 Because this disposition was both limited and unstable, however, and competed with powerful selfish drives, there was a continual threat of social rupture and loss of cooperative advantage. This in turn would have made ongoing peacemaking a necessity, thus limiting the size of viable cooperative units and the scope of cooperative projects, as well as imposing significant costs through the devotion of time and energy to peacemaking activities. An example would be extensive mutual grooming going well beyond what is necessary for hygiene, of the sort found in chimpanzee societies.