Cain, Arthur James

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(b. Rugby, Warwickshire, England, 25 July 1921;

d. Liverpool, United Kingdom, 20 August 1999), evolutionary biology, zoology, malacology, systematics, history of taxonomy.

Cain was a disciple of evolutionary synthesis. During the 1950s he and Philip Sheppard produced a strong case study of natural selection using the land snail, Cepaea. Cain became a leading advocate of selection and adaptation. He later contributed to taxonomic theory and the history of systematics.

Career in Brief . Cain was born into a working-class family. He attended Lawrence Sheriff School, Rugby, a selective boys’ grammar school. In 1939 he received an academic scholarship to Magdalen College, Oxford, graduating in 1941 with a first-class honors degree in zoology.

Cain saw military service between December 1941 and November 1945, commissioned as second lieutenant in the Royal Army Ordinance Corps. In 1942 he was promoted to captain and transferred to the Royal Electrical and Mechanical Engineers. Much of his service involved radar and antiaircraft batteries in the Orkney Islands.

Cain returned to the Department of Zoology, University of Oxford. He obtained his MA (1947) and PhD (1949). From October 1946, he was departmental demonstrator. In January 1949 he was university demonstrator in animal taxonomy. Reportedly, this appointment, which lasted until 1964, was created after specific lobbying from the Systematics Association (a group committed to furthering all aspects of systematic biology). Concurrently, Cain curated the zoological collections at University Museum (1954–1964) and was lecturer in zoology, St Peter’s Hall, Oxford (1958–1961).

In 1964 Cain was appointed professor of zoology, University of Manchester. This was a considerable promotion, and it removed Cain from personality conflicts growing in Oxford. Cain later delighted in the irony of his appointment: his chair’s previous occupant, Herbert Graham Cannon, was a neo-Lamarckian and opponent of Darwinism. At first Cain thrived in Manchester, but politics and more personality conflicts took their toll. In this period, Cain undertook several long-term projects abroad, both relieving and aggravating the situation.

Cain soon moved to the University of Liverpool, appointed Derby Professor of Zoology in 1968. Sheppard had moved to Liverpool in 1959, and encouraged further expansion of the genetics and zoology programs. Cain retired in 1989.

As a person, Cain kept a small circle of close friends, largely professional colleagues and former students. Bryan Clarke, a student, aptly described Cain as having “an incendiary enthusiasm for evolutionary biology, a tendency toward wrathful indignation, and a deep contempt for administrators, particularly those who had once been scientists” (Clarke, 1999, p. 872). His “combative style and changeable moods” earned Cain many enemies and contributed to his delayed election into the Royal Society (1989)” (Clarke, 1999, p. 872). Lawrence Cook (2000), another student, noted, “No one ever accused him of being a good diplomat or a good administrator.” At the same time, students and colleagues widely praised Cain for his encyclopedic knowledge, his demanding but inspirational mentoring, and his passion for evolutionary biology.

Department of Zoology, Oxford . Cain’s graduate training concentrated on histology, the study of tissue. Returning to Oxford in 1945, he wanted to study ecology and genetics, but he later recalled being “scared stiff” by the competition between tutors in these areas (Edmund Brisco Ford and Charles Elton). Cain turned to biochemistry, studying under John Randal Baker. Cain admired Baker greatly, and his mentor had lasting influences on Cain’s approach to research.

Cain’s doctoral research was dictated by Baker’s interest in methodological precision. How do techniques for studying cells alter them from a natural state? Baker worried over the precise limits of conclusions he could draw from laboratory data, and he was scrupulously critical when interpreting results. What artifacts might lead him astray? What were the limitations of his data? What were possible sources of error?

This critical approach proved crucial in Baker’s study of the Golgi apparatus. Disputes with other histologists over the function of this organelle drew attention to the precise value of histological techniques for identifying types of lipoids. Baker assigned Cain the task of investigating the validity of such tests. In the process, Cain refined procedures for distinguishing acidic and neutral lipoids. (These later proved useful in studying cell physiology, though Cain did not pursue that avenue himself.) Baker was impressed by Cain’s ability to analyze methods and determine their precise contributions to knowledge.

