1. Sober E. 1980. Evolution, population thinking and essentialism. Philos Sci. 47:360.
2. J. Gressel made this observation in an oral response after this paper was presented at the Weed Science Society of America meeting, February 1998.
3. McDaniel J. 1990. Where is the holy spirit anyway? Response to a skeptical environmentalist. Ecumenical Rev. 42(April): 165.
4. For essentialists, “… somewhere within the possible variations that a species is capable of, there is a privileged state—a state which has a special causal and explanatory role. The laws governing a species will specify this state … [but] the diversity of individual organisms is a veil which must be penetrated in the search for invariance.” [Sober, pp. 364–365] Modern biologists reject the natural state model because individuals within species have neither identical phenotypes nor genotypes. As Sober (1980) puts it, “… diversity itself constitute[S] an invariance, obeying its own laws.” [p. 365]