the selective process in Colours of Animals:

The many known instances of mimicry, concluded Poulton, "strongly confirm[ed] the view that these resemblances [were] produced by the operation of natural selection." He also reiterated the conditions or "laws" of mimicry as given by A. R. Wallace:

1) Mimics inhabit the same area as model.

2) Mimics are always more defenseless than the model.

3) Mimics are always less numerous than the model.

4) Mimics differ from most of their allies.

5) Mimicry is external and visible only, not extending to internal characters.

Although naturalists like Darwin, Wallace, Trimen and Poulton accepted Batesian mimicry, many others questioned or rejected selectionist explanations. An immediate problem was Wallace's laws.

Poulton, overstating the widespread acceptance of natural selection, attacked Beddard’s work. According to him, Beddard rejected natural selection for reasons "which will strike the instructed and uninstructed reader alike as singularly inadequate." Despite Poulton's review, Beddard was not alone in his wariness to accept natural selection or in his suggestion of external forces as the cause of mimicry.

Charles Coe’s Nature versus Natural Selection (1895) took an even stronger anti-selectionist position. This book of nearly 600 pages was devoted entirely to arguments against natural selection. Coe's position was clear:

He criticized many, including Poulton, for accepting natural selection as an unquestioned law. For some, selection had become dogma rather than science. For Coe, as for Beddard, external forces were the cause. Species with similar climate, diet and living conditions were "transformed into the same outward resemblance by the same external conditions." External forces, not natural selection, were the key cause.

American paleontologist Edward Drinker Cope also doubted the efficacy of natural selection. Cope mentioned Wallace, Poulton and Beddard in his 1896 book, The Primary Factors of Organic Evolution. The first two authors, he noted, assigned natural selection as the cause of protective resemblances. Natural selection, however, could not cause variations in color. Cope, like Beddard, Coe and others, favored external physico-chemical forces such as moisture, cold or lighting as the cause. Cope also pointed out Poulton’s experiments on lepidopterous larvae as evidence of the direct action of the influences of light on animal pigment.

In 1892, Poulton had compiled the results of several years of research. Like many others, he attempted to determine the effects of colored surroundings, lights and varied diets upon numerous species of Lepidoptera during different stages in their development. Poulton found that many larvae took on the colors of their surroundings (e.g., become darker when black twigs were mixed with their food, than when surrounded by green leaves and twigs). Furthermore, his experiments illustrated that color change only took place during specific developmental stages, operated within a limited color range and were not passed on to the offspring. Cope saw Poulton’s experiments as clear evidence of the action of external forces. As a neo-Lamarckian he remained unconvinced that such changes were not heritable. Poulton, on the other hand, agreed that the changes were in the direction of concealment, yet noted:

He concluded that this "marvellous power of individual adaptation to environment had been acquired through the ordinary processes of natural selection." The battle between natural selection and alternative mechanisms continued.

In the closing years of the century, Poulton reiterated the triumphs of natural selection and the deficiencies of Lamarckianism through his addresses, historical essays and mimicry studies. During this period and into the twentieth century, Poulton met much opposition to his views.

Darwin, clearly the hero of evolutionary theory, remained an inspiration for Poulton's continuing work on butterfly mimicry. With the emergence of Hugo DeVries's mutation theory and the rediscovery of Mendelian genetics, debates about the evolution of mimicry slowly took a different direction.

In March 1898, Poulton read a paper at the Linnean Society on mimetic resemblance and common warning colors. Batesian mimicry, he claimed, was stronger now and more widely held among students of other animal groups than among entomologists. During meetings of the Entomological Society of London the previous summer, Poulton discovered that many doubted selectionist mimicry. Of those entomologists he asked, only three excluding himself fully supported Batesian and Müllerian mimicry. The others doubted the inedibility/unpalatability of the models (some investigators even performed taste tests!) or were not convinced that birds had been proven effective selective agents. The theories of Bates and Müller required more experiment and observation. External and internal forces remained popular alternatives to natural selection.