Cain’s interests in natural history, ecology, and evolution predated the war. He was quick to seek the position of demonstrator in animal taxonomy when Oxford offered it for 1949. Recognizing he had no graduate-level qualification in systematics, Cain requested and received leave to study for six months at the American Museum of Natural History, under Ernst Mayr. Cain’s participation in Mayr’s program most likely was secured through David Lack.

Cain’s apprenticeship with Mayr steered his biological interests, and Cain often returned to ornithological projects. While at the museum, Cain studied geographic speciation in Australian parrots and Malaysian pigeons. In 1953 he led a small expedition to the British Solomon Islands, collecting geographical varieties and searching for sibling species. As Cain later recalled, collecting was done according to an “evolutionary point of view,” that is, in line with the intellectual framework advocated by Mayr. Cain’s notes from his apprenticeship with Mayr formed the core of his 1954 book Animal Species and Their Evolution.

Natural Selection in the Land Snail, Cepaea . Beginning with Sheppard in the 1950s, Cain researched the evolution of the land snail, Cepaea. His interest in this model organism lasted forty years. The first years of research had a dramatic impact on evolutionary biology. Cain and Sheppard began their collaboration in 1949, collecting Cepaea from different microhabitats near Oxford. Cepaea is a polymorphic species. Cain and Sheppard sought correlations between morphology and environment, focusing on shell color and banding patterns, that is, on causes of conspicuousness to visual predation. Finding no correlation between these qualities and habitat type would have reinforced the commonly held view that banding pattern and coloration were adaptively neutral, that they provided no advantage to snails in their struggle for existence.

In fact, Cain and Sheppard found the reverse: a strong correlation between habitat, banding pattern, and color. This could be explained in terms of natural selection for inconspicuousness. When backgrounds were uniform, for instance, banding made snails easier for predators to see; when backgrounds were heterogeneous, banding made snails harder for predators to see. Cain and Sheppard thought they had a clear demonstration of selection. They also thought this explained why Cepaea was polymorphic, as selection in different parts of the range drove adaptations in different directions.

Importantly, Cain and Sheppard used their Cepaea work to speak authoritatively about general evolutionary theory. Their opposition held the view that traits normally were adaptively neutral. Against this view, Cain and Sheppard forcefully argued three points. First, natural selection was the principal cause of evolution. Second, adaptation was the best way to understand why a species evolved its traits. Third, supposedly neutral traits must be reexamined because detailed study almost certainly will produce a selection-based interpretation. For Cain, any claim that a trait had no adaptive value should be understood only as a statement of ignorance about the complexities of biological worlds.

This Cepaea research became a classic case study, providing supporters with a clear example of adaptation in nature. Though their conclusions were repeatedly challenged (for example, by French evolutionary biologist Maxime Lamotte), the broad significance of this research was in the conversion of Cepaea from an opposing to a supporting example of selection. Indeed, Cepaea become iconic, at least among those in English-speaking countries. This act of redemption followed other celebrated reclamations (for example, Lack on Galapagos finches, Theodosius Dobzhansky and Marion L. Queal on Drosophila), each drawing interest away from neutral characters and random drift as major features of evolution.

Cain and Sheppard’s Cepaea research also bolstered “ecological genetics” and the “new” natural history as it developed in postwar Britain. These approaches combined field studies with laboratory work in genetics and physiology. It used experimental tests and correlative studies, such as fossil evidence, to complement observational results from the field.

Cain’s interest in Cepaea lasted forty years and was not limited to studying selection. Additional research investigated the genetics of banding patterns and coloration, the relation between physiology and external morphology, microecology, variation in shell shape, seasonal changes in selection pressures, and the process of visual selection by predators, especially birds.

In the early 1960s Cain produced the first description of “area effects” in natural populations. This phenomenon concerned the distribution of variations. Cain occasionally found characters shared across adjacent populations but that could not be correlated with obvious features common to the various habitats. Cain had difficulty explaining these observations, though he was certain selection was somehow key. Perhaps, he supposed, area effects were caused by selection for environmental factors that human senses could not easily detect. Alternatively, perhaps they are caused when characters genetically linked to the ones observed are actively selected; the latter simply being dragged along. Cain collaborated with John Currey in this research but rarely moved beyond simply describing these patterns.

