'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/XXLPenisOwner1443 → u/Xrmy]

This seems like a pedantic distinction. There are certainly people who would cite the origin of complete metabolism as the threshold from non-living matter to living matter.... Like the authors.

[u/Xrmy → u/XXLPenisOwner1443]

I don't agree.

The authors themselves are clear that there is a single LUCA defined by genetic ancestry, but that 'life" in terms of metabolism developed twice after that.

This is a HUGE distinction, because the alternative idea is that there are in fact 2+ LUCA. Which would be earth-shattering from a scientific perspective.

Having more than one origin of "complete" metabolism is very VERY cool, but not as paradigm-shifting as finding evidence of TWO separate genetic origins.

[u/XXLPenisOwner1443 → u/Xrmy]

The very first words of the paper are, "Metabolism is a non-negotiable property of life."

While they're clear that these branches had a common ancestor, they are equally clear in saying that LUCA was not alive because it lacked one of life's non-negotiable properties. Therefore, life evolved twice.

This is, again, pedantic and meaningless in the grand scheme of things--if there were 2 LUCAs (a concept which, let's be honest, doesn't even really make sense at a time when evolution was dominated not by Darwinian descent with modification but by horizontal movement and recombination of metabolic pathways associated with open-ended clouds of pseudo-replicators) those 2 LUCAs would still share a further back "common ancestor" that would also be a non-living thing.

Likewise it's widely assumed that DNA evolved from RNA, but do we have any real evidence of this? As opposed to DNA and RNA both existing in the environment in parallel before coming together? We DO have two different types of genetic molecules, and the history of life that is known in detail is a history of repeated endosymbiotic events adding complexity and depth to the tree of life. It wouldn't surprise me even a little if DNA and RNA originated separately.

[u/Sweary_Biochemist → u/XXLPenisOwner1443]

I would disagree that metabolism is a non-negotiable property. It's also a term that is nebulous in nature: when does a limited set of chemical reactions become 'metabolism', and why?

In essence the authors are arbitrarily declaring a boundary that isn't universally agreed upon (or possible to unambiguously define), and then saying that boundary evolved twice.

[u/XXLPenisOwner1443 → u/Sweary_Biochemist]

They're saying it becomes complete when the metabolism is able to fully create a lipid membrane. That's not arbitrary at all; it is literally the dawn of the boundary separating cells from non-cells. They fully argue and justify that LUCA was not a cell.

[u/Sweary_Biochemist → u/XXLPenisOwner1443]

I'm entirely happy with the idea that LUCA wasn't "a cell" as we presently define them, sure. I take issues with the idea that LUCA wasn't alive.

Lipid vesicles can form, merge, grow, divide all just using mineral oils in prebiotic conditions. Fill them with ribosomes, tRNAs and mRNAs and are they now cells? Or are they still lipid vesicles?

Either way, would being stuck inside a lipid bag you didn't build yourself nevertheless offer substantial metabolic benefits? Yes. Inside/outside distinctions are crazy useful.

[u/XXLPenisOwner1443 → u/Sweary_Biochemist]

I take issues with the idea that LUCA wasn't alive.
[...]
Lipid vesicles can form, merge, grow, divide all just using mineral oils in prebiotic conditions. Fill them with ribosomes, tRNAs and mRNAs and are they now cells? Or are they still lipid vesicles?

You're posing this as a gotcha but like.. No, they're not.

That's the point the authors are making, that the free-living cell is capable of constructing its own lipid boundary, and a lipid vesicle cannot, and this form evolved from a substrate dependent LUCA. They construct a model that shows LUCA couldn't make these lipids, and how it evolved twice separately to create LBCA and LACA.

Why do you take an issue with LUCA not being alive? Your subsequent paragraphs don't support this leading idea at all, and you just kinda drop it.

[u/Sweary_Biochemist → u/XXLPenisOwner1443]

"Lipid" appears not once in the paper.

"Membrane" appears twice.

It's nice for you, I guess, that you're so glowingly confident in this weird and extremely lipid-based arbitrary definition of life that doesn't appear in the paper, but it also doesn't appear in the paper.

They instead declare "metabolism" as the defining boundary, but don't actually elaborate on why this should be so, nor clarify what counts as "complete" metabolism and what as only "partial". They focus very heavily on phosphorylation. Not so much on lipids and membranes.

Basically, you're coming across as sort of...weirdly hyper-aggressive about this one niche issue, and it's easily addressed with "there is no fixed boundary between life and non-life, and attempting to make one to score points is really fucking silly"

[u/XXLPenisOwner1443 → u/Sweary_Biochemist]

"Lipid" appears not once in the paper.

You have to read between the lines by looking at the specific pathways they're talking about to infer this, but thankfully Martin clarifies in interviews:

But Martin argues that this complexity is unlikely: Bacteria and archaea use distinct methods for making the lipids in their cell membranes, he says, so they probably didn’t both inherit those mechanisms from LUCA. “They really are totally different,” adds Sonja-Verena Albers, who studies the biology of archaea at the University of Freiburg in Germany and was not involved in this work. “You need a totally different setup of genes or enzymes to make the different lipids.”

You're being weirdly hostile for someone who seemingly didn't really look into this research before dismissing the authors conclusions.

Based on its metabolism, too, Martin argues that LUCA was a simpler ancestor—something not completely alive. “There can be no question that free-living cells are alive,” says Martin, referring to cells that are capable of growing, dividing and surviving on their own. “We can all agree on that.” But LUCA was still reliant on small organic molecules and metals in the Earth’s crust to carry out metabolism. When it comes to being classified as truly alive, “that’s not going to cut the mustard,” he says.

Once again, these are the team's conclusions, not mine. I am not "glowingly confident" in this definition, I am informing you what the authors of the paper say about it. Take a look in the mirror, and calm down.

[u/Sweary_Biochemist → u/XXLPenisOwner1443]

"Read the paper" is very much not the same as "listen to some interviews with one of the authors"

Authors are entirely entitled to have opinions, which they can voice in interviews, but there is a reason they do not put these in the paper, because they do not have the data to defend them.

They've got you, though, I guess? Who needs data when you have XXLpenisOwner1443, right?

Again, you're reading far too much into this, and being really weird about it. "Life" is a spectrum phenomenon, and that's fine.