 To avoid such implications, Samuels shores up his proposal with a proviso: a psychological structure is innate just in case it is psychologically primitive and it would develop under normal conditions for a member of the species. This move has prompted some philosophers to generate further counterexamples of acquired traits that are psychologically unexplainable but nonetheless emerge under “normal” conditions (e.g. Khalidi 2007). A deeper question, however, concerns the very notion of a “normal” developmental environment. Spelling out this idea is no easy matter. Presumably, a necessary condition for some environment to qualify as normal for a species is that it was encountered ancestrally. But this raises the twin problems of how far back in time is relevant, and how can we classify environments as types. Samuels argues that these problems plague any discipline that appeals to the notion of a normal environment and are thus not unique to psychology. However, it remains an open question whether the concept of normal environment can made coherent. We return to this issue in Section 3.4 (below).