In 1988 Cain published his last major research paper on Cepaea, reporting on a twenty-year study of laboratory colonies in which population size was sharply reduced at random points in time. This simulated genetic bottlenecks and tested the prediction of some mathematical population geneticists that random sampling could lead to genetic revolutions—the “founder effect.” Cain reported a failure to confirm the prediction of a founder effect. Instead, genetic diversity more or less rapidly recovered. This study was a final piece in Cain’s career-long effort to downplay genetic drift in evolution.

Cain and Sheppard never explained their decision to start Cepaea research. Both agreed it was Cain who focused attention on Cepaea as a model organism. Both also admitted a predisposition toward adaptive explanations. Studying polymorphism as they did would have seemed obvious in Oxford during the 1940s. It fit nicely into the “experimental adaptationist programme” (as the historian William B. Provine refers to it) actively underway at Oxford.

Adaptationism . The origins of Cain’s convictions about selection are obscure. In autobiographical notes he complained about prejudices against selection before World War II. This was especially true when closely related species were studied, with differences frequently attributed to nonadaptive characters.

Cain never doubted his selectionist position, and he happily carried the banner for his cause. In a series of letters to Nature during 1951, for instance, Cain eagerly argued with the zoologist George Stuart Carter over “so-called non-adaptive or neutral characters in evolution.” Neutrality was a presumption and not a demonstrated conclusion, he demanded. Adaptedness should be preferred as a default hypothesis because it is more likely to be true. Only when positive evidence for random processes was presented or exhaustive tests failed to support adaptive explanations should other explanations be considered. In such disputes, Cain applied the same critical attitude Baker had used in histology: castigating writers for drawing conclusions far beyond their specific evidence and for being too quick to generalize on only a few examples. However, as the philosopher Roberta Mill-stein has shown, Cain demanded far more rigor for studies of neutrality and drift than he did for selection.

Cain applied his adaptationism to taxonomy by stressing the importance of constancy. Constant characters offered stable tools for taxonomic decisions, he said. Constancy could not be a passive quality in nature, as mutation and recombination constantly introduced variation. It had to be actively maintained, Cain argued, hence its presence indicated the work of natural selection. Cain was so convinced of this point that he proposed a heuristic. In the absence of contrary evidence, naturalists should “treat constant characters as probably having a definite selective meaning” (Cain, 1959, p. 14).

In 1964 Cain published his farthest reaching proposals about adaptation. In “Perfection of Animals,” he shifted from the role selection plays shaping single features to the role it plays shaping whole organisms. On one level, this paper was a broadside against the increasing dominance of reductionist molecular biology. Cain defended the alternative organism-in-environment perspective of evolutionary biology.

More subtly, Cain had broken away from thinking common descent was the most important determinant of form. Instead, he thought no character was so entrenched that it could not be reshaped during evolution. Whole body plans were subject to reshaping by natural selection. Cain explained, “the major plans of construction … are soundly functional and [are] retained merely because of that. … Their plans are adaptive for broad functional specializations; the particular features of lesser groups are, as has long been agreed, adaptive for more particular functions” (Cain, 1989, p. 4).

Cain’s emphasis on selection certainly had critics. To some, he became the caricature of an adaptationist paradigm. Cain’s conflict with Stephen Jay Gould, whose early study of recapitulation theory was an early broadside against Cain’s “perfection” thesis, was particularly sharp. Gould and Richard C. Lewontin’s attack on “spandrels” and the “Panglossian paradigm” certainly had Cain in mind. For his part, Cain regularly referred to Gould as merely a “propagandist.”

A Disciple of Synthesis . Cain began his career just as the evolutionary synthesis coalesced into a distinct movement in the life sciences. His position at Oxford, and his experiences with Mayr in New York, perfectly placed him to be influenced by, and to influence, the movement on both sides of the Atlantic.

