John Maynard Smith

John Maynard Smith (1920–2004) was a British evolutionary biologist and geneticist who brought the tools of game theory into biology, transforming how scientists understand cooperation, conflict, and strategic behavior in the natural world. Trained as an engineer before turning to biology, he had an unusual facility for building formal models that captured the logic of natural selection without losing contact with empirical observation.

His most influential contribution was the concept of the evolutionarily stable strategy (ESS), which asks not what an optimally rational agent would do but which behavioral strategy is resistant to invasion by mutant alternatives — a question that maps directly onto the dynamics of evolution by natural selection. The ESS framework founded evolutionary game theory, a field that has since expanded to explain everything from animal signaling to human cooperation.

Maynard Smith also co-authored, with Eörs Szathmáry, the landmark 1995 book The Major Transitions in Evolution, which identified the repeated pattern by which independent replicators become integrated into higher-level units — the framework now known as major evolutionary transitions.