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Comment by nabla9 | Hacker News Reader

On the contrary. If life started multiple times on earth competitive exclusion probably took care of all other primitive forms rapidly. Even small differences, energy efficiency and reproduction lead to situation where only one form of primitive life survives.

Once the life really started going, it changed the chemistry of the earth rapidly. Similar chemical evolution starting from scratch was not possible once the life started. Eventually when photosynthesis started, biologically induced molecular oxygen caused so called Oxygen Catastrophe where Earth's chemistry turned from reducing into oxidizing. Oxygen also changed the chemistry in the seas and rocks. Molecular oxygen is great disinfectant.

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On the contrary. Life diverges to occupy niches. You will find multiple examples of less efficient processes and body plans living in niches not far from more efficient ones. You can still find all 3 domains of life on earth (Archaea, Eukarya, Bacteria). You can find less efficient photosynthetic pathways dominating their environment (see c4 rice project).

Even the most primitive current life forms are highly optimized and adapted. I don't think the evolution and adaptability of primitive earliest life forms was similar as it is today. Earliest cells were very unstable shaky chemical assemblies and would be eaten by any organism that exists today.

> You can find less efficient photosynthetic pathways dominating their environment (see c4 rice project).

It's not absolute advantage. c4 has advantage in warm and low CO2, low water conditions. In colder climates and with more CO2 and water c3 plants gain more carbon.

How about different chirality? Different chiral forms would have the same advantages.

Most precursor molecules (e.g. CH4, NH2, etc) aren't chiral, so differently-chiral'd proto-life would still compete for the basic building blocks. Each time one set of complexes managed to get more efficient at something, it probably drove more than half of its competitors to extinction. Repeat a few times and you wind up with essentially a single global consensus and the arms-race moves on to higher levels of abstraction.

> Most precursor molecules (e.g. CH4, NH2, etc) aren't chiral, so differently-chiral'd proto-life would still compete for the basic building blocks.

Yes, but horses and cows also compete for the same building blocks. And yet, we have horses and cows.

Your argument could be right if there wasn't an abundance of these building blocks.

And yet we have no more mastodons, dinosaurs, trilobites, ... Stuff still goes extinct, it's just a lot slower with cows than with molecules.

I think you're just failing to grasp the sheer numbers involved here: there are probably around 10^9 cow-like critters and they interact with other, competing critters every, let's say, 10^4 seconds, with the odds of any one of these interactions being fatal being, again, let's say 1 in 10^4. By comparison, there were probably something like 10^37 (if I counted my orders of magnitude right) biomolecules interacting every 10^-6 seconds where every time some new chemical "A-ha!" moment occurred, that reaction now became 1000x more favorable than any other competing reaction. That's like, what, 41 orders of magnitude; even if I'm off by 10+ orders of magnitude, there was just a whole lot more selective pressure going on during the pre-biotic era. Less favorable chemical pathways were outcompeted on scales so vast you'd need trillions of cow-years to approximate how de-de-de-deselected-for they were.

When life forms of opposite chiralities exist in the same place, they compete against each other s by turning precursor hydrocarbons into forms that their mirror can't use. There is also the fact that while polymerization of alternating left and right handed nucleotides is relatively rare, it happens in molecules like siderophores.

Btw. Mirror chiralities are not exactly symmetric. There are tiny asymmetries between chirality due to weak interactions and electron interactions. Weak interactions might affect long hydrocarbon chains. Electrons from beta decay interact with molecules of different centrality with slightly different speeds (difference is something like 0.01%).

https://www.nature.com/news/force-of-nature-gave-life-its-as...

Nature might be slightly biased due to the asymmetry of the weak force.

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