Poulton, seemingly in the minority, constantly appealed to the broad explanatory powers of natural selection. Only under selection, he wrote, did the various resemblances of animals "fall together into a natural arrangement and receive a common explanation." Alternative theories were narrower in explanatory power or simply did not work. The theory of external influences, for instance, required the transmission of acquired characters, yet there was no evidence for this hypothesis. Other theories simply did not explain the vast amount of facts which natural selection made intelligible. This, said Poulton, "increases our confidence in the theories of Bates and Müller, while it disposes of all alternative hypotheses." Mimicry, in fact, was "one of the most notable triumphs ever won by the great theory of natural selection."

With his neo-Darwinian stance, Poulton continued meeting resistance. In 1899 botanist George Henslow took exception to his views. He concluded that selection was not a physical cause, therefore, its powers were imaginary. In a mocking tone, Henslow remarked that natural selection seemed:

In his opinion, external conditions coupled with "inward adaptive powers of protoplasm" and "habits of life" caused mimetic resemblance. Henslow and numerous others relied on external and internal forces as the vera causa of evolutionary change. Henslow concluded that selection had "no raison d'être in the origin of any structure whatever."

Despite Poulton's claims that natural selection had been widely accepted, it is evident from Henslow's statements and that Lamarckian explanations had not disappeared. Poulton's repeated defenses indicate that many opponents still existed. His address to the Fifth International Zoological Congress in 1901 clearly illustrates this point. This speech evaluated specific instances of mimicry according to the rival theories, i.e., natural selection, external forces and internal forces. In cases where certain species mimicked features of distantly-related aggressive species, Poulton systematically ruled out alternative theories. He concluded:

Many biologists in the late nineteenth and early twentieth centuries questioned a mimicry theory which relied on natural selection and the accumulation of minute variations. Questions arose including: How could minute variations confer advantage and accumulate? Was there convincing evidence of bird predation to indicate selection pressure? Could tiny variations persist and alter an entire population? How were tiny individual variations passed from generation to generation? These and other questions remained problems not just for mimicry, but for natural selection in general. Some investigators including neo-Lamarckians, Mendelians and even selectionists saw part of the solution in saltational explanations. For example, American biologists David Starr Jordan and Vernon Kellogg believed in natural selection, yet wondered why small initial variations would confer advantage to the mimic. It seemed implausible that a tiny spot of color on a butterfly’s wing would make a bird mistake it for another species. They argued that the leap must be saltational rather than gradual. Poulton, on the other hand, insisted that gradual accumulation of minute variations, through natural selection, was the key.

By the 1890s, Cambridge biologist William Bateson had latched on to the discontinuous mutation theory of Dutch botanist Hugo DeVries. De Vries, breeding evening primroses, discovered that these flowers suddenly changed or mutated from one generation to the next. With the rediscovery of Mendel’s work (c 1900) by Bateson, DeVries and others, the discrete character of Mendelian factors held special interest for investigations which focused on discontinuity. Geneticists turned to saltational or mutational explanations for mimicry and evolutionary change in general. In 1908, Poulton described his disagreements with Bateson. He was extremely dismayed by Bateson’s unfounded attacks on Darwin and natural selection. Mutationism and Mendelism, he explained, had been injurious to biological science for the following reasons:

Consistent with his earlier work, Poulton remained a defender of the work of Darwin, Wallace and Weismann. By de-emphasizing the importance of natural selection, Bateson and the "ill-informed" had obviously erred. Mutations still needed the action of natural selection to be of any consequence; otherwise, mutation theory, said Poulton, merely revived special creation under another name. Referring to Bateson he wrote, "error is a not unnatural outcome of the depreciatory and contemptuous tone adopted by the leader of Mendelism in this country." When it came to the relative importance of Mendelian and Darwinian ideas, Poulton and Bateson were poles apart. For Poulton, although Mendelian research deserved the "warmest appreciation," it was of negligible importance compared to natural selection. Bateson accepted natural selection, but regarded it as self-evident and not very interesting. Of real importance were Mendelian genetics.

