The target article contains a number of distinct but interrelated claims about the cognitive nature of folk biology based in part on cross-cultural work with urbanized Americans and forest-dwelling Maya Indians. Folk biology consists universally of a ranked taxonomy centered on essence-based generic species. This taxonomy is domain-specific, perhaps an innately determined evolutionary adaptation. Folk biology also plays a special role in cultural evolution in general, and in the development of Western biological science in particular. Even in our culture, however, it retains an autonomy from other domains of thought and from science. These claims are questioned and clarified.

Differences of opinion between Epstein, Flynn & Martohardjono (1996) and some commentators can be traced to different interpretations of Universal Grammar (UG) form or strategy. Potential full access to the form of linguistic universals in second language acquisition may be distinguished from access to UG strategy, but Epstein et al.'s dismissal of the Critical Age Hypothesis clouds their central argument.

Universal Grammar (UG) can be interpreted as a constraint on the form of possible grammars (hypothesis space) or as a constraint on acquisition strategies (selection procedures). In this response to Herschensohn we reiterate the position outlined in Epstein et al. (1996a, r), that in the evaluation of L2 acquisition as a UG- constrained process the former (possible grammars/ knowledge states) is critical, not the latter. Selection procedures, on the other hand, are important in that they may have a bearing on development in language acquisition. We raise the possibility that differences in first and second language acquisition pertaining to both attainment of the end-state and course of development may derive from differences in selection procedures. We further suggest that for these reasons age effects in the attainment of nativelike proficiency must necessarily be separated from UG effects.