 An evolutionary approach faces problems in specifying what the overall evolved function of a system might be and showing how functions contribute to it. First, it is very difficult to assess the relevant evidence that a given biological systems is — as in Wakefield’s treatment — the product of natural selection (Davies 2001, Chapter 5). Since many ailments do not prevent one from living and having children, it is even harder to show that a disease is necessarily the product of a malfunction that lowers fitness or — as in Boorse — interferes with survival and reproduction. Another problem for Wakefield is that if you regard evolutionary dysfunction as partly constitutive of disease then if an illness depends on structures that have no evolved function, it cannot really be an illness. A biological structure might be a spandrel or a by-product, or have some other non-selective history. Such a structure cannot malfunction in Wakefield’s sense, and so it cannot be diseased in the primary, evolutionary sense.The idea would have to be weakened to suggest that it is diseased in a derivative sense in virtue of its implications for other selected effects elsewhere in the system 