The concept of adaptation is pivotal to modern evolutionary thinking, but it has long been the subject of controversy, especially in respect of the relative roles of selection versus constraints in explaining the traits of organisms. This paper tackles a different problem for the concept of adaptation: its interpretation in light of multilevel selection theory. In particular, I arbitrate a dispute that has broken out between the proponents of rival perspectives on multilevel adaptations.
Many experts now say that multilevel and kin selection views are mathematically equivalent to one another—that the mathematical accounting of evolution can be carried out at any hierarchical level one chooses. But what does this formal equivalence imply - are they equivalent in other ways too? I show here that significant conceptual non-equivalence has survived: the two sides commit to different views regarding how much selection has to act at a level before we can call traits at that level adaptations; about whether policing mechanisms are adaptations, and about whether non-organisms can bear adaptations.