 The kinds of reasons that may be advanced could either be internal to, or independent of the biological sciences. If the former, then various theoretical options may seem viable. The first grounds in the claim that, although species are not natural kinds and are thus unsuited to figuring in laws of nature (Hull 1987: 171), they do support descriptions with a significant degree of generality, some of which may be important (Hull 1984: 19). A theory of human nature developed on this basis should explain the kind of importance on the basis of which particular properties are emphasised. The second theoretical option is pluralism about the metaphysics of species: in spite of the fairly broad consensus that species are defined as units of evolution, the pluralist can deny the primacy of evolutionary dynamics, arguing that other epistemic aims allow the ecologist, the systematist or the ethologist to work with an equally legitimate concept of species that is not, or not exclusively genealogical (cf. Hull 1984: 36; Kitcher 1986: 320ff.; Hull 1987: 178–81; Dupré 1993: 43f.). The third option involves a relaxation of the concept of natural kinds, such that it no longer entails the instantiation of intrinsic, necessary, sufficient and spatiotemporally unrestricted properties, but is nevertheless able to support causal explanations. Such accounts aim to reunite taxonomic and explanatory criteria, thus allowing species taxa to count as natural kinds after all (Boyd 1999a; R. Wilson, Barker, &amp; Brigandt 2007: 196ff.). Where, finally, the reasons advanced for privileging certain properties are independent of biology, these tend to concern features of humans’—“our”—self-understanding as participants in, rather than observers of, a particular form of life. These are likely to be connected to normative considerations. Here again, it seems that a special explanation will be required for why these privileged properties should be grouped under the rubric “human nature”.