In 1954 Cain published Animal Species and Their Evolution. Narrowly, this book functioned as a primer on taxonomic theory, condensing Mayr’s Systematics and the Origin of Species (1942), slightly modified. At its center was the polytypic species and the biological species concept. Cain defended the importance of geographic isolation in the formation of species, and he invoked selection-causing local adaptation as the key mechanism of evolution. Main examples came from Cain’s own research. He gave no important role to neutral characters or genetic drift. Sympatric speciation was rejected for animals (at the least it was not yet demonstrated), but accepted for plants, via polyploidy. Cain elevated the subspecies (geographically definable, taxonomically distinct populations within a species) to the status of sibling species.

Animal Species departed from expectations in two important ways. Although Cain accepted the biological species concept as a criterion for species in evolutionary terms, he knew it had important practical limitations. As others did before him, Cain supplemented the biological species concept (he called it “biospecies”) with additional concepts, including: “morphospecies” (defined solely by lists of characters, such as from museum collections), “pale-ospecies” (successive stages in a chronological sequence), and “agamospecies” (species in asexual organisms). This terminology once again reflected Cain’s attention to methodological precision. Like many taxonomist colleagues before him, Cain struggled to relate taxonomic decisions and statements made by colleagues using different, often unexplained, methods. Cain worried about comparability and consistency. He wanted to know—to know precisely— what kind of species he was working with.

Cain’s book sold well and broadened his audience. A decade later, he used the same book series to promote others, serving as editor of the Biological Series for Hutchinson’s University Library (1967–1975). Cain oversaw publication of at least ten books, including Lawrence Cook’s Coefficients of Natural Selection (1971), Martin Rudwick’s Living and Fossil Brachiopods (1970), and Robert McNeill Alexander’s Functional Design in Fishes(1967).

Theories of Classification . Cain’s thinking about species concepts led him to fundamental problems, which eventually brought him to reject evolutionary systematics and binomial nomenclature. Around 1960 Cain identified with an alternative approach in the field, numerical taxonomy; however, this association was short-lived.

In Animal Species, Cain wrote frankly about taxonomic ranks. What’s the difference, he asked, between taxonomic units such as “order” and “family”? Ultimately there were none, he said. Ranks in normal Linnean hierarchies referred to no standard unit of diversity, offering instead only convenient pigeonholes for organizational purposes.

But the discovery of evolution forced taxonomists to adopt another view about ranks. The facts of descent and phylogeny introduced notions of “relatedness” and “affinity.” Organisms assigned to one group, by implication, are claimed to be more related to each other than to those assigned to different groups.

In the mid-1950s Cain started questioning the need for taxonomy to make claims about affinity and relatedness while simultaneously grouping nature into organizational units. Behind Cain’s complaint, again, was his long-standing concern for precision. When taxonomists placed two morphospecies in the same taxonomic family, he worried, they did not necessarily mean to imply those morphospecies were more related to each other than to morphospecies outside that family. However, relatedness was precisely what any outsider would conclude, given a rudimentary knowledge of evolution.

Cain focused his frustration onto one taxonomic unit, the genus. (For instance, Homo is the genus name for a number of species, including Homo sapiens and Homo erectus.) Formal rules of nomenclature absolutely required all species names to include two pieces: a generic name (Homo) and trivial name (sapiens). To Cain, this requirement forced taxonomists to make a claim about affinity and relatedness even when they wanted only to make identifications. Consider this example: suppose one finds a fossil that seems much like the humanlike apes already known. One wants to give it a formal name, but also wishes to avoid implying a close connection with Homo or any other group. The rules, Cain complained, required one of two solutions: either make some generic assignment despite any reservations (for example, call it Homo even if it is thought that H. sapiens or H. erectus might not be its closest relations), or invent a new generic name and worry about affinities later. Neither solution seemed honest to Cain. Why be compelled to make an evolutionary claim when all he wanted was a standardized reference name for a single specimen? This logic was the foundation for Cain’s later rejection of binomial nomenclature.

Cain also drew taxonomists’ attention to a subtle and ultimately more worrying problem. The naming and comparing work taxonomists undertook occurred using incomplete information. For many of the similarities used in that routine, it often was difficult to identify which resulted from relatedness and which resulted from convergence (the independent evolution of similar traits in response to similar environmental challenges). This was aggravated by the frequent heavy emphasis placed on only a few characters in each group. To Cain’s mind, this gave too much room for self-deception (thinking similar forms were related when in fact they had converged) and subjectivity. Cain wanted rigorous, independent tests combined with more explicit discussion in taxonomic decision making.

