Each provides functional advantages and thus favored in evolutionary development.
Yet human behavior is not determined solely by a fixed genome.

It shapes instincts in each member that are fundamentally selfish with reference to other members.
In contrast, group selection consists of competition between societies, through both direct conflict and differential competence in exploiting the environment.

Individual selection is the result of competition for survival and reproduction among members of the same group.

Both traits appear to have evolutionary advantages, selfishness for survival of an individual within a group, and altruism for the cohesiveness and survival of the group.

During interpersonal conflicts such differences can be highly consequential, with some individuals more likely to wage conflicts more competitively, others to wage them more collaboratively, and others to avoid conflicts altogether.