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Comment by gomijacogeo | Hacker News Reader

I think the most likely reason is simply that they were first. And whatever managed to close some metabolic or reproductive cycle first got, and I mean this quite literally, an exponential boost over everything else. So think of early proto-life on Earth not as some single thread doggedly proceeding up an evolutionary ladder, but rather a series of epochs where there's great diversity until BOOM some set of molecules manage to close some metabolic or reproductive loop and then outcompetes everything else in essentially a blink of an eye.

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Couldn't that be the same explanation in the case where it originated here? It was first and dominated?

That's what I was trying to say; I'm in no way a panspermia fan. I was responding primarily to the line "perhaps DNA(+RNA) is the only molecule with the right properties to act as genetic material" with the notion that it was probably more special because it was first rather than something intrinsic about the DNA->RNA->ribosome system that made it inevitable. If we could roll the clock back 4.mumble billion years, we'd probably still get life that had a separation between code and structure, but what that code was and what that structure looked like might have been pretty different.

I'm not sure there is anything else with the flexibility of D/RNA. Its self-replicating property is fundamental. Is there something else known to work anything like this?

Some possible alternatives are covered here: https://en.wikipedia.org/wiki/Nucleic_acid_analogue

And I agree that RNA and DNA are pretty good molecules and probably close to some notion of 'optimal'. The ribosome, however, is big and complicated and there are probably millions of different ways something like that could have come about and that would affect the 3-base codon, protein structures, etc.

Also, look at the contortions DNA has to go through to copy what's called the "lagging strand". Clearly duplicating double-stranded DNA did not come early or easily; it's pretty obvious a system bolted on top of some other, older system. https://en.wikipedia.org/wiki/DNA_replication#Lagging_strand

But that doesn't explain why DNA/RNA is the only. If DNA got a large boost I'll believe it is dominate, but why isn't there anything else somewhere still struggling along.

There is a very (very!) small chance that there are isolated biomes that split from life's tree before what we call the last universal common ancestor (LUCA) and are still plugging along. But it's pretty much impossible that some sister-metabolism from the pre-DNA days could just 'struggle along' side-by-side what we consider 'biology'. When something out-competes another by factors of 1000x or 1000000x, extinction is the only outcome. It's not like elephants and ants finding different niches for billions of years; we're talking about systems of molecules where most of the building blocks are at most a dozen or two atoms and most of the feedstocks are less than 5 (CH4, NH2, O2, H2S, CO, CO2, etc). What's this poor, struggling cousin that we outcompete by a factor of a million going to eat that we can't eat better? Similarly, how does it adapt and evolve against its peers when 999999/1000000 interactions aren't against peers but against us and our self-contained, portable, self-replicating, weaponized Krebs cycle machines?

Re: When something out-competes another by factors of 1000x or 1000000x, extinction is the only outcome.

Maybe it's around, but too small and isolated a population to be discovered.

Or not alive, but fossilized. Speculation gets us nowhere - unless you happen to construct outside alternative life with modern nanotechnology and chemistry, it is bootless to even argue for other forms.

The closest we got is with Threose Nucleic Acids. Managed to get a working hemoglobin binder with this. But it is a relatively obvious analog.

I don't see why 100000x better means extinction must happen. There are "fish" that have copper blood even though iron is significantly better, they are out competed, but that isn't enough to make them extinct: there is still enough oxygen for them to compete.

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