Cain’s desire for increased rigor led him to his second substantial break in systematics. Because taxonomic decisions based on only a few characters was suspect, he argued, organisms should be compared “as a whole.” He meant this in the literal sense: animals as integrated, functioning wholes. He also meant it as the study of all parts, as there was no a priori reason to privilege some characters over others. Using comparisons of all characters, he said, was the only “natural” basis for taxonomic decision making.

Cain’s position was similar to advocates of “numerical taxonomy.” For a few years, Cain presented himself as part of that campaign, complaining, as others did, that “phylogenists” forced evolution and systematics into an unhappy marriage. Cain soon broke with that movement, however. He complained it had became increasingly abstract and computational while less concerned with whole organisms living in natural habitats.

Cain had long-standing interests in the history of systematics, including studies of Aristotle (384–322 BCE), John Ray (1627–1705), Carolus Linnaeus (Carl von Linné, 1707–1778), and Constantine Samuel Rafinesque (1783–1840). Cain interpreted such writers in ways that added credibility to his own points of view. For this reason, and because he tended to write papers that seemed little more than long series of long quotations from original sources, Cain’s historical work has not fared well with historians. Notably, Cain’s technique once again followed his Oxford mentor, as when Baker wrote about the history of cell theory. Mary P. Winsor provides a superb analysis of Cain’s historian interests.

Naturalist in the “Best Sense of That Word.” . Cepaea made Cain famous, but his zoological interests had much wider scope. Students called Cain one of the best naturalists of his generation. After Cepaea, he collected around the globe, including eastern North America (1950), British Solomon Islands (1953), and British Guiana (1959). Malacology (the study of mollusks) was his first and deepest passion. Ornithology (the study of birds) was second.

In the early 1960s Cain’s research shifted to Lake Kariba (between Zambia and Zimbabwe), formed on the Zambezi River after completion of the Kariba Dam in 1960. In 1962 Cain was Oxford’s representative on the Inter-Universities Committee for Research at Lake Kariba. He also served as the committee’s scientific secretary in the United Kingdom. In his capacity as secretary, Cain repeatedly traveled to Africa during 1962–1965, conducting additional research in Kariba, then Johannesburg, South Africa. In 1965 he studied bird ecology in Serengeti National Park, Tanzania.



With Philip M. Sheppard. “Selection in the Polymorphic Land Snail Cepaea nemoralis.” Heredity 4 (1950): 275–294. First paper in research program on natural selection in the wild.

Animal Species and Their Evolution. London: Hutchinson’s University Library, 1954.

“Function and Taxonomic Importance.” In Function and Taxonomic Importance: A Symposium, edited by Arthur J. Cain, 5–19. London: Systematics Association, 1959.

“The Perfection of Animals.” In Viewpoints in Biology, vol. 4, edited by John D. Carthy and C. L. Duddington. London: Butterworth, 1964. Reprinted in Biological Journal of the Linnean Society 36 (1989): 3–29.


Clarke, Bryan. “Obituary: Arthur James Cain (1921–99).” Nature 401 (1999): 872.

Cook, Lawrence. “A. J. Cain FRS 1921–1999.” Bulletin of the Malacological Society 34 (2000): 2–3.

Millstein, Roberta L. “Concepts of Drift and Selection in ‘The Great Snail Debate’ of the 1950s and Early 1960s.” In Descended from Darwin: Insights into American Evolutionary Studies, 1900–1950, edited by Joe Cain and Michael Ruse. Forthcoming. Thorough discussion of the Cepaea research and its critics.

Winsor, Mary P. “Cain on Linnaeus: The Scientist-Historian as Unanalysed Entity.” Studies in the History and Philosophy of Biology and Biomedical Sciences 32 (2001): 239–254. Splendid study of Cain’s use of history of taxonomy to express his own taxonomic theory. Also includes useful biographical information.

Joe Cain