Evolution of the Genetic Code

[John_Harshman]

@swamidass

What do you mean by purpose?

I mean a selective regime favoring the trait in question.

@swamidass

I’m rather saying that the first individuals to claim the selective benefit of a beneficial mutation are more likely to be more evolvable than their neighbors.

That doesn’t work for natural selection, unless the evolvability trait is tightly linked to the selected trait. Otherwise, the selected trait will spread through the population, but it won’t carry the evolvability trait with it.

@swamidass

I would agree that the much of this process might be neutral initially. However, it causes the beneficial mutations that contribute its selection. So we can’t quite call it neutral draft. There is a causative relationship between evolvability and selection.

But there isn’t, really. The evolvability trait must first become fixed in the population by drift, there being no individual advantage to it, and then it might become more common in the biota through species selection. Species selection can act over a longer time scale than individual selection but is correspondingly much weaker.

[swamidass (S. Joshua Swamidass)]

@John_Harshman

That doesn’t work for natural selection, unless the evolvability trait is tightly linked to the selected trait.

That is exactly what I am proposing. In all the cases I listed, that is precisely the case.

[John_Harshman]

@swamidass

That is exactly what I am proposing. In all the cases I listed, that is precisely the case.

I don’t believe that’s true. I mean “linked” in the genetic sense: not independently assorting. I don’t think that’s true at all.

[swamidass (S. Joshua Swamidass)]

@John_Harshman

That is exactly what I am proposing. In all the cases I listed, that is precisely the case.

I don’t believe that’s true. I mean “linked” in the genetic sense: not independently assorting. I don’t think that’s true at all.

I am meaning linked in a different way. Let us imagine intron splicing helps with evolvability. That means the new innovation would require intron splicing. If splicing machinery is on different chromosome, sorting it away would lose the benefit, and would not be selected. This would be, then, a strong form of epistasis. Not quite linked genetically, but certainly linked phenotypically.

[John_Harshman]

@swamidass

I am meaning linked in a different way.

But that different way isn’t enough to achieve the result you say. You need hitchhiking on the selected innovation in order to fix the intron splicing innovation.