4 ms·

ANY examples of life simpler than a bacterium Viruses are much simpler, for one. Or perhaps you don't consider them to be life forms. Either way, if you unders

ANY examples of life simpler than a bacterium Viruses are much simpler, for one. Or perhaps you don't consider them to be life forms. Either way, if you understand how bacteria operate at even the most crude level, you'll realize that they (all bacteria, collectively; individually, they're specialized, of course) eat basically anything and everything in terms of organic molecules. What are the ramifications for this? It means any sort of abiogenesis that takes place today needs to somehow avoid being immediately eaten by bacteria and then continue to survive for potentially millions of years in order to evolve into an advanced life form. Needless to say, this seems to be vanishingly unlikely these days.

garmaine 7y ago
Viruses are life, but they depend on the machinery of other, more complex life to reproduce. Life doesn't start with viruses, for if it did, how would they reproduce?
- chongli 7y ago
  You asked about examples of life simpler than bacteria. You didn't stipulate that they had to be ancestors. How would that even work, anyway? An organism would have to be extremely long-lived to be living concurrently with its direct, more complicated descendent.
  - TeMPOraL 7y ago
    > How would that even work, anyway? Think in terms of lines, not individuals. Mutations are acquired on individual level, so out of a whole family of bacteria, one individual may reproduce into something slightly different, while the rest of the family continue unchanged. (Modulo fast mutation rate in bacteria, and modulo the wide use of horizontal gene transfer. The more I learn about bacteria and archaea, the more I feel there's little point in trying to find the tree of life.)
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 ago
  Yes, 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 ago
    Yes, 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 ago
  I 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.

garmaine 7y ago

Viruses are life, but they depend on the machinery of other, more complex life to reproduce. Life doesn't start with viruses, for if it did, how would they reproduce?

chongli 7y ago
You asked about examples of life simpler than bacteria. You didn't stipulate that they had to be ancestors. How would that even work, anyway? An organism would have to be extremely long-lived to be living concurrently with its direct, more complicated descendent.
- TeMPOraL 7y ago
  > How would that even work, anyway? Think in terms of lines, not individuals. Mutations are acquired on individual level, so out of a whole family of bacteria, one individual may reproduce into something slightly different, while the rest of the family continue unchanged. (Modulo fast mutation rate in bacteria, and modulo the wide use of horizontal gene transfer. The more I learn about bacteria and archaea, the more I feel there's little point in trying to find the tree of life.)

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 ago
Yes, 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 ago
  Yes, 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 ago
I 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.