Problems with “Procaryote”

Abstract

The procaryote-eucaryote model, as is explicit in the language, posits that fundamentally there are two kinds of organisms, procaryotes and eucaryotes. Furthermore, the prefix “pro” injects the connotation that procaryotes preceded eucaryotes because “pro” means before. This procaryote-eucaryote model dominates our textbooks and discourse in matters of taxonomy and deep evolution. The thesis of this article is that the notion of procaryote is now obsolete and counterproductive. Here, I (i) trace the source of the procaryote-eucaryote model, (ii) show why it is wrong scientifically, and (iii) comment on the damage it has done to our perception of important biological issues. I conclude that “procaryote” needs to be retired from the lexicon of biology. THE ESSENCE OF THE ARGUMENT The procaryote-eucaryote concept was a specific hypothesis, and it has been proven wrong by 3 decades of results in molecular phylogeny and biochemistry. These results, summarized below, show that life’s diversity falls into three fundamentally distinct phylogenetic domains: Bacteria, Eucarya (eucaryotes), and Archaea. Moreover, the results show that archaea and eucaryotes evolved independently of the bacterial line of descent. Thus, there is no such thing as a “procaryotic” relatedness group of organisms in any phylogenetically based taxonomy. It makes no sense to lump bacteria with archaea phylogenetically. Furthermore, the molecular tree reveals no group of organisms that preceded eucaryotes. The accompanying diagrams contrast the procaryote-eucaryote and three-domain models for the large scale of biological organization and the course of evolution.