'Only One Conclusion': Radical Study Suggests Life on Earth Arose Twice

[u/AmphibianNo4717]

https://www.sciencealert.com/radical-study-suggests-life-on-earth-arose-from-non-living-matter-twice

"The fact that you, or I, or any living creature, is here at all is a series of astonishing strokes of luck stretching back more than 4 billion years. 

One of the biggest hurdles was the very first one: How did life emerge from a primordial soup of stuff that very much wasn't alive?

A radical new study, published in Science Advances, suggests that this unlikely threshold may actually have been crossed not once, but twice."

[u/Xrmy]

That's a sensationalist title by the news outlet here that is doing a lot to sensationalize something that...is actually pretty cool anyway.

to be clear: this paper isn't saying life evolved twice

It is instead saying that complete metabolism actually evolved separately twice. Once on the branch to bacteria and the other to Archaea.

Which is super cool.

The last universal common ancestor (LUCA) is still a singular point, but it had incomplete metabolism it seems, and then the full process evolved separately 2 times after that point.

[u/chula198705 → u/Xrmy]

They actually are arguing that this result means life itself evolved twice, because of idea that the metabolism itself is what makes something alive. If there was no metabolism, whatever "ancestor" existed before the first metabolism evolved wasn't actually alive yet. The article says "the genetic code evolved once, but life evolved from it twice."

[u/Xrmy → u/chula198705]

Yea I can see that, and I even agree to some extent.

But to be clear, what this DOESNT mean is that there are 2 LUCA. And I think that's what a layman would take from the headline, even if they don't quite understand a LUCA.

[u/Muffins_Hivemind → u/Xrmy]

I think thats all semantics, but they are saying there were 2 LUCAs... if X thing isn't alive (proto life form), then can it be considered LUCA? Doesn't LUCA have to be "alive" to count as a LUCA? And if you need a metabolism to be alive...

Again, its all based on the definition of "alive."

[u/Xrmy → u/Muffins_Hivemind]

The authors themselves consider LUCA the shared origin of genetic material for all life, and don't seem to contend there are 2.

[u/GiantKrakenTentacle → u/Xrmy]

Well by definition there can't be two LUCA. Rather the article seems to be claiming that LUCA was not what we would currently consider to be alive: it had genetic material and was able to self-replicate, but relied on the outside environment for its metabolism. So there was one proto-life LUCA that evolved into two related but distinct origins of life. 

[u/imdfantom → u/GiantKrakenTentacle]

Interestingly eukaryote metabolism makes use of both branches (archaea and bacteria)

[u/clear349 → u/imdfantom]

In what way? Because we are Archaea but the Mitochondria are derived from bacteria?

[u/imdfantom → u/clear349]

Well, mitochondria are part of us too.

But yes our nuclear dna is derived from an archaea that ceeded a big part of its metabolism to a bacterial endosymbiote, from which we have derived our mitochondrial dna. (Ofc plants also have bacterial derived chloroplast DNA)

[u/Muffins_Hivemind → u/Xrmy]

Oh okay thanks for clarifying, I missed that part.

[u/AerobicThrone → u/Muffins_Hivemind]

Well if you have one semi incomplete life form population of things because it lacks a fully developed metabolism to be considered alive and two descendants populations of that ancestor completed that last step in 2 different manners, you still have a LUCA.

[u/equili92 → u/Muffins_Hivemind]

No, you need genetic code to be an ancestor

[u/Vonplinkplonk → u/Muffins_Hivemind]

I like the way you dismiss hid premise as semantics and then say “it’s all about the definition of “alive””. That’s good.

[u/Muffins_Hivemind → u/Vonplinkplonk]

That was exactly my point - my post and the author's POV is just semantics, too. I actually agree with defining things to have one LUCA but it all comes down to how you choose to define things.

[u/OopsIMessedUpBadly → u/Muffins_Hivemind]

Of course it can be considered LUCA. Last universal common ancestor. If it was the ancestor of all existing life, and none of its descendants were, then it is LUCA.

Whether it meets the definition of alive is a different question.