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Two or three primary domains?

  1. Dec 10, 2016 #1
    I'm wondering if the issue of bacteria and archaea having a single last universal common ancestor (LUCA) with eukarya diverging later, or all three having distinct common ancestors, has been clarified. I've seen a number of texts indicating the eukarya diverged much later, but also some indicating much earlier origin of eukarya.


    Last edited: Dec 10, 2016
  2. jcsd
  3. Dec 11, 2016 #2


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    The current picture for the evolution of eukaroytes is that they arose from a fusion between an archaeon and a bacterium (which would give rise to mitochondria) through a process called endosymbiosis. Previously there had been some debate whether the host before fusion occurred was a geniune archaeon or a species outside of archaea, but most evidence points to eukaryotes having arisen from within archaea. Therefore, the two domain model is probably most correct though many textbooks still teach the three domain model (which treats us as eukaryotes as our own special domain rather than some subset of domain archaea).

    For more discussion see these previous PF threads on the topic as well as the papers they reference:
    Are there really three domains of life? discusses a nice review article on the topic
    Lokiarchaeota and the Evolution of Complex Cellular Life discusses a paper identifying a new species of archaea that is likely very similar to the one that gave rise to eukarya.
    A Ring of Life and When did Miotochondria Evolve? discuss the evolution of eukaryotes and endosymbiosis.
  4. Dec 11, 2016 #3
    Thanks. That was my belief, but I had come across articles supporting the 3 domain model. Some state that eukarya originated 2.8 billion years ago, but that seems to be based on a misinterpretation (or contamination) of evidence.
  5. Dec 11, 2016 #4


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    Well, that is very interesting @Ygggdrasil.
    I was no longer upto date on this stuff.

    By the way, I found a free access version of this article:

    It seems no one has identified these cells yet though.
    Too bad!
  6. Dec 11, 2016 #5


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    Hopefully someone is working on this. Of course, culturing microbes in the laboratory can be quite tricky, so it may take a while before someone is successful.
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