Fisher equation

The Fisher equation is a mathematical formula that describes how a beneficial gene spreads through a population over time, showing that faster-spreading genes must come with a cost in terms of reduced survival or reproduction. Named after the pioneering geneticist Ronald Fisher, this equation reveals a fundamental trade-off in evolution: organisms can't simultaneously maximize how quickly they reproduce and how long they survive. This concept helps scientists understand real-world evolutionary patterns, from why some species have many offspring with short lifespans to why others invest in fewer but longer-lived children.