Reeve and Holldobler put forward a theory of a superorganism. They look at competition and co-operation "between" groups as well as "within" groups. In their model, an individual's inclusive fitness varies according to how much it invests in within-group competition (e.g. hoarding a private food cache) versus between-group competition (e.g. contributing to common foraging); and on its relatedness to the other group members.