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As I vaguely understand it, both combination and separation have played important roles in evolution. Combination, for example, in that the nuclei, mitochondria
by mirimir 7y ago
As I vaguely understand it, both combination and separation have played important roles in evolution. Combination, for example, in that the nuclei, mitochondria and chloroplasts of modern eukaryotes derive from initially separate organisms.
Many eukaryotes carry transposable elements, which are DNA sequences that exploit DNA and RNA machinery to create numerous copies of themselves in the genome. That is, they're like viruses, except that for the most part they don't get transmitted, except through cell replication.
But I believe that there are examples where transposable elements do get transmitted like viruses. Or sometimes as parasites on actual viruses. So that's separation. And there are also examples, where viruses become integrated into the genome. Sometimes reversibly, as with HSV, which is why you can never really cure an HSV infection.
Anyway, it seems most likely that simple stuff evolved first, and then combined into more complicated stuff. But the simple stuff has survived, to some extent, as transposable elements and viruses.
- chongli 7y agoYes, although they are relatively simple compared to other organisms, viruses are still extremely complex when compared to the simple organic compounds you'd expect to form spontaneously in a pre-biotic world. That is what makes all the difference. It's an enormous leap to go from a couple of amino acids to something able to survive and evolve and compete against other complex organisms.
- mirimir 7y agoYes, agreed. It is possible, I suppose, that remnants of other "starts" could have survived somewhere that's totally inhospitable to ours. Or perhaps, so different that they're not even food. Discovering them would be very difficult, though. I mean, we have a hard enough time with all those "unculturable" bacteria. We only know them now through DNA technology.
- TeMPOraL 7y agoI recently learned from "The Vital Question" that lateral gene transfer is not just a thing that occasionally happens, but something bacteria do all the time by default. Anyway, I think we're still talking an order or two of magnitude difference between DNA/RNA (and supporting infrastructure) and the point at which proto life 2.0 transitions from "background chemistry" to "bacteria food". I've so far read in detail about only one hypothesis on abiogenesis (in aforementioned book), and there the necessary environmental conditions were since changed by very existence of life.
- mirimir 7y agoI was trying to generalize from what we know about lateral gene transfer, and the history of mitochondria and chloroplasts, to the transition from proto life to life. Something like "proto life A" and "proto life B" get incorporated into "proto life C" to make "proto life D". And after enough steps like that, you get life. In a sense, that's a trivial statement. Because that's just what chemistry is about. Or deeper, just what physics is about. But regarding GP's point, I'm saying that it's too simplistic to argue about whether life originated once or multiple times. Maybe there were multiple beginnings, which combined and interacted in multiple ways. As we know now for evolution from primate-like ancestors to modern humans. The machinery of DNA and RNA is one example. It's a chunk that worked. Or maybe multiple chunks that got combined. And the same with ATP synthase and the flagella motor.