This refers to a biological rule that determines when an animal will engage in altruistic behaviour that seemingly does not improve its own well-being. Hamilton’s rule, named after the English evolutionary biologist W.D. Hamilton, states that an animal will engage in altruistic behaviour only when the indirect benefits that it derives from such behaviour are greater than the direct reproductive cost that it incurs. When an animal shares common genes with another animal that is in need of help, for instance, it is likely to exhibit altruism. This has led many biologists to believe that altruism could simply be selfish behaviour at the gene level.