Social interaction types are classified by fitness costs and benefits to actor and recipient.

Evidence

Hamilton (1964a; 1964b) famously classified forms of social interaction between an “actor” and a “recipient” according to whether the consequences they entail for actor and recipient are beneficial or costly (with benefits and costs measured in terms of direct fitness). He called behavior that is beneficial to the actor and costly to the recipient (+/−) selfishness, behavior that is costly to the actor and beneficial to the recipient (−/+) altruism, and behavior that is costly to the actor and costly to the recipient (−/−) spite. Following a number of authors (Clutton-Brock 2002; Emlen 1997; Gardner & West 2004; Krebs & Davies 1993; Ratnieks 2006; Tomasello et al. submitted), we call behavior that is beneficial to both the actor and the recipient (+/+) mutualism. Cooperation is social behavior that is beneficial to the recipient, and hence cooperation can be altruistic or mutualistic. — Nicolas Baumard, A mutualistic approach to morality, 13

Categorization

• DEFINE: Clean taxonomy of selfishness, altruism, spite, and mutualism by fitness effects — useful reference framework.