Jordana Cepelewicz | Quanta
In 1964, the evolutionary biologist William D. Hamilton seemingly explained one of the greatest paradoxes in biology with a simple mathematical equation. Even Charles Darwin had called the problem his “one special difficulty” a century earlier in On the Origin of Species, writing that it made him doubt his own theory.
The paradox in question is the altruistic behavior exhibited most famously by social insects. Ants, termites, and some bees and wasps live in highly organized colonies in which most individuals are sterile or forgo reproduction, instead serving the select few who do lay eggs. Yet such behavior seemed to clearly violate the concept of natural selection and survival of the fittest, if “fittest” means the individual with the greatest reproductive success. The insects’ compulsory altruism — a form of extreme social behavior called eusociality — made little sense.
But that changed when Hamilton came up with his equation and formalized the theory known as kin selection . . .