Interesting series on Mutation-biased evolution at the Sandwalk

I suspect that there is a decently sized overlap between the readers of Peaceful Science and the readers of Larry Moran’s blog, Sandwalk.

However, I just wanted to bring some attention to the fact that Larry is hosting what I suspect will be a very interesting series of posts by Arlin Stoltzfus on the topic of mutation-biased evolution. I’m not overly familiar with the topic, but I think that the series will be interesting and provocative. Check it out!


It is very interesting. Lends support to my argument with @John_Harshman about the evolution of evolvability.

I suspect this dispute is going to be wildly misunderstood in the anti-evolution world.

Ha, probably. I expect that the dispute will be contentious all around.

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He seems like he is setting himself rhetorically as a critic of both the mainstream view and EES.

How so?

They argue evolution is shaped by mutational bias, which is a neglected compontent in some formulations. That supports what I supposed.

If there is variation in mutational bias and some bias is better for evolving fitness, then that mutational bias will be correlated with fitness. Selecting for fitness would select also for better mutational bias, which in turn would increase chances of increasing fitness with new mutations. Thus the evolution of evolvability.

That’s what I see as the key problematic assumption in your argument. What evidence is there for that idea?

Also, that conclusion doesn’t follow. Evolvability, per se, isn’t selectable. It can only hitchhike on the adaptations that occasionally happen as a result of it. And that also requires close linkage between the part of the genome that influences evolvability and the part containing the new adaptation. Alternatively, the evolvability-enhancing feature could become fixed for other reasons, either selection for something else or drift.

All this is more or less group selection, and that’s a very weak mechanism that any amount of conflicting individual selection can prevent.

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That is what I’m saying. It isn’t directly selected but it hitchhikes.

Right. And I’m saying that such hitchhiking requires special conditions that are unlikely to occur and is also too weak and rare to be a significant feature of evolution.

The Evolution of evolvability is a great phrase!

Imagine the those forms of life that developed extremely reliable methods of genetic replication. And then imagine the Earth’s climate swinging once again in some new direction. And so those populations with perfect genetic replication thrived in a perfect fit with their environment and were wiped out as soon as the environment changed faster than their genetics could change…

In contrast, those populations that were very sloppy in their genetic replication, were constantly creating mutations … most of whom perished. And from a human perspective, families were constantly dealing with difficult births or difficult cases of congenital problems.

From a human perspective, it is much better to be genetically unchangeable… than to have all this terrible risk of sloppy genetic replication!

Part 2 is up!

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That’s the part I am not convinced of yet. There are people who point to specific examples of evolutionary pathways that are made more likely by mutational bias, but it seems that there would also be other adaptive pathways that are made less likely by this same mechanism. The only adaptations I can see is in the evolution of codon usage towards conservative non-synonymous mutations due to the pressure from negative selection of deleterious mutations. However, this would limit adaptive pathways that require non-conservative amino acid changes.

I was also wondering if any studies have been done relating to epigenetic mechanisms and mutation bias. The most biased mutations are CpG mutations, and methylated CpG’s are important in gene regulation, so this would seem to be a natural target for people studying mutational biases.

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A new article in the series is up:

I am still a bit underwhelmed. I am just fine with the idea that some beneficial mutations are going to be more common or less common than others due to basic biochemistry that governs how DNA is copied and repaired, but I fail to see how this is anything more than happenstance. The general trend is not towards beneficial alleles. The trend is towards the bias that already exists where transitions outnumber transversions. It seems like the author is making a mountain out of a molehill, unless I am missing something.


It all comes down to whether or not that basic point was really resisted in the field. Seems inconceivable to me, but who knows?

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