  The Price equation provides a formal account of selection building on a
right-total mapping between two classes of individuals, that is usually
interpreted as a parent-offspring relation. This paper presents a new
formulation of the Price equation in terms of fuzzy set-mappings to account for
structures where the targets of selection may vary in the degree to which they
belong to the classes of "parents" or "offspring," and in the degree to which
these two classes of individuals are related. The fuzzy set formulation widens
the scope of the Price equation such that it equally applies to natural
selection, cultural selection, operant selection, or any combination of
different types of selection.
