RATIONAL TAXONOMY AND THE NATURAL SYSTEM

Since Darwin's theory of evolution by natural selection, the idea of d escent with modification came to dominate systematics, and so the stud y of morphology became subjugated to the reconstruction of phylogenies . Reinstating the organism in the theory of evolution (Ho & Saunders, 1979; Webster & Goodwin, 1982) leads to a project in rational taxonomy (Ho, 1986, 1988a), which attempts to classify biological forms on the basis of transformations on a given dynamical structure. Does rationa l taxonomy correspond to the natural system that Linnaeus and his cont emporaries as well as all pre-Danwinian morphologists had in mind? Her e, we examine how rational taxonomy and the natural system can coincid e in the dynamics of processes generating forms during development, wh ich confer exclusivity, genericity and robustness to the forms that do exist. We use the example of segmentation, especially in Drosophila, as an illustration to explore the implications of rational taxonomy fo r evolution and systematics, and the relationship between ontogeny and phylogeny.