I've prepared a bunch of exam questions for students in my molecular evolution course. I gave them out two weeks before the exam and I promised them that I would post some of these questions on my blog to see how you would answer them. I'm hoping that you, dear readers, will show my students that there really is some controversy.
Here's the fourth question.
Norman Pace (2006) says,My students have a copy of the Nature article and we've also discussed the Three Domain Hypothesis. You can learn about some of the controversy at The Three Domain Hypothesis.I believe it is critical to shake loose from the prokaryote/eukaryote concept. It is outdated, a guesswork solution to an articulation of biological diversity and an incorrect model for the course of evolution. Because it has long been used by all texts of biology, it is hard to stop using the word, prokaryote. But the next time you are inclined to do so, think what you teach your students: a wrong idea.Outline the main reasons why Pace wants to ban the word “prokaryote.” Do you agree with him?
Norman Pace is currently Distinguished Professor of Molecular, Cellular and Developmental Biology at the University of Colorado, Boulder.
Part of this discussion is about taxonomy and the proper way to classify organisms. We didn't talk about that in class but for completeness here's what Ernst Mayr has to say about Pace's idea (Mayr, 1998).
In contrast to a Hennigian cladification, the Darwinian classification uses two sets of criteria. Although all taxa must be monophyletic, that is, descended from the nearest common ancestor, they are ranked according to the degree of difference from each other. Therefore, one must ask, are the archaebacteria as different from the eubacteria as from the eukaryotes or are they much more similar to the eubacteria, thus justifying the inclusion of both kinds of bacteria in the prokaryotes and confirming the two-empire classification?
Mayr, E. (1999) Two empires or three? Proc. Natl. Acad. Sci. (USA) 95:9720-0723. [PNAS Free PDF]
Pace, N.R. (2009) Time for a change. Nature 441:289. [doi:10.1038/441289a]