The behaviour of human social groups can be studied by applying models from e.g. sociology and economics, but it can also be studied by applying models from evolutionary biology. One question concerning the former models is the question of methodological individualism: roughly, the extent to which causal explanation of the behaviour of social groups can/should take place "in terms of individuals" (Watkins 1957, Lukes 1968, Kincaid 1996 1997). One question concerning the latter models is the question of group selection explanations. Can the phenotypes of biological groups or biological individuals be explained by appealing to what is good for the group? (Maynard-Smith 1964, Sterelny 1996, Sober and Wilson 1998, Okasha 2006, Lehmann et al 2007). This question is arguably of great importance to the study of cultural evolution (Boyd and Richerson 1998).

As a result there has been much discussion of how the issue of methodological individualism as regards social science relates to the issue of group selection as regards evolutionary biology. (In particular the articles collected in Koppl's "Evolutionary Psychology and Economic Theory", 2004.) Are the two compatible? I take this question to amount to the following: can one explain the behaviour of human social groups (a) only "in individual terms" and (b) by appeal to what is good for the group?

There seems to be a growing consensus that the answer to this question is "yes". I agree. I argue, however, that there is much more to the relationship between GS and MI than this alone acknowledges. In particular, I say, that to fully embrace the ethos behind MI requires taking a very particular position in the philosophical debate over the status of group selection. Namely:

(a) group selection is a causal process

(b) this causal process is distinct from the process of kin selection

(c) so group selection and kin selection models are not interchangeable

(d) none of the present measures of the strength of within-group vs between-group selection are universally applicable. nor could they be.

(e) thinking of group selection in terms of levels of nature is, at best, misleading