 Supporters of an evolutionary account of function advertise the ease with which an account of malfunction follows from the theory as one of its virtues. Their idea is that we can say when a system is malfunctioning by observing that it is not carrying out the job which natural selection designed it to perform. In contrast, it is widely believed that systemic accounts of function cannot deal with malfunction at all. The argument goes like this: what a system is taken to do is relative to our explanatory interests, and that a putative malfunction can just be understood as a contribution to a different property of the system. Davies (2001) argues that the first of these claims can be defeated by restricting functional ascriptions to hierarchically organized systems in which lower level capacities realize upper level ones. That gives us a characterization of function independent of our explanatory interests.