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Sheppard, Philip Macdonald

SHEPPARD, PHILIP MACDONALD

(b. Marlborough, Wiltshire, England, 27 July 1921; d, Liverpool, England, 17 October 1976)

evolution, genetics, population genetics, medicine.

The only child of George Sheppard, a teacher of mathematics at a private school, and Alison Macdonald, Sheppard was related through his mother to the Darwin’s (being cousin, at one remove and by marriage, to Charles Darwin’s granddaughter, the poet Frances Cornford). He was educated first at Bradfield College, his father’s school, and then at Marlborough College (1935–1939). On leaving he immediately joined the Royal Air Force Volunteer Reserve and became a navigator with Bomber Command. Shot down over the North Sea on his sixteenth mission and twenty-first birthday, Sheppard spent the rest of the war as a prisoner and participated as an earth bearer in the famous “wooden horse” escape from Stalag Luft III. He returned to England after escaping from his second captors, the liberating Red Army, and entered Oxford University (Worcester College), under a dispensation that admitted returning servicemen without qualifications in Latin (he was no linguist), in 1946. Sheppard graduated in zoology in 1948 and obtained a D.Phil. under the supervision of Edmund Brisco Ford, who was a lifelong mentor and friend, for research in the ecological genetics of natural populations, in 1951.

Sheppard was then appointed as a junior research officer in the department of zoology at Oxford and spent a year (1954–1955) working with Theodosius Dobzhansky at Columbia University. His laboratory work on Drosophila remained unpublished, but the fieldwork on the moth Panaxia and the snail Cepaea became classics. Collaboration from 1952 with Cyril A. (Later Sir Cyril) Clarke, who was carrying out genetic work on swallowtail butterflies at Liverpool, led to Sheppard’s taking a lecturing appointment in the zoology department at Liverpool University (1956), followed by rapid promotion through the career grades to professor of genetics in 1963. It was here, in collaboration with Clarke, that Sheppard carried out his work on the genetics of butterfly mimicry and the prevention of rhesus hemolytic disease. He was elected fellow of the Royal Society in 1965, was awarded the Darwin Medal of the Royal Society, and was honored by the Linnean Society of London and the Royal College of Physicians.

Sheppard died at the age of fifty-five from acute leukemia, against which he had put up something of a record-breaking fight, continuing in active research with barely diminished vigor almost to the end. He was survived by his devoted wife, Patricia Beatrice Lee, whom he had married in 1948, and by their three sons.

Like so many others, Sheppard entered evolutionary research through a boyhood interest in natural history, particularly of the Lepidoptera. His graduate work on Panaxia and Cepaea showed the effects of various kinds of natural selection in controlling the genetic composition of wild populations, most notably (in collaboration with Arthur J. Cain) that what had frequently been seen as the trivial characteristics of banding and color on snail shells adapted the snails to their background habitat. The study of Panaxia, a continuation of a long-term project by R. A. Fisher and Ford, was an exceptionally thorough examination of the dynamics of a gene in a natural population. This work, together with that carried out in Ford’s laboratory at the same time by Bernard Kettlewell, was extremely influential in establishing the view of evolution that descended from the writings of Alfred Russel Wallace, August Weismann, and Fisher: that natural selection was the all-powerful process in generating evolutionary change. That view continued to be challenged; but there is no doubt that these experimental results, even if they did not and could not finally establish that selection did everything of significance, did succeed in demonstrating that selection could and did produce evolutionary changes, and that in the process it generated organic diversity. Before this work, it could be stated with some justice that the theory of evolution by natural selection rested largely on conjecture.

