William Donald Hamilton (1936-2000)
Hamilton, who was an English professor and researcher, is perhaps one of the most significant evolutionary biologists of the 20th century. His greatest contribution was to formulate a rigorous genetic theory suggesting that altruism towards relatives and kin selection have a genetic origin. The impact of his theory was huge because it implies that morality has an evolutionary root, contrary to what humanity had always thought: that religion is the source of morality.
Kin selection is the selection of those characteristics that favor the survival of an individual’s close relative, with whom she shares her genome, even though it is costly to the individual. Without kin selection, it is hard to explain why an individual would help another without receiving anything in return, just as parents do for their children. Altruism also helps explain why individuals sacrifice themselves for others, why they help their loved ones, and why they do and return favors.