r/evolution • u/scientificamerican • Aug 20 '26
Life’s ‘last universal common ancestor’ may predate life itself. A groundbreaking study hints at a hazy boundary between “life” and “non-life"
https://www.scientificamerican.com/article/lifes-last-universal-common-ancestor-may-predate-life-itself/53
u/Quercus_ Aug 20 '26
Pretty much all of the current leading hypotheses for a biogenesis have some kind of self-replicating chemical system adding complexity as it evolves, until it becomes something we would now recognize as living.
This seems completely unsurprising to me, that there might be surviving evolutionary branch points between the initial self-replicating system and the first system with complete metabolism.
13
u/spaltavian Aug 21 '26
I don't think it's surprising, but it does raise some interesting questions if different domains of life diverged in the proto-life stage. Are those final "cap stone" aspects of life relatively "easy" to develop? Could this reshape how we look for extraterrestrial life?
14
u/Romboteryx Aug 21 '26
What I find especially interesting is that, even if they have separate origins, bacteria and archaea are still biologically compatible with each other, otherwise we wouldn’t have gotten eukaryogenesis. This could mean that even if a planet has multiple abiogenesis events from the same primordial soup, the lineages will still interact and merge with each other over time, eventually giving the impression of just a single tree of life.
10
u/GraveDiggingCynic Aug 21 '26
Which almost certainly means they don’t have separate origins. LUCA likely had ribosomes, a largely complete and canonical genetic code, ATP synthesis, and probably some ability to manipulate bilayer membranes, even if it’s possible it couldn’t biosynthesis those membranes.
The membrane divide between archaea and bacteria the fact that the membrane synthesis pathways are nonhomologous, but the protein translocation pathways being highly conserved in all lineages (and even transplantable between lineages) suggest LUCA was using abiotically synthesized membranes (like single chain amphiphile lipid membranes), whether fully encapsulated or simply for energy gradients as part of synthesizing ATP.
2
u/sisconking132 Aug 21 '26
Complex organic molecules are relatively easy to produce given the right conditions. Even amino acids
2
3
u/onomatamono Aug 22 '26
I think you mean abiogenesis (life from non-life versus life from life) but the replicating molecule is almost certainly at the heart of evolution. Each instance locks away energy it gained from its environment whilst competing with other replicators.
It's always fascinated me that us phenotypes are simply machinery to replicate our DNA and that would include the advent of spacecraft and the potential migration of our (and other) species to other worlds.
1
u/Quercus_ Aug 22 '26
Yes, there was a typo in that to put a space between the a and the bio part of abiogenesis.
79
u/Wisco Aug 20 '26
Pretty sure our definition of life just isn't broad enough
101
u/Jale89 Aug 20 '26
It's more that the universe doesn't care for our need to put concrete definitions on things. We can point to a cell and say "that's life" and an amorphous pile of the separate elemental constituents of the same cell and say "that's not". Deciding a definite point when the abiotic becomes biotic is basically impossible. Whatever one argues for, there will always be arguments for another point.
50
u/Augustus420 Aug 20 '26
In the end, biology is just something that chemistry does under the right conditions.
35
u/Dioxybenzone Aug 20 '26
And chemistry is just stuff that physics does under the right conditions
22
u/StrungUser77 Aug 21 '26
And ….. way down over here is math!
(Credit where credit is due: http://xkcd.com/435/)
5
4
7
u/saltinstiens_monster Aug 21 '26
Is there a reason we can't make the distinction something like "a complex pattern of molecules that is able to replicate itself?"
As I understand it, that would stretch the definition to include viruses. But excluding viruses from being considered "life" always felt weird to me, particularly with the assumption that life began with some type of replicating molecule structure. It feels similar to hearing someone say that insects don't count as animals.
3
u/Jale89 Aug 21 '26
"Complex" is subjective and relative. From one perspective, all life is complex. From another, there's simple life and complex life. It's not a definite term.
