alt Hacker NewsThe metabolic science is really cool. The conclusion that life arose twice requires you to buy that proto-cells that grew on these vents and needed those metallic surfaces to survive didn’t count as “life”. Then, free living cells, bacteria and archea, could maybe be argued as having independent paths as they plugged the gaps in their metabolism independently. Same DNA/RNA, same proteins. Same broad rules of metabolism. Just some alternate paths through chemical space to plug in the metabolic gaps and get free from metal surfaces.
To me, these are clearly not independent paths, but rather the branching of proto-life into two of the great kingdoms of life. It’s a stretch to call this two origins rather than a branching.
Then a couple billion years later, one of em ate the other, and rather than destroy it, they both started a symbiotic relationship, and we were off to the eukaryotic race. This is all the same web of life. Not two independent streams.
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> …one of them at the other,
The origin of life is as romantic as I’d hoped.
> The conclusion that life arose twice requires you to buy that proto-cells that grew on these vents and needed those metallic surfaces to survive didn’t count as “life”.
Well, sure. For it to ever be possible to say "life arose more than once," one must decide where the boundary between life and non-life is. After all, every precursor of life arose all at once, in the Big Bang!
You would think there would be some isolated places where proto-life still exists for this to be true.
the Great Oxidation Event caused all kinds of crazy stress = crazy mutations/adaptations where one eventually started our path
* https://en.wikipedia.org/wiki/Great_Oxidation_Event
one of my absolute favorite PBS Space Time on the subject
"proto-cells that grew on these vents and needed those metallic surfaces to survive didn’t count as “life”"
What makes that argument extremely weak is analogies with contemporary obviously living animals.
For example, humans are not alive, because we get 100% of our vitamin D ascorbic acid by scavenging from the environment, along with a handful of other animals that presumably evolved in an extremely vitamin C rich environment. If any animal, including humans, ever evolve a new ability to internally synthesize vitamin C from glucose like every other animal, then given that there were non-synthesizer animals in their ancestry who we arbitrarily define as not-alive aka dead, then we could say that life evolved twice.
Note that humans could be defined as dead because we can't synthesize our own oxygen and have to scavenge 100% of it from the environment using lungs and so forth.
If you pencil whip the English language hard enough, anything with lungs or stomachs is not alive. A similar line of argument would lead to all saprophytes not being alive, which is pretty ridiculous. Wood eating mushrooms are not alive because they rely on the environment to provide all their wood dietary needs. Yeah OK whatever.
The paper claims LUCA doesn't count as life because it still depended on its environment to metabolize.
It's kind of interesting that there's parasites that arguably don't meet this definition either. Looking it up: Chlamydia can't reproduce independently; relies on its host's metabolism. Microsporidia can't make ATP on its own. Are these "life"?