Bryan Clarke was born on 24 June 1932. He spent much of the war in the Bahamas and, after serving in the Royal Air Force, read zoology at Magdalen College, Oxford (1956), followed by a DPhil (1961). He worked at the University of Edinburgh from 1959 to 1971, first as assistant lecturer and then reader, before moving to the University of Nottingham as foundation professor in the new department of genetics. He remained there until he retired and became emeritus professor in 1997.

Much of his research focused on snails, including members of the genus Cepaea, whose shells vary greatly in colour and banding patterns. This presents a significant challenge for evolutionary theory: if selection operates on such genetic variation, why does the population not come to consist of only a single, best-adapted, type?

In order to address this question, Professor Clarke developed the concept of frequency-dependent selection, in which the fitness of genetic types increases if their frequencies in the population diminish, thereby creating a stable equilibrium in which multiple genetic types are maintained. Equally important was his work illuminating the creation of new species though long-term study of land snails of the genus Partula on the South Pacific island of Moorea and neighbouring islands.

John Brookfield, professor of evolutionary genetics at Nottingham, paid tribute to Professor Clarke as someone for whom robust scientific disagreement never became personal: ¡°From around 1966 onwards, there was a huge debate at the heart of population genetics worldwide, which was about whether amino acid differences in proteins, both within ¨C and between ¨C species, were typically affected by natural selection. Some (the ¡®Selectionists¡¯) said that they were, while others, who were called ¡®Neutralists¡¯, believed otherwise.

ÖйúAƬ

¡°This dispute coloured the whole intellectual landscape. I always saw Bryan as a leader of the Selectionists. But, while disputes in science can become acrimonious and unconstructive, this one never did, and much of this was due to Bryan¡¯s personal qualities. He always respected his opponents, and considered their arguments on their scientific merits and never at the level of personal rivalry.¡±

Professor Clarke, who was elected fellow of the Royal Society in 1982, was also co-founder and trustee of the Frozen Ark, a charity whose work echoes that of the Millennium Seed Bank at the Royal Botanic Gardens, Kew, in preserving the genetic material of endangered animals to facilitate future scientific research.

ÖйúAƬ

He died of heart failure on February and is survived by his wife Ann, a son and a daughter.

matthew.reisz@tsleducation.com