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View Diary: RIP Carl Woese: Evolutionary Pioneer (35 comments)

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  •  Of course no organism is easily .... (8+ / 0-)

    classifiable, based on the very core of evolutionary theory- i.e. no biological entity is static in space and time.  Add the mixing of genetic material, symbiotic relationships that are basic to the nucleated cell, epigenetic effects, and no organism can be said to be absolutely classifiable, least of all any "bacteria."

    Still we humans have trouble with the fact that the physical world cannot easily be characterized to fit our pre-conceived notions.  However, the species concept is useful, if we only keep in mind that it is not absolute truth, but only a human approximation of reality.

    •  Yes, but what is going on in procaryotes (6+ / 0-)

      is qualitatively different. IN eucaryotes, once a species has formed, it doesn't usually get new genetic material from outside. That is the whole point of the biological species concept, which is the predominant paradigm.

      Bacteria and (I think) Archeae pick up big chunks of DNA out of the environment, play around with it, and if it is useful it gets incorporated into their genome. They routinely transfer blocks of genes across phyla- like what happened to Jeff Goldblum in The Fly.

      Because of this, different strains of E. coli share less than half their genes- we are probably more closely related to strawberries than that. Some things, like genes for DNA, RNA, protein, and cell membrane synthesis, tend not to get moved around much. But genes for biochemical processes are readily transferred between the most distantly related bacteria. If you look at the phylogenetic distribution for a gene like a chemotaxis protein, it is scattered around like a drunk monkey was throwing darts at the tree.

      •  You are, of course, quite correct. (5+ / 0-)

        I was just pointing out that we can't even pinpoint multi-cellular categories with mathematical precision. In part this may be because of transfers by viruses of DNA from other species (See: for example.)  The species concept is, as you say, the predominant paradigm, but even not involving DNA transfers, it is difficult to define in some multicellular organisms.  Take our local whiptail lizards for example - how do you characterize a parthenogenic species?  Are some tapeworms, which self fertilize, species?

        •  I used to work on speciation in mosquitos (2+ / 0-)
          Recommended by:
          Desert Scientist, matching mole

          and other insects, so I understand what you are talking about. Things get squishy at the species level. But at higher levels- say above the family- things are pretty fixed in eucaryotes.

          That is not at all true in procaryotes. It isn't unusual for something to pick up half its genome from a totally unrelated source. That raises the question of what exactly "related" means in procaryotic evolution.

          •  To a large degree you are correct. (2+ / 0-)
            Recommended by:
            matching mole, Andrew F Cockburn

            The Culicidae, for example, is fairly stable as an entity, although the Chaoboridae was once included.  The Salticidae, a spider family on which I spent much of my career is also pretty stable,. especially since we added the Lyssomanidae (an artificial family since it was based on the eyes being in four rows and at least one subfamily of the Salticidae had about 3 and a half rows - I fail to see how the curve of eye rows are a "family" level characteristic when the enlargement of the anterior median eyes is a major derived character present in both "families.")

            However, the "Clubionoid" spiders have only recently been resolved into eight families, several of which are not even related to the rest. Some of these appear to be in the sister groups of the Salticidae and so I got involved in this.

            However, I fully recognize that this in not the same thing as what is occurring in procaryotes, but as eucaryotes are derived from procaryotes it does give one some pause as to how past evolutionary history might have been affected.

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