That conclusion was drawn too hastily; the aesthetic appeal of a dichotomy was too great. Simply because there are two types of cell at the microscopic level it does not follow that there must be only two types at the molecular level.
The evolutionary relation of prokaryotes and eukaryotes is actually more complicated than the evidence cited above would indicate. Two eukaryotic organelles, the mitochondrion and the chloroplast, each have their own DNA. Moreover, the pigments in the chloroplast (the chlorophylls and the carotenoids) are similar to those found in the cyanobacteria. Both mitochondria and chloroplasts are the size of bacteria; their apparatus for translating genetic information into proteins differs from the eukaryotic cell's own apparatus and has a number of properties in common with that of prokaryotes.
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Add CommentFascinating, fractal biology.
Reply | Report Abuse | Link to thisIt seems inevitable, in hindsight, that the more we seek to simplify the more complex things become.
I love when we prove our theories wrong, because it means we learned something new.
Kudos to all.
Why do we assume there was one common ancestor? The primordial soup existed all around the the world in various temperature, pressure, and atmospheric conditions. The best chemistry for that environment is the one that survived in that location. One for black smokers, one for lack of oxygen. The accumulation of oxygen in the atmosphere then drove the evolution of more advanced cells that could utilize the oxygen.
Reply | Report Abuse | Link to thisVoles (field mice) and Mice are two different species, seperately evolved, but difficult to distinquish.
Another interesting corollary of this research relates to the potential of finding archaeobacterial forms of life, either fossil or living, on Mars. Already microstructures reminiscent of methanobacteria have been discovered in meteorites of Martian origin. Recent orbital observations on Mars, and even some very recent Curiosity Rover samples indicate some methane emission from Mars. If we were to discover archaeobacteria on Mars, this would certainly up the ante for biological, and specifically genetic research, both on Earth and on the red planet.
Reply | Report Abuse | Link to thisWell done on a very good article on a very important area of research. It's this kind of article that reminds me of the "old" Sci-Am. Lets have more like this in 2013 please.
Reply | Report Abuse | Link to thisbefore the emergence of prokaryotes the pre ancisters of prokaryotes is their and why we are not discovering the first ancister of micro organisums. and at the earlier stage we discover three domains, their is a chance to discover more unknown domains in the world
Reply | Report Abuse | Link to thisNo, three lines of descent "that we know of". The arrogance; we knew there were two. We were wrong. Now we know there are three. We're probably still wrong.
Reply | Report Abuse | Link to thisThis is very interesting. I need to tell my biology teacher, if he/she is still teaching...
Reply | Report Abuse | Link to thisThroughout the text and image discussions, you continue to wrongly call the Archaea bacteria. The folly continues.
Reply | Report Abuse | Link to thisGreat article ... well written and thought provoking.
Reply | Report Abuse | Link to thisI am a retired geneticist and find the notion that one can begin to decipher the early evolution of life on this planet through the medium of the analysis of the nucleic acid sequences of extant pro/archae/eu/karyote genomes to be indeed fascinating.
With particular reference to the archeobacteria the implications for the discovery of life elsewhere in the solar system (and beyond) are compelling if not obvious.
Yes one and all great article. Really appreciate reading intelligent comments posted by science enthusiasts.
Reply | Report Abuse | Link to thisInteresting "diducthat" my main interest is and always has been the brain and all sciences as they relate. The reason I stopped subscribing to SA 30 years ago is that most articles were way over my head. I assume, at least for you, that SA "dumbed" down there rag to appeal more to my general level ... then of course, their brain related articles read too much like Psychology Today for my liking. Hey, you can please some of ...
I now have now subscribed to SA Brain. So I think SA is pleasing more of the people more of the time :)
I regret to inform you all that Professor Woese died on the 30th of December. He was a mentor for my current professor Dr. V who linked us this wonderful article. His intelligence will be missed but not forgotten as it has been passed down to his pupils.
Reply | Report Abuse | Link to thisRe: "The earth is four and a half billion years old, and on the basis of the macroscopic fossil record it would appear to have been inhabited for less than a seventh of that time: the entire evolutionary progression from the most ancient marine forms to man spans only 600 million years."
Reply | Report Abuse | Link to thisIt seems to me strange that the "most primitive" forms of life (seemingly found without ancestors) have such a long "evolutionary" history, while the "most complex" forms have a history so short in duration by comparison.
Peace to Prof. Woese. Yet, Biology cannot be defined via a language using terminology that has no definite relationship to ever expanding discrete energy/spaces as matter/time compresses due the origin of carbon signaling - emerging negative methyl groups as a function of a pyrimidine synthesis mechanism. Light operates through carbon. Oxygen molecule pulls up the strings of electron interfering systems of a negative carbon. At no oxygen spaces, protons via 'pumps' reduce carbon to its most compressible state -4 'running a perfect seasonal cycle'. Space is matter/antimatter occupying time determined by interference of particles/strings/waves. The likeliness of occupying space is taken upon the probability of localization as space/energy expansion occurs.
Reply | Report Abuse | Link to thisJust like in Physics, we assume there was one Big Bang that created the Universe. Why should we assume there was only one? I thought it was common sense to adopt developmental taxonomies, i.e., taxonomies that evolve with the developments in research. Only when we are sure that we now know everything can we come up with fixed categories, which is an impossibility as nature is not static.
Reply | Report Abuse | Link to thisSomebody, without research, simply decides that charge carriers in a solid conductor are positive, and so establishes the direction of an electrical current. When we discover that it is actually the electrons, which are negative, we go to a convention and come up we the "conventional current", thereby confusing many a high school pupil!
There is no need to be "conservative" in science. Let us allow the scientific body of knowledge to evolve freely, as we discard the inapplicable and incorporate the currently applicable. We enjoyed our Five Kingdom classification for some time. Now we have come across something we can't put even in a new kingdom. We are compelled to form higher divisions, domains. Let's do that. Textbooks can be rewritten.
This was/is a wonderful article, and a fantastic way to remember a great scientist and an equally great communicator. For a research microbiologist like me, much of this is, of course, "old hat", in that microbiology, evolutionary, biology, biochemistry, genetics, and molecular biology have been dealing with the implications of these discoveries for a number of years since the article was originally written. I have never read this article before, and was amazed at how forward thinking Dr. Woese was, how clearly he could postulate interpretations of the data that later became scientific dogma, and yet how clearly he could differentiate what could be inferred from the data and what could not. This is the true meaning of conservatism in science. In an era of whole genome sequencing, which Dr. Woese must have loved, 16S rRNA phylogenies are being replaces - somewhat - by whole genome phylogenies. Yet it is increasingly realized that, among bacteria at least, there are in some cases phylogenies of individual genes and that these are not always congruent at the level of the whole organism, even one as small and simple as the bacterium. The 16S phylogenies realized (made real, literally) by Dr. Woes and colleagues remain the foundation upon which newer data can be compared and organized. He was truly one of the giants upon whose shoulders the rest of us stand.
Reply | Report Abuse | Link to thisThe most interesting biological classification issues turn out not to be in finer and finer subdivisions but at the upper end of the scale. What's bigger than a kingdom? I would have said "empire" but biologists prefer "domain" or "superkingdom." So why did we miss this for so long? Because you need molecular biology and electron microscopes to see it. Linnaeus had no clue these organisms even existed.
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