Ontogénie, phylogénie et homologie: Les tests de l'hétérochronie

Abstract

Paedomorphosis, or its generating processes neotenyand progenesis, obscures considerably phylogenetic patterns since it is an apparent falsifier of ontogeny, which is regarded as an a priori, direct argument in character analysis. How to discover this type of heterochrony, which results in terminal deletions, is a particular problem, since it consists of searching for absent characteristics, thus characteristics the homology of which is not refutable. However, if heterochronies, and neoteny or progenesis in particular, are relevant to any theory of evolutionary process, they have to be discovered by some means, that is, there must be a technique to make them refutable. Terminal deletions of particular characteristics in the development of an organism are refutable on the basis of parsimony, in the frame of a phylogeny reconstructed by the usual cladistic techniques (ontogeny, out-group comparison, paleontology). Neoteny is thus assumed when convergence (on other characteristics) is not parsimonious. By contrast, general neoteny or progenesis, that is, phylogenetic reversion, is not refutable, hence not knowable, through ontogeny and out-group comparison, because it is beyond the bounds of parsimony. therefore, such a case is hardly known in neontology. Paleontology may be one way to refute a hypothesis of general neoteny, despite the incompleteness of fossils, but it rather generates this type of hypothesis. The most reliable way of refuting general neoteny, progenesis or paedomorphosis may be analytic biogeography. This difficulty to evaluate the refutability of a relatively simple developmental heterochrony should be taken into consideration when heterochronies or their combinations are given a major explanatory power in evolutionary processes.