Taxon: Is It Taxonic? 1 Taxon: Is It Taxonic?

Taxometric method, invented by Paul Meehl (1965) and developed by him and a number of colleagues, is a family of procedure for subjecting parts of a certain class of theories to risky tests. The theories in question postulate the existence of a latent category, the taxon, and its complement class. A taxon is negatively defined as a " non-arbitrary latent category. " It does not appear to be possible to positively and precisely define " taxon " (Meehl, 1999, p. 197). In fact, this appears to be because " taxon " is an open concept (Pap, 1953), for one reason because the list of its exemplars is indefinitely extensible. Nevertheless, examples of clearly taxonic categories are easy to find in biology, medicine, and even sociology: biological species; biological sex (at least for species where sex is determined chromo-somally); Huntington disease, phenylketonuria and other completely penetrant, single-gene disorders; and being a member of certain discrete, often isolated or especially tightly-knit, A complement class, on the other hand, may or may not be particularly cohesive, discrete, or isolated. While smallpox sufferers constitute a taxon, the class of individuals who do not have smallpox is not. On the other hand, the classes of male and female persons both constitute taxa, which (excluding rare phenomena, i.e., hermaphrodites and chromosomal aneuploidies) exclusively and exhaustively partition the human race. The reader should note particularly that " taxon " is a term referring to certain causal structures , which are the reason why the class in question is phenotypically discrete, or the social group is isolated. It is not merely a way of referring to statistical properties of distributions of manifest variables, in respect of the latent class, as is done with finite mixture