Worker policing in the wasp Dolichovespula saxonica . Classic examples of altruism occur in the social insects, where workers forgo their own reproduction to raise the queen's offspring. Hamilton's inclusive fitness theory (also referred to as kin selection theory) showed that individuals might give up their personal fitness if it enhances that of their relatives (Box 1) [12, 13]. Nevertheless, additional mechanisms can also be important for enforcing cooperation and preventing selfish behaviors [1, 7, 8, 70]. Here, a worker that lays an egg (left) has that egg eaten by another worker (right). Photo courtesy of Kevin Foster, Harvard University.