Social evolution is a subdiscipline of evolutionary biology that is concerned with social behaviors that have fitness consequences for individuals other than the actor. Social behaviors can be categorized according to the fitness consequences they entail for the actor and recipient.

Mutually beneficial – a behavior that increases the direct fitness of both the actor and the recipient
Selfish – a behavior that increases the direct fitness of the actor, but the recipient suffers a loss
Altruistic – a behavior that increases the direct fitness of the recipient, but the actor suffers a loss
Spiteful – a behavior that decreases the direct fitness of both the actor and the recipient

This classification was proposed by W. D. Hamilton. He proposes that natural selection favors mutually beneficial or selfish behaviors. Hamilton's insight was to show how kin selection could explain altruism and spite.

Social evolution is also often regarded (especially, in the field of social anthropology) as evolution of social systems and structures.

In 2010, famed Harvard biologist E. O. Wilson, a founder of modern sociobiology, proposed a new theory of social evolution. He argued that the traditional approach of focusing on eusociality had limitations, which he illustrated primarily with examples from the insect world.

A parallel theory of progressive social evolution has been advanced by followers of Herbert Spencer (1820–1903). This theory rejects the conventional religious concept of human sin, which was based on the idea that, after the fall from grace, the human condition was eternally corrupt.