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There's nothing here that really shows that "life began not just once but at least twice on Earth." Just because they have different metabolism (even dramatica

There's nothing here that really shows that "life began not just once but at least twice on Earth." Just because they have different metabolism (even dramatically different) it doesn't exclude the possibility that life began once and then branched (via evolution) into these two groups that derive their energy from different elements. After all, sulfur-reducing bacteria (which use sulfur instead of oxygen) are well-known and nobody suggests independent origins for them.

michaelfeathers 16y ago
That makes me wonder if there are any "you can't get there from here"s in biology.. metabolic bases that are so different that they could not have been progenitors of each other through evolution. I suppose the answer is probabilistic.
- tome 16y ago
  This is what "intelligent design" proponents are trying to prove all the time, isn't it?
  - michaelfeathers 16y ago
    True, but if found a striking example of "you can't get there from here" would marginalize their efforts.
- roadnottaken 16y ago
  Well, as gort pointed out, if they adhere to the central dogma (DNA > RNA > Protein) then the answer is 'probably not' (i.e. you can get everywhere from there). However, if they used an entirely different type of chemistry to make life then I think it would be likely that they evolved separately.
eliben 16y ago
Doesn't it depend on just how different these organisms are? If, for example, they have nothing resembling the cell of a prokaryotic or eukaryotic organisms (DNA, etc.), it can definitely mean something big. If they have the same "conceptual" cell but the details of its internals differ somewhat, then indeed it's far from scandalous, it just means the evolutionary tree branched earlier than with other organisms. The second case would also be interesting in itself, of course.
kashif 16y ago
Being pedantic here... (via evolution) Evolution is not a process, it is an effect. Evolution does not cause things to happen. Genetic mutation is the reason life evolved. Just had to say that.
- Dylan16807 16y ago
  It's not a cause, sure. But I have never heard the word evolution defined to not apply to the process. Do you have a better reference I could read?
jerf 16y ago
Evolutionary processes aren't magic, they can only move along gradients defined by small changes. If it can be shown that these bacteria have something so radically different that it couldn't possibly have gotten there by small changes, such as by having a biology with no resemblance to DNA/RNA as we know it, then I'll have to accept a second origin. However, if these things were just discovered I find it unlikely these have been analyzed to the point that we can be conclusive about it. Historically speaking people have tended to get radically more excited about this sort of thing than they have scientific justification for, for a variety of reasons. The full answer will probably take longer, unless they've been successfully sitting on this for a rather long time. A slow process of swapping in arsenic for phosphorus might cover it and leave something superficially distinct from modern life but still clearly descended from it.

michaelfeathers 16y ago

That makes me wonder if there are any "you can't get there from here"s in biology.. metabolic bases that are so different that they could not have been progenitors of each other through evolution. I suppose the answer is probabilistic.

tome 16y ago
This is what "intelligent design" proponents are trying to prove all the time, isn't it?
- michaelfeathers 16y ago
  True, but if found a striking example of "you can't get there from here" would marginalize their efforts.
roadnottaken 16y ago
Well, as gort pointed out, if they adhere to the central dogma (DNA > RNA > Protein) then the answer is 'probably not' (i.e. you can get everywhere from there). However, if they used an entirely different type of chemistry to make life then I think it would be likely that they evolved separately.

eliben 16y ago

Doesn't it depend on just how different these organisms are? If, for example, they have nothing resembling the cell of a prokaryotic or eukaryotic organisms (DNA, etc.), it can definitely mean something big. If they have the same "conceptual" cell but the details of its internals differ somewhat, then indeed it's far from scandalous, it just means the evolutionary tree branched earlier than with other organisms. The second case would also be interesting in itself, of course.

kashif 16y ago

Being pedantic here... (via evolution) Evolution is not a process, it is an effect. Evolution does not cause things to happen. Genetic mutation is the reason life evolved. Just had to say that.

Dylan16807 16y ago
It's not a cause, sure. But I have never heard the word evolution defined to not apply to the process. Do you have a better reference I could read?

jerf 16y ago

Evolutionary processes aren't magic, they can only move along gradients defined by small changes. If it can be shown that these bacteria have something so radically different that it couldn't possibly have gotten there by small changes, such as by having a biology with no resemblance to DNA/RNA as we know it, then I'll have to accept a second origin. However, if these things were just discovered I find it unlikely these have been analyzed to the point that we can be conclusive about it. Historically speaking people have tended to get radically more excited about this sort of thing than they have scientific justification for, for a variety of reasons. The full answer will probably take longer, unless they've been successfully sitting on this for a rather long time. A slow process of swapping in arsenic for phosphorus might cover it and leave something superficially distinct from modern life but still clearly descended from it.