Altruism and organism: disentangling the themes of multilevel selection theory.

The evolution of groups into adaptive units, similar to single organisms in the coordination of their parts, is one major theme of multilevel selection theory. Another major theme is the evolution of altruistic behaviors that benefit others at the expense of self. These themes are often assumed to be strongly linked, such that altruism is required for group-level adaptation. Multilevel selection theory reveals a more complex relationship between the themes of altruism and organism. Adaptation at every level of the biological hierarchy requires a corresponding process of natural selection, which includes the fundamental ingredients of phenotypic variation, heritability, and fitness consequences. These ingredients can exist for many kinds of groups and do not require the extreme genetic variation among groups that is usually associated with the evolution of altruism. Thus, it is reasonable to expect higher-level units to evolve into adaptive units with respect to specific traits, even when their members are not genealogically related and do not behave in ways that are obviously altruistic. As one example, the concept of a group mind, which has been well documented in the social insects, may be applicable to other species.