The XVIIIth (New) International Congress of Zoology

Le XVIIIème (Nouveau) Congrès International de Zoologie

At the turn of the century, when knowledge was sparse compared with the present, there was much hope that protozoan and metazoan phylogeny could be unravelled by increased research and the discovery of new taxa. In the seventies, cladists were convinced that their method could provide a stable system for all organisms. Finally, in the eighties and nineties, molecular biologists were full of hope that they had the "universal tree of life" at the turn of the millennium. Unfortunately, all claims and hopes were blurred by the "brush phenomenon". Briefly, the phenomenon runs as follows: As long as knowledge is sparse, taxa are separated by very distinct gaps and thus represent highly characteristic evolutionary lines. As knowledge increases, that is, some or many of the less "typical" taxa are included in the analysis, the distinctiveness of the evolutionary pathways decreases more and more and incongruences increase. Finally, the data do not produce a "tree" but a more or less distinct "bush" or "brush". Impressive examples are the papers by Cavalier-Smith (1998, Biol. Rev. 73: 203-266) on protists and by Ehab Abouheif et al. (1998, J. Mol. Evol. 47: 394-405) on multicellular organisms. The brush phenomenon is scale-independent, that is, it can be observed between phyla as well as families and genera. Accordingly, common mechanisms appear likely. I suggest that these mechanisms correspond to parallel and convergent evolution, both of which are likely to be much more common than presently recognized. The more taxa are analyzed, the more unrecognized convergences accumulate and disturb the tree, especially in molecular systematics, where plesiomorphies and apomorphies cannot yet be distinguished. There is little hope that the problems can be solved by any method in the near future. New ways of thinking and working are necessary. For instance, algorithms which combine classical morphological and modern molecular data should be developed and more micropaleontological data should be collected. Likewise, a more intensive collaboration between morphologists and molecular biologists is necessary. Thus, both fields, molecular biology and morphology need equal support by federal governments and grant institutions.