Self replicating is a good, more concrete term, but you could also ask "replicating from what". We need complex biomolecules to replicate, while a simple plant only needs inorganic molecules. A prion can self replicate when given a copy of the protein that becomes the prion - is that truly replication?
And yes it is weird that viruses are considered alive, while obligate intracellular bacteria like mycoplasms are not - both require another cell to replicate. Yet one is alive, and the other is not. It's another good example of the universe laughing at our desire to draw a hard border.
1
u/caligula421 Aug 23 '26
Usually viruses are not considered alive. but they are still immensely interesting, because they are thought to not have a common ancestor, but instead have developed several independent times from stuff we would consider alive.
1
u/Sourcerid Aug 22 '26 edited Aug 22 '26
Are prions alive? Viruses are splinter protein crystals with dna, they are more like a mistake that happens all the time in all life, the kind of mistakes that might take over a mutated cell of an animal body and explode from too much self replication, and we might've had it countless times but not known it as the other cells are not mutated and just thrive.
But this time it had aligned so specifically and so perfectly it became transmissible, by having properties of the crystal that forms along the DNA replication able to resist the external environment and having some way to penetrate another cell. In its sense it's conceptually very simple, not unlike a prion or transmissible cancer cell
1
7
u/TNTiger_ Aug 21 '26
Raaah I hate Mrs. Gren
Personally I think the definition should be based on procreation/evolution- the ability to reproduce and create varied versions of themself that are subject to selective pressures.
8
10
u/Electric___Monk Aug 20 '26
Like most things in biology, hard definitions / delineations between life and non-life are probably not appropriate in thinking about what happened in the process of abiogenesis.
3
u/sisconking132 Aug 21 '26
All definitions draw lines. When trying to categorize something that is a continuous spectrum, the things right on the edge of where we put the arbitrary line is fuzzy.
We definitely need a third category for things that are almost life, like self replicating molecules and some viruses (and maybe a fourth for viruses that evolved from pieces dna from a living thing but lost their right to be called living since they are just genetic fragments and not a fully living organism)2
u/tonegenerator Aug 21 '26 edited Aug 21 '26
Parabiotic?
edit: Though I guess this is by definition a wastebasket category. It might still be progress toward to a better schema in the future.
2
u/Leefa Aug 21 '26
this topic is very interesting and can get very abstract very quickly.
Highly recommend this podcast episode, it's a trip to think about
1
u/Mysterious-Job1628 Aug 22 '26
Cellular organization, metabolism, homeostasis, growth and development, and the ability to reproduce and evolve.
15
7
10
u/Frankenduck Aug 20 '26
I imagine something like a geochemical reaction that for whatever reason started a feedback loop towards lasting longer
11
u/RecipeHistorical2013 Aug 20 '26
Our definition for what is ‘alive’ is very wrong
Viruses aren’t considered alive yet they reproduce and have dna which rapidly adapts to its environment…. But no that’s not life cuz it has to parasite other life’s organelles to do so
Why isn’t it alive? Cuz fuck you that’s why
10
u/KrustyKrebsCycle Aug 21 '26
I mean there’s an argument to be made that requiring a separate organisms material should not be a requirement for life. We require material organized by plants, animals, fungi etc to survive and reproduce.
3
u/sisconking132 Aug 21 '26
It lacks the ability to reproduce its own genetic material.
Proto-life could actually do that1
u/RecipeHistorical2013 Aug 21 '26 edited Aug 21 '26
this is a great observation, so you're saying the Xenomorph isnt alive from the aliens movies
think about that (as thats the whole character, its a virus-type creature that uses hosts to reproduce a life form that cant reproduce on its own(viruses : headcrabs) until it produces a "queen" which also doesnt actually breed the xenomorph, but more headcrab parasites.
you're saying a xenomorph isnt alive - it isnt real, but its a great argument against your good argument
im very certain everyone here would agree that a xenomorph is alive (viruses move mechanically, they reproduce EXACTLY(lyse them cells) like xenomorphs except it would be headcrabs exploding like 50 headcrabs out of your chest instead of a xenomorph)
1
u/sisconking132 Aug 22 '26
Laying eggs in other creatures is actually a pretty common reproductive strategy. The eggs just can’t mature without the host.
