Also wasn't the answer always going to be they simply out-competed the other amino acids for that particular role? The research question is why they beat out similarly structured acids to become the consistently dominant ones in life.
So in that context the fact they are so dominant is the key part of the question, not that they are the only ones capable?
> wasn't the answer always going to be they simply out competed the other amino acids
This is a tautological statement: the ones that still exist by definition are the ones which outcompeted the alternatives, because that's what outcompeting means.
The question being addressed by the study is roughly "by what selection criterion did the survivors outcompete the others?"
Sure, my point is the fact that others are still capable of competing can always be assumed in a competitive environment. So in that context, where the question is inherently going to be why did these 20 amino acids out-compete the others, why bring up the fact others exist as a counter-point if the they aren't as dominant as the 20 primary ones? What's interesting is their dominance, not that they can play the game.
I guess it's just nitpicking the headline and is not particularly relevant to the article or the research question (as the OP admitted).
My girlfriend is a biologist and this kind of misunderstanding is IMHO the fundamental difference between a biologist and a programmer. Biology is way fuzzier than computers and that's always the default stance.
Agreed, I took an online "great courses" in chemistry and I had so many "but why?" questions I had to stop. I was spending far too long going down Wikipedia rabbit holes. You need to have a particular tolerance for not understanding it all and work with a sort of bayesian estimation of understanding as you move forward.
That's actually why I switched from physical chemistry to biology. I'm not good with abstract math, and I didn't want to be stuck relying on theoretical stuff that I didn't understand completely.
But TFA isn't about biology. At least, primarily. It's about emulating chemistry that led to the first life forms.
But upon reflection, it's arguable that the paper would have been more interesting if they had included L-canavanine, in addition to L-arginine and three analogs with shorter cationic side chains. Because we know that it can be incorporated during protein synthesis, in place of L-arginine. But none of their analogs can.
So if L-canavanine had been incorporated into peptides in their tests, more or less as well as L-arginine, that would arguably have ruled out their hypothesis.
So in that context the fact they are so dominant is the key part of the question, not that they are the only ones capable?