I first met Arthur Cain when interviewed as a prospective research student. After some wary sparring on both sides I mentioned that the animal I proposed to study was at the edge of its range, and therefore likely to show clear evidence of ecological limiting factors. 'Ah, peripheral populations', he said, and I was treated to a 40 minute monologue on all aspects of the subject. After that I was in, and learned that this was one of his favoured patterns of communication. Generations of research students remember Arthur holding forth and developing his ideas during tea and coffee breaks. A vast range of biological topics was covered and the enthusiasm was infectious.

After a spell in the forces during the war, Arthur returned to Oxford to do research in cell chemistry. This was followed by practical ornithology in the Solomon Islands and work on bird taxonomy with Ernst Mayr in New York. He returned to Oxford, became Reader in Taxonomy, was involved in the beginnings of phenetic analysis and developed a deep interest in the theory of classification from Aristotle to the present day, which continued to his latest work (e.g. Cain, 1997). From Oxford he moved to Manchester and then to Liverpool to Chairs in Zoology and also spent some extended periods in Guyana, the Serengeti and the Philadelphia Academy of Sciences. He was elected Fellow of the Royal Society in 1989.

Interest in molluscs began in association with Philip Sheppard, when they realized that Cepaea nemoralis was an ideal subject for experimental study of visible polymorphisms. Using descriptions of phenotype which reflected what a predator might see, rather than the permutations of characters recorded by earlier malacologists, they were able to show that in mature wooded and agricultural habitats there was a general matching of phenotype to background and that the most important predator, the Song Thrush, selectively removed the most conspicuous forms. This work is summarised, and its implications discussed, in Cain and Sheppard (1954). Their programme of breeding greatly extended knowledge of the genetic basis of variation in the species. Strong selective pressure appeared to be the determining factor in the polymorphism. This conclusion found much favour in the Oxford of the time, but brought Arthur face to face with current arguments about the importance of random processes in evolution. His response was to write The Perfection of Animals (1964), a closely reasoned essay stressing the adaptive value of the design plans of the major groups of animals. This was later republished in a festschrift issue of the Biological Journal of the Linnean Society (vol. 36, 1-226, 1989).

Further field studies indicated that Cepaea did not always show an association of colour morph and background, but exhibited so-called area effects: patches of constant frequency bounded by patches with different genetic composition (Cain and Currey, 1963). The possible significance of locus interaction at levels of gene action uninfluenced by visual appearance had to be considered. Many research students and independent colleagues took to Cepaea work, extended the surveys and opened up fresh paths, so that it became a focus for resolution of new ideas in a range of areas of population genetics. It stimulated a contribution by the distinguished founding father of the subject, Sewall Wright (1965), while the emphasis by Bryan Clarke (1962 and later) on the frequency-dependent nature of the selection had a significant effect on future theory and experiment.

The ebullience and enthusiasm with which Arthur approached a subject had its negative side; he was sensitive to disagreement and tended to take it as personal criticism. This had one compensation, because to get over a perceived setback he would turn to a completely different topic. The study of shell shape (Cain, 1977) was one example. Using the simple relation of shell height to shell breadth he surveyed the variation in gastropods, showed that modern groups are strongly bimodal in shape, that this pattern has evolved and that powerful inferences can be made about the adaptive value of shape. The method can then be extended to analyse the structure of island and regional faunas and indicate the extent to which niches are filled (Cain, 1981). The basic information was available to all, but Arthur had the insight to make it matter in evolutionary biology.

Another important series of studies concerned the broader associations of molluscan colour and polymorphism with habitat (e.g. Cain, 1988). It is difficult to unravel the factors maintaining polymorphism in individual cases, and to put relative values on the various causative agents. The comparative method surveying a broad range of species and situations is a powerful alternative approach which has been undervalued, and Cainís work provides strong evidence for selective predation as a dominant explanatory factor.

No-one ever accused him of being a diplomat or a good administrator, and the creation of a heavily funded research school never interested him. Nevertheless, his influence was great, and there is a large and varied group of people working today who are in some respect his academic descendants. That is so because he contributed a sense of excitement about evolutionary biology, a continuous flow of ideas, and a ready ability to inspire. His career was characterised by manifest intellectual integrity together with a feeling for the subject derived from the nineteenth century giants whose work he admired.

Lawrence Cook

The Manchester Museum

References:

Cain, A.J. 1964. The perfection of animals. In Carthy, J.D. & Duddington, C.L. (eds.) Viewpoints in biology 3, 26-63. Reprinted in Biol. J. Linn. Soc. 36, 3-29 (1989).

Cain, A.J. 1977. Variation in the spire index of some coiled gastropod shells, and its evolutionary significance. Phil. Trans. R. Soc. Lond. B 277, 377-428.

Cain, A.J. 1981. Variation in shell shape and size of helicid snails in relation to other pulmonates in faunas of the Palaearctic region. Malacologia 21, 149-176.

Cain, A.J. 1988. The colours of marine bivalve shells with special reference to Macoma balthica. Malacologia 28, 289-318.

Cain, A.J. 1997. John Locke on species. Archives of Natural History 24, 337-360.

Cain, A.J. and Currey 1963. Area effects in Cepaea. Phil. Trans. R. Soc. Lond. B 246, 1-81.

Cain, A.J. and Sheppard, P.M. 1954. Natural selection in Cepaea. Genetics 39, 89-116.

Clarke, B. 1962. Balanced polymorphism and the diversity of sympatric species. In Nichols, D. (ed.) Taxonomy and geography. 47-70. Publ. No. 4. Systematics Association, London.

Wright, S. 1965. Factor interaction and linkage in evolution. Proc. R. Soc. Lond. B 162, 20-104.

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