The Neutral Theory of Evolution

(George) #86


But you are missing the key point: neutral genetic changes dont stay neutral forever!

Environments change … and what was neutral can become negative or positive … where aggregations
Of hundreds of neutral changes suddenly determine survival or extinction!

(Ashwin S) #87

Why should neutral changes prove useful when environment changes… isn’t it a characteristic of neutral change that it doesn’t have any function on which selection can act. If random chance is the reason… then isn’t neutral evolution even more implausible than evolution guided by natural selection?

(Bill Cole) #88


(Jon Garvey) #89

Not sure about that: many near-neutral changes would be minor alterations of existing functional genes. A bit less of enzyme X might escape selection until an environmental change renders the enzyme a significant hindrance, in which case the lack of function would come under selection.

The same is not true, of course, of non-functional sequences milling around in the genome, suddenly acquing a stop codon and becoming Orfans just when required.

And all of that is a long way from the general idea that the progress from theropod to peacock, or ape to man mainly took place through neutral changes topped and tailed with selection.

(Neil Rickert) #90

There’s no “should” about it.

Some neutral changes might turn out to be useful with an environmental change. And some might turn out to not be useful, to even be harmful.

If there are some that turn out to be useful, those can be the basis for evolutionary change.

(Jon Garvey) #91

Another interesting consideration: of mutations that do come under selection, the vast majority are deleterious. So it is far more likely that a shift in environment will render a near-neutral mutation frankly deleterious rather than than beneficial. In that respect such “mutations in waiting” are no different from mutations under adapationism.

(S. Joshua Swamidass) #92

That’s not actually right. Most non neutral mutations are deleterious in any context, irrelevant of environment. That is messing with your intuition.

(Jon Garvey) #93

But functional mutations can become deleterious in new environments (hence the benefit of knockout mutations), so why not mildly deleterious ones? And why would that not happen more than near neutral mutations becoming beneficial?

(S. Joshua Swamidass) #94

Both can happen. I’m just saying it is more balanced in this scenario. If you take into account the effects of minds, it might skew very strongly towards beneficial. Think about mutations that help an animal tolerate cold or warm weather. The mutations will cause a change inpercieved comfort level indifferent environments, which in turn can cause (by way of comfort seeking) differences in geography and the experienced environment. Along this dimension, no mutations are deliterious, because the interaction with behaiviour is self reinforcing.

(Jon Garvey) #95

Yes - you’ve combined niche construction with neutral theory before, and it makes sense. Still, we’ve got a selection scenario - there’s no guarantee that the change in cold tolerance would not disadvantage the animals with the mutation, which would be moving away from the environment they’re generally adapted for.

Niche construction is also one of those theories, like sexual selextion, that assumes prerequisites, like the nous to construct the niche when your genes start messing you about. Your example of feeling cold is nice and simple, but it also has to explain anteaters and moles.

Blimey, straight from Romans 5 to niche construction. This never happens in seminaries, I bet.

(Ashwin S) #96

It seems to me that neutral theory of evolution is more compatible with a “structuralist” view of Biology in contrast to the “trial and error- random chance view”.

Thinking along these lines can eliminate a lot of perceived weaknesses in the theory while opening up a totally new can of worms… Esp with respect to metaphysics.

I wonder whether there is any scientific basis to completely exclude structuralism as a possibility and only view neutral mutations as accidents of nature.

Edit: Perhaps the proper Null hypothesis to common Descent is not seperate ancestry… but Structural constraints at every level…

(Joseph Akins) #97

I think it’s more that the organism does anything vs. any concern about what it means to “know” that troubles me. The organism putting things in the attic to use seems too Lamarckian. I see the teleology only at the molecular level as “being biased toward useful stuff”. This is why I accept neutral drift, but within preset boundaries. What exactly the boundaries are, or how they are implemented, is another matter.

(Joseph Akins) #98

No, I understand that neutral genetic changes can lead to variation in structure with some positive and some negative depending on the environment. It’s the timing and control of their production, their regulation, that has not been explained.

(Jon Garvey) #99

Is the allocation of funds and control of teaching institutions a “scientific basis”? :grinning:

(Ashwin S) #100

I am led to understand that that is some thing completely political in nature… :slight_smile:

(George) #101


Are you attempting to say ALL neutral mutations are neutral FOREVER?

When the plague roared through Europe… there was a configuration of genes which apparently offered humans no advantage (since it only existed in about half the population)… for centuries…UNTIL the Plague.

And then almost all humans in urban areas without this configuration DIED.

If something is neutral for centuries… This is not the same as ALWAYS being neutral.

And if it takes more than a century to find out … it dramatically affects how you define NEUTRAL.

(Ashwin S) #102

No I am trying to say the below:

That better ways to explain how neutral mutations lead to novelty than chance are required.

(George) #103


Either way… God provides for it.

But in terms of comprehension… if Neutral changes are forever neutral…it will not lead to anything ever.

(Steve Schaffner) #106

A more likely scenario: a stretch of sequence (including stop codon but lacking a promoter or any other regulatory sequences) generates a useless peptide when it is occasionally and randomly transcribed. When the environment changes, the peptide suddenly becomes useful. Any mutations (e.g. one that creates even a minimal promoter) that increases transcription is now beneficial.

(Steve Schaffner) #107

I think the neutral theory is almost completely orthogonal to structuralist claims. Really, all the neutral theory said was roughly, “Oops, turns out there’s a lot more genetic variation than we expected there to be, or than could plausibly be explained by positive selection. Most of it must not be doing much of anything.” Since the specific sequence in the bulk of the genome also turns out not to be doing much of anything, it’s hardly a shock that most mutations don’t either. (This is true for species like humans. It’s not really true for bacteria, and it isn’t at all true for viruses.)