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 e