Rational taxonomy and the natural system

Since Darwin's theory of evolution by natural selection, the idea of descent with modification came to dominate systematics, and so the study of morphology became subgugated to the reconstruction of phylogenies. Reinstating the organism in the theory of evolution (Ho & Saunders, 1979; Webster & Goodwin, 1982) leads to a project inrational taxonomy (Ho, 1986, 1988a), which attempts to classify biological forms on the basis of transformations on a given dynamical structure. Does rational taxonomy correspond to thenatural system that Linnaeus and his contemporaries as well as all pre-Darwinian morphologists had in mind? Here, we examine how rational taxonomy and the natural system can coincide in the dynamics of processes generating forms during development, which conferexclusivity, genericity androbustness to the forms that do exist. We use the example of segmentation, especially inDrosophila, as an illustration to explore the implications of rational taxonomy for evolution and systematics, and the relationship between ontogeny and phylogeny.