In this article, Carl Woese provides a theory on the early evolution of cells. Woese posits that it is necessary to go beyond classic Darwinian thinking of Vertical Gene Transfer (parent to offspring). He believes that Horizontal Gene Transfer (HGT) played a more crucial role in the early development of cells; that is until each of the three branches of life (Bacteria, Archaea and Eucarya) reached their Darwinian Thresholds. This threshold is a point where the cells of random RNA and proteins have finally reached a level of complexity that they have become a “species” and Vertical Gene Transfer can take over. Before that, cells traded genetic material with each other, evolving as a community.
I commend Woese for attempting to push us past the thought of endosymbiosis. While endosymbiosis may have occurred, the two cells that combined had to have been fully evolved cells that functioned without each other before the joining. Careful consideration to his theory needs to be taken to understand how much of translation and transcription was evolved before bacteria, archaea, and eukaryotes emerged. The wide spread similarities and differences point to some truth in this.
Woese may have a better explanation than endosymbiosis as to how archaea, bacteria and eukaryotes evolved past their Darwinian threshold through HGT; however, he still cannot explain how those cells could initially evolve the genomes (albeit small) to trade parts with in the first place. He posits that translation existed before transcription or genome replication. RNA dominated and proteins were made, transcription completed evolution after each Darwinian threshold, and genome replication came third. I find it interesting yet hard to believe that nucleotides formed by themselves, without a metabolic pathway already in place, and in enough numbers to form RNAs capable of translating proteins. Enough amino acids would have to exist also and Woese gives no explanation for their appearance or the fact that they are conveniently in close proximity to the RNAs. I also find it hard to believe that such an incredible amount of nucleotides and amino acids existed to support enough primitive cells containing RNA and protein that were able to trade with each other, and that these ancient cells would survive long enough to reach a Darwinian threshold.
In conclusion, Carl Woese’s theory could have serious implications on our idea of the early evolution of cells when before we were content to recite “endosymbiosis” and leave it at that. However it still leaves us glaring at what we don’t know and may never know.
C. R. Woese (2002). On the evolution of cells Proceedings of the National Academy of Sciences, 99 (13), 8742-8747 DOI: 10.1073/pnas.132266999