Commenter nails the problem with neutral theory of evolution

_{Denyse O'Leary

May 12, 2014

Evolution, News}

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Comment of the day (re Darwin’s natural selection acting on random mutation vs. neutral evolution/genetic drift:

The real problem is not that they are “mutually exclusive”. Obviously, they are not.

The problem is that they are different things, and that there is a repeated shift from one to the other when we ask which of them is responsible for functional information in biology.

The traditional view, defended also by Matzke and by you, is that NS is responsible for that. In that case, neutral evolution is irrelevamt for biological function.

Others, like Moran and Nei, seem to suggest an important role for neutral evolution in generating function. Even if they do not exclude the importance of NS.

Shifting from one model to the other is a smart way to elude analysis. It’s certainly easier to analyze and falsify a well defined model, rather than a slipping one.

The simple truth is that neither can explain functional information, but for different reasons.

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Comments

Piotr:
I haven’t read Nei yet, but I agree with a lot of what Larry Moran says (not that my amateurish agreement carries much weight). Even if the non-random selection component is primarily responsible for the fixation of adaptive changes, its operation is constrained by mutations (which don’t happen just because they are needed) and may be helped along by neutral evolution (which prepares the scene for adaptive changes).
I think I have already discussed that in my post #12.gpuccio_{May 12, 2014
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Piotr: "Latitude and longitude are also in some sense “two different things”." They are. But at least they are similar in nature (geographic coordinates for our planet). Instead, drift and NS are deeply different. One is a random process, the other is a process where function has a critical role. Moreover, RV is really a component of the whole process described as RV + NS. Drift instead is rather apart, a variation of RV. It happens, together with RV and the rare cases of NS. But RV and NS can happen even if there is no drift. And drift has no "interest" in NS. (Please, don't attack me for the metaphor! :) )gpuccio_{May 12, 2014
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Piotr:
You are putting things in my mouth (and I suppose Nick’s, too). I don’t think anyone in the field seriously doubts that selection is the main engine of the spread and fixation of adaptations, which doesn’t mean that it’s the sole explanation of them (it certainly isn’t responsible for their origin), or that neutral evolution is irrelevant. Note that in real populations drift and selection always act in combination. For example, whether an innovation with a positive selection coefficient has a chance to spread depends on the relative strength of selection against drift. In nearly neutral evolution drift will often override selection, but still the probability of fixation is slightly influenced by the fact that the mutation is not entirely neutral. It isn’t a question of switching between one or the other mode. They are both present.
Well, I think we agree that both drift and NS exist. That is not the point. The point is: what is their supposed role and relevance in trying to explain complex functional information, if you want to exclude design? Let’s suppose that we want to explain how some complex functional protein emerges for the first time at some point in natural history. There are two possible scenarios, if you don’t want to shift components ( :) ). a) Drift has the most important role. RV generates the new sequence randomly, in some non coding non functional region, or in some duplicated inactivated gene. And drift expands it. Maybe in the end, when it becomes an ORF and becomes translated, NS can contribute to its expansion, and certainly can fix it by negative selection, so that it is conserved through time. The strongest argument against this scenario is probabilistic. It cannot empirically happen. b) NS has the most important role. RV generates small variations, in the range that is probabilistically possible, and each new state is a naturally selectable step towards the new functional sequence. So, each intermediate step is translated and confers a reproductive advantage. And, with a little luck (which is always necessary in life) it can be expanded and fixed by NS. Now, this scenario lowers very much the probabilistic walls (the random variations are relatively simple), but there are four big problems with it: 1) To lower significantly the probabilistic walls, you need a lot of intermediate steps. 2) Each step must confer a significant reproductive advantage (IOWs, it must not only be functional, but be naturally selectable). And have a little luck (which is always necessary in life). 3) The individual variations which generate the naturally selectable steps must, for some reason, be exactly those that, when added, generate the sequence for the new, unexpected function. That borders with magic and miracles. That’s what I mean when I say that a complex function cannot be deconstructed into simpler, naturally selectable steps. 