Ontogeny–a way forward for systematics, a way backward for phylogeny

In the history of biology, the term 'evolution' has carried a dual meaning, viz. ontogeny (the unfolding of the germ) versus phylogeny (descent with modification). A problem in modern biology is the question of whether it is ontogeny which creates phylogeny, or whether it is phylogeny which moulds ontogeny. The paper explores the relationship of ontogeny to phylogeny in the context of 'pattern cladism'. The conclusion is that the analysis of ontogeny provides a direct method for classification ('a way forward for systematics'), which is a logical prerequisite for a phylogenetic interpretation of ontogenetic sequences ('a way backward for phylogeny'). The ontogenetic process of growth, subdivision and differentiation is related to the 'morphogenetic tree theory' on the basis of Von Baer's "laws of individual development". This conceptual relation shows that ontogeny creates phylogeny in an upward direction within the morphogenetic tree, whereas phylogeny (by means of natural selection) moulds ontogeny in a downward direction. A conflict originates with the conventions of Linnaean classification if ontogenetic divergence is proposed as a causal agent in the origin of higher taxa. It is proposed to solve this conflict by viewing individual organisms (or reproductive communities) not as constituents, but as representatives of higher taxa.