Yet again, Poulton explicitly rejected mutational jumps when it came to mimicry. He wrote:

Between 1910 and 1915, Reginald Crundall Punnett fully elaborated a Mendelian explanation of butterfly mimicry. In 1910, his paper on polymorphic mimetic butterflies of Ceylon (e.g., Papilio polytes) explained the many barriers to accepting natural selection as the formative cause of mimicry. According to Punnett, the selective value of minute variations and their inheritance still lacked experimental proofs. The absence of transitional forms and the frequent lack of mimicry in male butterflies were also troubling for selectionist theory. Finally, was the enigma of polymorphic mimicry. Some species of butterfly mimicked not merely one, but several models. In breeding experiments these polymorphs cleanly segregated according to Mendel’s law of segregation. For Punnett, none these observations were explained by gradual selectionism. Instead the evidence suggested that mimicry had arisen from sudden mutational jumps. Once a mimic was formed by mutation, natural selection played only a conservative role. Selection was not the formative cause of mimicry. "Unknown conditions," noted Punnett, had brought about similar mutations in widely disparate species of butterflies which already contained similar sets of pattern factors. He compared this to similar mutant coat colors such as chocolate or agouti which appeared in both guinea pigs and rabbits.

Between 1912 and 1914, Poulton and Punnett debated mimicry in a series of articles which appeared in a short-lived journal for scientific controversy called Bedrock. Poulton repeated the unreasonableness of supposing all mimetic features arose simultaneously in one saltation. For a particular butterfly he said:

Poulton concluded that "the hypothesis that explains mimetic resemblance explains evolution." This clearly indicates his continued devotion to natural selection and its intimate connections with mimicry.

Although both Poulton and Punnett accepted Mendelism and natural selection, they assigned distinct roles to each. They had quite different understandings of these concepts. Confirmed by breeding experiments, Poulton was perfectly willing to accept Mendelian ideas such as dominant and recessive factors. However, as reflected in the title of his next paper, "Mimicry, Mutation and Mendelism," Poulton downplayed the importance of Mendelism. Mimicry formed by natural selection was the top priority and the sudden, complete arrival of mimetic features was an "astounding hypothesis." Under a lens Poulton had seen the hard, sharp patterns of models contrasted with the soft, transitional patterns of the mimics. The scales, colors and patterns all differed. Such approximate likeness contradicted the view holding that model and mimic originated from identical sets of pattern factors. Poulton repeated that mimicry was "the result of a series of transistional steps, some of which are still preserved." Punnett’s response, appropriately titled "Mendelism, Mutation and Mimicry," illustrated that his top priority. Numerous facts did not support natural selection as the cause of mimicry. Instead there was "strong evidence for supposing evolution to have proceeded by definite mutational stages."

Over the next year, the debate intensified. Late in 1913, Poulton remarked that Bateson and Punnett had been "dazzled and confused" by Mendelism and had "lost all perspective and all sense of proportion." Such irresponsible and "distorted vision" was unfortunate for English biological science. Although Poulton agreed that the initial variation must be appreciable, he refused to admit the saltational appearance of complete mimetic patterns. Punnett’s response claimed that Poulton was stirring up prejudice against Mendelian views. His difficulties had not been addressed and such silence suggested to Punnett that Poulton had no answers.

While natural selection explained almost all mimicry for Poulton, Mendelian genetics generally satisfied Punnett. Poulton emphasized the existence of transitional forms distributed over the range of mimic and model, while Punnett denied true transitional forms and the selective value of minute variations. As Poulton believed that natural selection was the cause of a slow, gradual development of mimetic resemblance, Punnett saw mutation as the key to a quick, sudden development of mimicry. Poulton relegated Mendelian genetics to a subsidiary position. Punnett allowed natural selection only a conservative role. The evolution of mimetic resemblance was necessarily adaptive for Poulton, but not for Punnett. Their differences seemed irreconcilable.

