+1 but does this argument work for heterochirality?

@uhoh You mean systems that use both chiralities at once? Those would be much more complex and thus expected to be selectively disadvantaged.

No. Your answer is based on the idea that if two (or more) biologies exist, one will have some advantage over the other. The biology that is currently on Earth (that we know of) exhibits homochirality (1, 2) but presumably precursors to life would have had both chiralities. There could have been parallel biologies right here on Earth early on with neither having a competitive advantage over the other, and I don't think your answer currently covers this case.

@uhoh: This answer directly addresses that: it raises the question in the second half of the second paragraph (giving that exact example!), and dedicates the third paragraph to answering it.

@ruakh I'm seeing Mitochondrial Eve and Y-chromosome Adam; these are proven examples of "all lineages are equally fit."? Equal fitness is known to be true in these cases, or is that an assumption?

@uhoh: If you don't believe in that example, feel free to ignore that sentence. It's just an example; the argument doesn't depend on it.

@ruakh No, they didn't, it avoided it. I'll wait for the author's response on this; I don't see a convincing argument that when "all lineages are equally fit" one will always annihilate the other(s). The answer says this is so and links here but they may want to elaborate more on it.

@uhoh: You may not see a convincing argument, but your initial comments implied that you literally didn't see any argument. (For example, you wrote: "Your answer is based on the idea that if two (or more) biologies exist, one will have some advantage over the other"; but in fact, the answer explicitly covers the possibility that that's not the case.) Now that you know better, there's no shame in deleting those comments and posting a new one with your current question.

@ruakh Like I said, I'll wait for the author's response.

@uhoh ruakh has it correct. If all lineages in a population are equally fit, eventually one lineage is expected to become dominant. If some lineages are more fit, they will dominate more quickly.

@jakebeal I don't (and haven't) necessarily challenge that. I'm just looking for how that's supported; how one goes beyond simply saying so. Where does "... is expected..." come from in cases of "equally fit" biologies?

@uhoh does the link to a peer reviewed journal not count as support?

@Tim only if it is explained how the link supports it. Which of the links do you think does, and exactly how does it? That's all. (at)jakebeal is an articulate answer-author, we don't need 3-against-1 to address a simple question. Let's keep it uncluttered here?

@uhoh doi.org/10.1038/nature02745. I don’t know how it supports it because I’m not an evolutionary biologist! That’s the point of this answer (and all SE answers): to simplify the complex science into something you and I can understand! The “convincing argument” you’re looking for is in that journal article!

@uhoh your simple question says “I don’t think your answer covers this case” but the answer clearly says “converges towards elimination”. Now you may disagree that it is true, but the answer very clearly does cover that case!

@Tim Biology SE's user community his quite heterogeneous, not everyone comes here "to simplify the complex science into something you and I can understand". Some come to address the science head-on. Folks will naturally differ on where the line between "address" and "mention" falls.

@uhoh I attempted to summarize the key results of the article in the final two sentences of the paragraph: "Biodiversity is constantly being gained through divergence of existing lines and lost through lines that fail to reproduce. Over many generations of reproduction, this produces a random walk pattern that converges toward elimination of all but a single lineage in a given population even if all lineages are equally fit."

If you could expand on what aspect of this you are finding unclear, I'd be happy to try to clarify.

It doesn't matter how many times and how clearly one expresses something, supporting it is a separate task. I wrote "I don't see a convincing argument that when "all lineages are equally fit" one will always annihilate the other(s). The answer says this is so and links here but they may want to elaborate more on it."

Does one of the links support that specific assertion? If so, just block-quoting the specific passage would do it for me. I've also offered to ask a separate question about heterochirality if that helps.

Some of the other commenters tried to equate "how do we know this is true" with "I think you are wrong" and that seems to have confused the discussion.

Maybe the threshold for supporting assertions is lower in Biology SE than other science-based SE sites? Chemistry SE is pretty strict about such things, and geneticists are fastidious about it in general. Anyway I'll see if I can write up a new question about chirality and ping you here if I do.

@uhoh Sure, I can lead you through the logic from the paper. If you look at Box 1, you'll see the result giving a power-law distribution of population member uniqueness.

This result implies that as the number of generations increases the fraction of individuals that can have a maximal uniqueness value decreases.

Given integer-valued individuals, a necessary corollary is that when the value is less than 1, extinctions are occurring at an expected rate that increases as the fraction approaches zero.

Note that the result is scale-free, which means that it applies to molecules at a planetary scale just as well as it does for a endangered group of tigers in a biological park.

The time constants are longer for larger group, but deep time is very deep indeed.

I've just finished up a separate answer there based on the two papers I'd linked to in my comments above. But I really appreciate your reply! I'll take a look at these, will take some time as I'm out of my depth but I'll dig in. Thanks!

"Box 1" is in which of the papers you've linked to?

The nature paper.

The others aren't papers, just wikipedia. :-)

PS: on an entirely separate and self-serving note, want to support our Synthetic Biology SE proposal? area51.stackexchange.com/proposals/125068/…

Just read your answer --- nicely written, and I believe a fundamentally similar result.

If I'm understanding correctly from my initial skim, both are self-organization results based on random fluctuations, though the particular details are different.

Like I say, I'm out of my depth here so I can't say for sure right now. I would love to but they make it hard for a feeble-minded user like me...

I don't understand the need to get involved with email just to support an Area51 effort.

Looks like you've already successfully linked your Area51 and main network accounts, so it should be just a button-click if you choose to do so.