This article is primarily a study of the group selection controversy, with special emphasis on the period from 1962 to the present, and the rise of inclusive fitness theory. Interest is focused on the relations between individual fitness theory and other fitness theories and on the methodological imperatives used in the controversy over the status of these theories. An appendix formalizes the notion of "assertive part" which is used in the informal discussion of the methodological imperatives elicited from the controversy.

The question "what is (are) the unit(s) of selection" can be interpreted in three different ways. These interpretations are discussed and it is shown that they prompt different answers; such units are shown to be individuals in the context of the given interpretation. One of these interpretations is argued, by examples, not always to have an unambiguously correct answer. An alternative approach to this question is sketched.