In April 1914 , Poulton finally responded to Punnett’s seven criticisms. In doing so, he moved toward accepting Mendelian studies of a different kind. Agreeing with the American geneticist William Castle, Poulton quoted from Castle’s book:

Poulton’s entomological research did not stop once he reached sixty years old. In fact, he published at least twenty papers related to mimicry during the 1920s. Relying upon bio-geographical data gathered from his students and entomologists around the world, Poulton continued opposing mutational and Lamarckian mechanisms and supporting natural selection throughout his latter productive years. In 1916 he commented, "The inadequacy of the hypothesis that mimetic resemblance arose at a single bound can be shown by innumerable instances of such likenessess between insects of different orders." Upon winning the Linnean Society’s Gold Medal for his contributions to biological science in 1922, the presenter called Poulton "a consistent upholder of the Darwinian position with regard to natural selection as the dominant factor in evolution." Furthermore, because he rejected speculations such as Lamarckism and pangenesis, Poulton was perhaps even "more Darwinian than Darwin himself." A decade later, Nature stated that he was "known everywhere as the most prominent living upholder of the doctrine of natural selection."

Poulton, while refining and defending his mimicry theory, clearly recognized the significance of developments taking place in biology. Not surprisingly, he saw these recent changes as triumphs for natural selection. In 1931, Poulton addressed the zoological section of the British Association in a speech entitled, "A Hundred Years of Evolution." Since 1881, when he first attended the British Association, the battles raged over Lamarckism and natural selection, and especially heredity. According to Poulton, the ‘re-discovery’ of Mendel’s work brought much controversy in the 1910s and 1920s because of the belief that "only large variations_ or as they were called, ‘mutations’. . . are subject to Mendelian inheritance and. . . small variations are not inherited at all." Finally, this controversy ended with the work of Castle and Morgan who had proven that,

Ronald A. Fisher’s recent book, The Genetical Theory of Natural Selection (1930) further strengthened the compatibility of natural selection and genetics. For Poulton, recent Mendelian research had vindicated the germinal qualities of Weismann and the natural selection of Darwin. Other victories for natural selection included the abandonment of the Thomson-Tait time limitation (i.e.,10-100 million years) with the discovery of radioactivity and emerging palaeontological evidence supporting continuous evolution.

Not surprisingly, Poulton devoted more than half of his address to mimicry. The explanation for mimetic resemblance, as it had been for more than half a century, was accumulation of small variations as caused by natural selection. Cases where the mimetic forms were more abundant than the model had made Poulton wonder whether selection in terms of survival of the fittest was always the cause of mimetic resemblance. In these cases, the

This solution, which Julian Huxley named intraspecific selection, reaffirmed the grand explanatory power of natural selection. Poulton addressed several more common criticisms of mimicry theory focussing on recent research. Research by G. D. Hale Carpenter, Frank Morton Jones, Guy Marshall, C. F. M. Swynnerton and W. A. Lamborn provided strengthened evidence of that models were unpalatable and that birds did commonly attacked butterflies. Alternative theories and criticisms of selection simply did not stand up to the mounting evidence. Natural selection still remained the best and broadest explanation for mimicry.

Poulton restated his views in several later addresses and papers. In 1937, he read the presidential address to the British Association at the age of 81. Poulton reviewed the history of evolutionary thought as recorded in the meetings of the British Association. The recent work of J. B. S. Haldane, R. A. Fisher and Julian Huxley was vitally important for showing the relationships between Mendelism and natural selection. The observations and experiments of Marshall, Lamborn, Carpenter, Jones, St. Aubyn Rogers, V. G. L. Someren, H. B. Cott, R. Carrick and others had "immensely strengthened and confirmed" the researches on mimicry and warning colors of pioneers like Bates, Wallace, Meldola, Trimen and Müller.

Amongst all the changes in biological thought, Poulton’s views remained remarkably consistent for more than half a century. From the early 1880s through the late 1930s he used morphological studies, larvae experiments on color, adaptive insect coloration and, most importantly, mimetic resemblances as evidence pointing towards the truth of natural selection. Throughout the changing fortunes of Darwin's ideas, the disputes and battles against theories of external forces, internal forces, neo-Lamarckism and Mendelism, and the comeback and eventual acceptance of natural selection in the modern evolutionary synthesis, Poulton constantly pushed mimicry as an exemplar of natural selection in action. Darwin, Wallace and Weismann remained the heroes by which Poulton compared all other biologists. His biological thought illustrates remarkable continuity in a period of immense scientific changes. Poulton may have altered his ideas slightly or accepted new evidence or new methods outside his realm, but at heart he remained a naturalist and an entomologist devoted to the cause of mimicry and natural selection.