 This combined requirement of engineering group-level adaptation in addition to the existence of an interactor at the group level is a very popular version of the necessary conditions for being a unit of selection within the group selection debates. For example, it was claimed that the group selection issue hinges on “whether entities more inclusive than organisms exhibit adaptations” (Hull 1980: 325). Another view states that the unit of selection is determined by “Who or what is best understood as the possessor and beneficiary of the trait” (Cassidy 1978: 582). Similarly, paleontological approaches required adaptations for an entity to count as a unit of selection (Eldredge 1985: 108; Vrba 1983, 1984).