4) There is no empirical trace of those selectable intermediate steps, indeed no evidence at all that they even exist. That’s what I mean when I say that RV + NS is an explanation which is neither logically consistent nor empirically supported. Even if you want to propose some intermediate scenario (a little more of this, a little less of that), things don’t become better: a) If you want to rely more on RV and drift, and you lower the number of hypothetical intermediate selectable steps in the model, the probabilistic walls immediately become insurmountable. b) It is difficult to rely more on NS, when there is no empirical example of its role in macroevolution (that is, in a complex functional molecular transition). So, as I said (speaking of drift and NS): “The simple truth is that neither can explain functional information, but for different reasons.”gpuccio_{May 12, 2014
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Piotr, Aren't you just trying to say that evolution happens but mutations that are either somewhat useful, or not useful at all-and we have no idea what percent each is. Is it a useful point?phoodoo_{May 12, 2014
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“They are two different components of the same thing”. Are you happy now? After all, two different components are two different things, aren’t they? “Thing” is a rather flexible word (one of my favorite, when I want to remain generic).
If you want to point to a location somewhere on Earth, you can do so by specifying its geographical latitude and longitude. Latitude and longitude are also in some sense "two different things".Piotr_{May 12, 2014
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Piotr, Obviously it is YOU who is clueless as what I said is spot on. And it is very telling that all you can do is spew your nonsense as opposed to actually making a case.Joe_{May 12, 2014
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Piotr:
No, they are not “different things”. They are two components of the same thing — the variable survival of alleles. Drift is the purely random component (accidental sampling error) and selection is the bias (in response to environmental and “internal” pressures).
Well, how is it that as soon as we start discussing drift and NS, we have to fight about words’? Without reason, I would say. However, as fighting about words with linguists has recently become my favorite pastime, let’s say that: “They are two different components of the same thing”. Are you happy now? After all, two different components are two different things, aren’t they? “Thing” is a rather flexible word (one of my favorite, when I want to remain generic).gpuccio_{May 12, 2014
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In fact why not just say, drift is the inheritance of useless mutations, and NS is the inheritance of (supposedly) somewhat useful mutations. Not that complicated of a distinction really. Neither has much explanatory power for building a complex structure that is novel and useful.phoodoo_{May 12, 2014
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Joe @2, I agree with you. I have to say, I can't understand why there is even a discussion about the difference natural selection plays on evolution as opposed to some "neutral theory" . To me its sort of a pointless distinction, natural selection does nothing. Its not even a thing, and I think its intellectually of those who continue to speak of it as having some power of doing anything. Organisms become whatever they become, and NS has nothing to do with how they got that way. The neutral theory, or any other way one wants surmise why genes are conserved its a useless distraction towards understanding how complex features arose, which utilize multiple parts. Could a collarbone ever be neutral? Or an ear canal? I don't know what I am missing, but it seems a dumb point to linger on by those who choose to do so, to me.phoodoo_{May 12, 2014
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Piotr: I have just won the prize of my life, and you instigate me against Joe? And I believed you were a friend! :) OK, now that's what I will do. I will read your comment on the other thread, and will answer you here. After all, walking around (even randomly) is good for health.gpuccio_{May 12, 2014
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News: Thank you. I am honored! :)gpuccio_{May 12, 2014
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Oh, Joe, clueless as usual. I'll leave it to Gpuccio to clarify things for you.Piotr_{May 12, 2014
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Natural selection does NOT act on mutations. Mutations are part of natural selection. And mutations are also part of drift. The difference is that natural selection is differential reproduction DUE TO heritable random mutations and drift is just heritable random muations.Joe_{May 12, 2014
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https://uncommondescent.com/evolution/there-is-no-neutral-theory-of-evolution/#comment-499919Piotr_{May 12, 2014
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