The upshot of our excursions into the contemporary history of ideas in Part II of this book was that the post-Hempel development of the study of functional explanation has come a significant step forward by introducing an explicit feedback provision. I have taken this as the feature common to all positions labeled as etiological. This has, however, gone hand in hand with a loss of generality of the analysis because later analysts have tended to identify this feedback mechanism either with natural selection or with human intentionality and thus can only cope with the functions of artifacts and organic traits; within biology, they deal only with evolutionary questions. Later literature generally denies functions to evolutionarily new organic traits – although neither Hempel nor Nagel was forced to take this position. Physiological, as opposed to evolutionary, functions are not dealt with as such, and the analysis of social functions has generally been dropped altogether. Furthermore, most recent literature oriented toward biology has discarded Hempel's welfare provision. And none of it has, to my knowledge, taken up the analysis of the two-part instrumental relation of relative and intrinsic purposiveness that we saw in both Hempel and Nagel.

The dispositional view in its various forms has retained as essential the relation to a containing or reference system, but it doesn't view functions as explanatory in a causal sense. The etiological view retains the relation to a system only in those versions devoted to the philosophy of special sciences, either biology or sociology.