John Maynard Smith, who has died aged 84, was emeritus professor of biology at the University of Sussex and one of the world's greatest evolutionary biologists.
JMS - as he was nearly always known - was born in London but, after the death of his surgeon father, spent most of his youth with his mother's family around Exmoor. His Aunt Mary gave him a copy of Edmund Sanders's A Bird Book For The Pocket, which enabled him to put names to the birds he saw and developed in him a passion for natural history.
He was unhappy at Eton, but that was where he developed his other two abiding passions: mathematics and Darwinism. He then read engineering at Trinity College, Cambridge, and joined the Communist Party. But when the second World War broke out he ignored the party line - which, following the Hitler-Stalin pact, was that the conflict was merely an imperialist struggle - by attempting to join the army. He was rejected, later arguing that "under the circumstances, my poor eyesight was a selective advantage - it stopped me getting shot". His contribution to the war effort involved finishing his degree in 1941, and then applying it, from 1942 to 1947, to military aircraft design.
After the war he studied fruit fly genetics at University College London under the great J.B.S. Haldane, another apostate Etonian, Marxist and member of the Communist Party. JMS graduated in 1951, and from 1952 to 1965 he was a lecturer in zoology at UCL. The brutal suppression of the Hungarian revolution in 1956 finally led him, along with many others, out of the Communist Party.
In 1962, Sussex University was established, and three years later he became the founding dean of its School of Biological Sciences, a post he held for seven years and to which he was re-elected in the early 1980s.
JMS helped to illuminate so many areas in biology that it is hard to know where to begin. By introducing mathematical models from game theory into the study of behaviour he showed that the success of an individual's behaviour often depends on what other individuals do. He introduced the idea of an "evolutionary stable strategy": a strategy that, once common, cannot be bettered by alternatives. This work has completely revolutionised the way biologists think about behavioural evolution and game theory is now a commonly-used tool.
JMS also tackled one of the most vexed conundrums of evolutionary biology: why has sex evolved? His book The Evolution Of Sex (1978) pointed out "the twofold cost of sex". One way to understand this cost is to notice that sexually-reproducing organisms must produce both female and male offspring, whereas asexual, or clonal, organisms need only produce females. Since in most sexual populations around half the offspring produced are male, an asexual population with the same fecundity will produce twice as many daughters. This advantage applies generation after generation, seemingly providing a huge evolutionary advantage to clonal reproduction. Thus the problem is: why do we see so much sex in the world?
JMS was deeply committed to making evolutionary ideas widely accessible. His "little Penguin", The Theory Of Evolution (1958, 1966, 1975, 1993), inspired many leading researchers to become biologists. He took time to discuss ideas with undergraduate students and eminent professors alike, displaying almost limitless intellectual energy, even in his 80s.
In 1985, JMS retired from teaching and administration, but not from research. He wrote the influential book The Major Transitions In Evolution (1995) with Eors Szathmary, and then what he called "the birdwatchers' version", aimed at a wider public, The Origins Of Life (1999).
Another major focus of his later years was on the population structure and evolution of disease-causing bacteria. He revolutionised the field with an early publication, How Clonal Are Bacteria? (1993), going on to contribute to our understanding of a number of pathogens, including the bacterium causing TB in cattle and badgers.
In his final book, Animal Signals, published last year, JMS strove to disentangle the complex and often confusing terminology which had characterised the subject. He then challenged the widely-held assumption that there is only one correct explanation for why signallers do not "cheat". For example, if a male nightingale's beautiful song signals his quality - genetic or otherwise - to prospecting females, why do not poor-quality male nightingales pretend to be better than they are?
JMS was showered with honours, including the 1999 Crafoord Prize (awarded by the Swedish Academy of Sciences to scientists in fields not eligible for Nobel prizes) and the 2001 Kyoto Prize, Japan's highest private award for lifetime achievement.
He was famous not only for the quality of his science, but also for the way he produced it. He had no time for academic pretensions and he had a well-honed ability to cut to the heart of debate. The measure of an idea's worth was: is it true, and, more importantly, is it interesting?
He is survived by his wife, Sheila, their two sons and their daughter.
John Maynard Smith, biologist, born January 6th, 1920; died April 19th, 2004