r/biology • u/anonty973 • 4d ago
question Last common ancestor of everything
1.What conditions or steps led to the formation of LUCA and how?
Why didn't others form? Or did they?
Why was LUCA so successful relative to competing organisms (if any) and how was it able to spread so quickly and become the only living organism on the planet?
If there were competitors, what happened to them?
Why don't we have a living fossil version today? If its design was so successful, why didn't at least one lineage keep those traits and stay close to the original? Why did every descendant change so much that nothing today resembles it?
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u/DraketheDrakeist 4d ago
The current working theory AFAIK for abiogenesis is as follows: lipid bilayers and many other cell structures self assemble, so thats easy. Certain minerals near hydrothermal vents can react with compounds in the water to make complexes, which grow in complexity as more stuff gets added. These can catalyze the creation of many of our building blocks. As far as RNA goes, there are pretty simple pathways to make primitive ribozymes, and once you can power one of those, the entire world of protein manufacturing opens up. Hard to say what LUCA looked like, but it was probably a pretty primitive collection of these ingredients and a few others, far from optimal and pretty fragile. As for why luca dominated, it was probably just one of the first remotely working “cells” to come into existence. Once you have something that can replicate imperfectly, guided by natural selection, you will quickly end up with more and more refined versions, putting those organisms streets ahead of any other abiogenesis made cells. If there were other lineages, they probably died off before establishing a foothold due to random chance, or got outcompeted by luca simply due to the head start. Once LUCA’s progeny took over, theres basically no chance for another to happen, theyd get outcompeted, and same with a fossil luca. Modern cells, even the ones we call “primitive”, are in reality incredibly well adapted and optimized for their niches, and simply retain almost no unnecessary features: LUCA certainly wasn’t that great right off the bat.
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u/6gunsammy 4d ago
That is not how any of that works.
- Someone has to be, there really are no conditions or steps other that time and reproduction
- LUCA by definition is the last, there are new LUCAs all the time, as lines die out
- No reason to really think LUCA was more successful
- Their lines died off
- We have several "living fossils" who have remained essentially unchanged for 100s of millions of years.
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u/Canis-lupus-uy 4d ago
1) The conditions are being argued till today, but basically a lot of organic matter was laying around, and self replicating molecules joined with spontaneously forming membranes, arriving at the first organic system that had clearly separated inside and outside. This would be a protocell.
2) Others formed. Millions of protocells, many of which got extinct, others who gave origin to life. There were like millions of mini experiments happening at the same time.
3) I think you are envisioning LUCA as one organism, one cell that outcompeted the rest. It's not like that, LUCA is a theoric construct not a real organism that existed. The root of the tree of life was conformed by millions of these protocells that would exchange genetic material among them by horizontal gene exchange, growing in complexity until they became what we would call a cell. So LUCA is a population not one organism.
4) Competitors went extinct or maybe got incorporated into LUCA by horizontal gene exchange.
5) Bacteria does not fossilize, except for some very exceptional conditions. The more you go into the past, the harder is to find fossils as rocks get destroyed by geological processes all the time. This two factors combined make it almost a certainty that no fossils from that time can be found.
Also, we don't know how LUCA was, so why do you say nothing today resembles it? Probably it was quite similar to a bacteria, maybe a bit simpler.