Sheppard’s interests therefore centered on the experimental study of questions raised by the neo-Darwinian “modern synthesis” of genetics and evolutionary theory during the first half of the century, particularly of the action of natural selection in shaping both the organism and its genes. He summarized his views elegantly in Natural Selection and Heredity (1958), a work that was at once a student text and an original monograph, At Liverpool, in collaboration with Clarke, he produced a classic solution to a long-standing enigma of Darwinism, the evolution of mimicry. By anatomizing the genetics of mimetic patterns in the tropical butterflies Papilio dardanus and P. memnon, and Heliconius melpomene and H. erato, a monumental breeding project extending from 1956 until after Sheppard’s death and involving international teams of collaborators, they synthesized the extremely gradualistic views of Darwin and Wallace with the theories of the old mutationist school of evolution, showing how the adjustment (“modification of gene action”) of the genetic background to an existing large mutation could refine the mimetic resemblance and alter its genetic architecture, thus resurrecting the long-forgotten view that adaptations of this kind arose in two stages: mutation and modification. Particularly original was their discovery of “supergenes;” tightly linked blocks of functionally independent genes, all controlling different aspects of the mimetic pattern.

Hoping to show that natural selection was still active in human populations, and aided by a large medical team, Clarke and Sheppard investigated the correlations of blood groups with disease. They had particular success with the ABO groups, and the study of such antigen-related disorders was later to become a major field of medicine. Believing also that the rhesus blood groups were controlled by a supergene similar to that found in mimetic butterflies, they then turned their attention to the chief form of natural selection known to act on these blood groups, hemolytic disease of the newborn. This led to an enduring advance in pediatrics: the prevention of this condition—a major cause of miscarriage, infant death, and brain damage—by injecting with rhesus antibody those mothers known to be at risk.

Sheppard’s distinguished position in both medicine and population biology led to his being invited by the World Health Organization to investigate the population genetics of insecticide-resistant mosquitoes in Southeast Asia. He also undertook field-work on mimicry in South America. Since they lived in the most polluted part of Britain, the Liverpool team also carried out significant work on natural selection and industrial melanism in moths.

Sheppard had the ability to make everything he touched interesting, both as a researcher and as a teacher; all his best work was done in collaboration, his keen mind, his friendly lack of affectation, and his dedication inspiring the best in his teammates. Compromise was foreign to his scientifically acute mind, and his impatience with politically motivated action and inaction made him less effective among scientific bureaucrats at World Health Organization headquarters. Although he trained surprisingly few graduate students, his influence in English population biology was widely felt through his book, his undergraduate teaching, perhaps his teaching films for television, and his guidance of younger researchers; it was said that he had a superb facility for suggesting the next experiment. His was a wider influence than was immediately apparent because of his ethical refusal to add his name to a paper unless it was truly his.

BIBLIOGRAPHY

I. Original Works. Among his 150 scientific publications. Sheppard’s only book was Natural Selection and Heredity (London, 1958; 4th ed., 1975); he also edited a collection of exercises in Practical Genetics (Oxford, 1973). The annotated Clarke-Sheppard-Turner collection of genetic broods of Papilio and other species in the British Museum (Natural History), London, includes correspondence from the period 1952 to 1953. At the time of writing, Sheppard’s correspondence and scientific papers are in the department of zoology. University of Liverpool (Professor Arthur J. Cain), and a small collection of correspondence with John R. G. Turner is being donated to the John Innes Institute, Norwich, England.

II. Secondary Literature. Bibliographies, not totally overlapping, are by John R. G. Turner, in Journal of the Lepidopterists’ Society, 31 , no. 3 (1977), 205–212; and that accompanying the biography by Cyril A. Clarke in Biographical Memoirs of Fellows of the Royal Society, 23 (1977), 465–500, the first of these listing posthumous papers. Additional obituaries were published by Arthur J. Cain in University of Liverpool Recorder, 74 (1977), 4–7, and in Heredity, 40 (1978), 317–319: by B. C. C. [Clarke], in Nature266 (1977), 201; and by Cyril A. Clarke, in The Times (London), 19 October 1976, p. 14. Eric E. Williams’ The Wooden Horse (London, 1949; nonfiction ed., 1979) gives a detailed account of the famous escape, although the “Philip” who figures in the book is a different person.

John R. G. Turner

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