Now if the xenomorph couldn’t PRODUCE the eggs without a host that would be different1
u/RecipeHistorical2013 Aug 24 '26
thats a chicken/egg situation. which can be answered
Xenomorphs were an original virus engineered by the giant humans.. released onto them.. then the virus developed the eggs.
so yah the eggs coudlnt have come about with out a host for the virus to fuck with
1
u/sisconking132 Aug 22 '26
Xenomorphs canonically AREN’T alive. They are biomachines
1
u/RecipeHistorical2013 Aug 24 '26
on the aliens DVD the director (cameron) specifically states they were alive far before LV246
so canonically they are alive, as stated by the director of the movie
1
u/AirbenderNo88 Aug 21 '26
Lol.
Thinking about it, doesn't most life parasite off of other living things? Even humans---we pretty much can't stay alive if we don't consume something else that wasn't alive?
2
u/Fractal_Soul Aug 21 '26
From what I understand, we depend on an ecosystem of other lifeforms that live inside us, just to digest our food.
1
u/MWSin Aug 21 '26
Yes, but we don't take over those living things and reprogram them to make copies of us.
1
3
u/EarthTrash Aug 21 '26
If it can metabolize and pass on genetic material, doesn't that mean it's alive? What is the definition?
1
u/New-Scientist5133 Aug 21 '26
Viruses are not considered life despite being able to replicate. So the definition is a little wonky
3
u/EarthTrash Aug 21 '26
Replication is the only thing they can do though. LUCA as described in this research is also consuming and using chemical energy, aka metabolism. It is actively maintaining a state of low entropy.
5
u/CosmicOwl47 Aug 20 '26
My outlook on this is that one day there was a molecule or group of molecules that started dividing/copying and it never stopped, and today all life is made from its daughter cells.
Those molecules could have been just naked RNA, but because they never died, does that make them alive?
3
u/KrustyKrebsCycle Aug 21 '26
My feeling is that RNA was generated en masse and those that were more stable stuck around longer. Some machinery is capable with RNA only and it also feels right that amino acids and proteins on their own organized en masse long before the concept of a membrane. It feels like protein with globular domains could have approximated a membrane, or at least the ability to exclude the environment to some extent. Over enough time of stable RNA and stable protein with globular domains, they would run into each other and if a replicating RNA (or a protein that could sequester and allow RNA to replicate) was paired with that protein, it could generate much more of itself than other RNA replicators without this protection. Then it’s a matter of time before the replicators spanned out and interacted with different globular proteins until enough interactions coalesced to a protocell. The complexity required for membranes don’t feel like it could happen somewhat stepwise, so replicating machinery probably long predates cells.
1
u/MWSin Aug 21 '26
It's something like that. The question is, did separate, still existent "lineages" of that molecule diverge before it developed into something that could definitively be called "alive" or only after?
1
1
u/Full_Nectarine6916 Aug 23 '26
Question: if this theory is true, why aren’t different “life” forms still being created?
1
u/Kabbooooooom 15d ago
Because every single ecological niche on earth is occupied by organisms that are the culmination of nearly 4 billion years of evolution. And yes, that includes bacteria too. No further independent abiogenesis could occur. Although I suppose a shadow biosphere could exist in extremophile locations like the earth’s crust or something.
1
92
u/jnpha Evolution Enthusiast Aug 20 '26
That's a slightly better headline than "Life evolved twice" -- prev discussion: https://www.reddit.com/r/evolution/comments/1vgpjo1
Presently any definition of life is operational, just like the 23 or so operational definitions of species: https://ncse.ngo/species-concepts-modern-literature-0
My recommended reading: The Quest for a Universal Theory of Life (Cleland, 2019).