The passing of Cyril Clarke marks the end of the era of great medical all rounders. His career as a clinician ranged through life insurance practice, medical specialist in the navy, consultant physician, and later Professor of Medicine in Liverpool, and, finally, President of the Royal College of Physicians of London. His research contributions were equally broad based, spanning his classical work on mimicry in swallowtail butterflies to his enquiry into longevity by tracing and studying the lifestyles of centenarians who had received congratulatory messages from the Queen. He was one of the first in this country to appreciate that medical genetics, far from being a discipline which focuses on rare and esoteric diseases, has a major role to play across every aspect of day to day clinical practice. This led him to establish the Nuffield Unit of Medical Genetics in Liverpool, which became a stable for many who went on to develop this field throughout the United Kingdom and elsewhere.

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But Cyril Clarke's most important contribution to medicine, and one that reflects his flair and willingness to chance his arm in problems which were often outside his field of expertise, was his inspiring leadership of the Liverpool team that discovered how to prevent rhesus haemolytic disease of the newborn, one of the major advances in preventive medicine of the last half century. This work typified his unwillingness to be deterred by the gloomy prognistications of experts in their fields, who often told him that his thinking was way off the mark, and his instinctive gift for what Peter Medawar called “the art of the possible”, reflected in his ability for sensing the quality of his younger colleagues and the science that they were pursuing.

Cyril Astley Clarke was born in 1907. His father, Astley Vavasour Clarke, was a physician at the Leicester Royal Infirmary and one of the first to use x rays in this country; his grandfather was senior surgeon to the same hospital. He was educated at Oundle, Caius College, Cambridge, and Guy's Hospital Medical School. After three years in life insurance practice, which allowed him time to indulge in his passion for sailing and offered him the opportunity to examine Winston Churchill, he enrolled as a medical officer in the RNVSR and served throughout the war in the navy, ending his service by writing one of his first papers, on the neurological complications of malnutrition that he observed in British prisoners of war in Hong Kong.

After the war Cyril moved to Liverpool where he became Consultant Physician at the David Lewis Northern Hospital. Despite busy hospital and private practices he, together with his long time friend and collaborator P M Sheppard, began a series of classical experiments on the genetics of swallowtail butterflies, work which later stimulated his interest in medical genetics. The success of the team of young clinical research workers that built up round him left him less time for his clinical practice, and he was appointed Reader in Medicine at the University of Liverpool and, in 1963 on the retirement of Henry Cohen, he became Professor of Medicine, a post that he held until 1972. He founded the Nuffield Unit of Medical Genetics, which he directed from 1963 to 1972. On the year of his retirement he was elected President of the Royal College of Physicians of London, a post he held with great distinction and flair until 1977. From 1977 to 1983 he served as Director of the College's Medical Services Study Group, and from 1983 to 1988 was Director of its Research Unit. Among his many other activities he served as President of the Royal Entomological Society and, much to his delight, President of the British Mule Society. He spent his later retirement in Liverpool continuing his work on the genetics of butterflies and in a characteristically broad range of medical research.

Cyril's interests in butterflies, which started as a childhood hobby, was reawakened while he was serving in the navy and visited Australia. He had a childhood ambition to breed the swallowtail butterfly, Papilio machaon, and he developed a technique for making them mate by hand. By chance, he obtained a North American swallowtail, Papilio polyxenes, and was able to mate this with P machaon. He produced F₁ hybrids, and then backcrosses, and hence discovered that their colouring reflects only a single gene difference between the two species. Philip Sheppard read of this work and contacted Cyril and thus started a long standing and extremely productive collaboration on the genetics of mimicry in tropical butterflies. The two of them also became interested in moths and industrial pollution and followed up the observations of Bernard Kettlewell on the adaptive changes in the colouring of moths in relationship to pollution. Starting in 1959, and working every year up to 1994, Cyril and his colleagues caught moths in June and July using a mercury vapour lamp. Overall, they collected 17 648betularia and were able to relate the proportion of carbonaria to the level of pollution.

There seems little doubt that Cyril's interest in medical genetics was stimulated by his work on butterflies. It was Philip Sheppard who suggested to him that blood group genetics might be a productive way into this field. Cyril started by examining the relationship between blood groups, secretor status, and duodenal ulcer and then turned his attention to rhesus haemolytic disease. After his student Ronald Finn confirmed the observation that ABO incompatibility between mother and fetus is protective against haemolytic disease in the newborn, and hearing of the transplacental passage of red cells from the fetus to the mother, Cyril and his colleagues evolved the notion of injecting mothers with anti-rhesus antibody (anti-D). Studies using male volunteers were initially unsuccessful because they were carried out with complete anti-Rh. But, at the suggestion of Ruth Sanger, they were able to prevent immunisation in a further set of volunteers by using incomplete anti-D. The story of this success was heralded in a local Liverpool newspaper with the headline “Men of Merseyside Mothers To Be”. The rest of this story is well known.

Cyril was a caring if slightly eccentric clinician, very much of the old school, who believed in minimal intervention. His advice to his new house staff on the use of drugs came, he claimed, straight from the mouth of one of his teachers at Guy's, who, as he got older, restricted his personal pharmacopoeia to morphia and sodium bicarbonate, and was not too liberal with the bicarbonate.

As Professor of Medicine he led his department with a light touch, preferring to let bright youngsters go their own way, but always around if they needed support. His remarkable flair and enthusiasm, and his ability to sniff out talent and to pick research areas of importance, was undoubtedly the major factor which led to the wonderful achievement of the rhesus team, and to the success of the Department of Medicine at Liverpool and its major influence on the development of medical genetics.

As a person, Cyril was a complex mixture of a life long schoolboy, constantly bubbling with enthusiasm and new ideas, and yet at the same time he could appear to be rather distant, so that his students and junior staff sometimes found him difficult to approach and not a little terrifying. This was undoubtedly a reflection of his innate shyness; as they got to know him better his extraordinary warmth became apparent. He was extremely loyal to his staff and supported them throughout their careers, usually behind the scenes and often without their knowledge. In 1935, he married Frieda, or Féo as she was always known. Féo became an integral part of all Cyril's work and his many other activities, which ranged from crewing for him in his annual small boat racing (not a relaxing pastime since Cyril had been an Olympic trialist and hated losing) to breeding swallowtail butterflies in captivity. It was a remarkable partnership; Cyril never fully recovered after Féo's death in 1997. They are survived by three sons.

Cyril's work was widely recognised. He was elected FRS and received many national and international awards. At the age of 88 years, still busy at his research, he wrote that he would very much like to know why butterflies have an XX chromosome complement in males and XY in females, yet the latter live much longer than the tempestuous XX males. “God moves in a mysterious way” he concluded. Certainly there can have been few more mysterious phenomena than the multifaceted talents, flair, and complexity and warmth of character of the man who wrote these words.