h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Who is doing the insulting here? I have been accused of being insulting and clutching at straws. What have I accused you of?

True about Lamarck. His followers made most of the cock ups. With regard to acquired characteristics - you have to stretch the concept of 'acquired' quite a bit don't you? Care to give us your favourite example?

Breeding? Animal husbandry? Selection? Crossing?

I see your point, but no matter what label you give it, it is clearly different from the case of industrial melanism.

Breeders see certain desirable traits in an individual (generated by sexual recombination, mutation, whatever) and deliberately try and increase that phenotype by breeding with another dog. This process repeated for hundreds of years for an array of traits has created the various dog breeds we see today.

Industrial melanism, whilst unintentionally triggered by man, was just a highly visible example of evolution and natural selection. What if a volcano exploded near Manchester and covered the trees with soot instead of chimney soot? Would that make the example of industrial melanism more "natural" for you, even though it would have the same effect? The way in which the trees became dark is relatively unimportant, it is the *response by the natural population* of moths which is of interest. That a *natural, already-present* melanic form of the moth (albeit at very low levels) was suddenly at a huge fitness advantage and the allele spread through the population rapidly via gene flow, drift and natural selection. The population adapted, it *evolved* to fit it's new habitat that it found itself in.

Ste

You slip in the word 'evolved' in that last sentence. I did mention volcanic dust a few posts ago. The population adapted through natural selection. Do you deny that? If not, then Occams razor shaves off any further description in terms of evolution does it not? Don't you agree that evolution involves mutation as a necessary condition?

I was referring to the sarcastic Lamarkian Society comments. Never mind.

Heat Shock Proteins in Drosophila. They are molecular chaperones that protect the cell's constituents during times of heat stress. It was found that HSP90 in Drosophila prevented some forms of genetic variation from being expressed. When HSP90 was disabled by cold or heat stress, this variation came out in the form of abnormalities. After a few generations of selection, the abnormalities happened independently of the levels of HSP90. Usually evolution works by the environment selecting the individuals that just happen to be the most well adapted. In this example it is the environment (heat or cold stress) that has allowed the normally hidden genetic variation to be expressed by disabling HSP90. A small amount of selection can then lead to the expression of the variant traits, even when HSP function is restored. Hence, a character that was acquired has been inherited. (From A673319, couldn't be bothered to write it again. Though I want to someday because I think it could be clearer, but oh well).



Ste

No Nog, you're just flat wrong there. Whether something is evolution depends on the process involved, not the outcome. You surely see that as soon as I say it. For the benefit of others. If I paint a dog blue the outcome is a blue dog. That doesn't make it evolution.

I missed your volcanic dust reference, sorry. I'll read back more thoroughly.

The population did adapt through natural selection. However, more than natural selection had to happen, such as mutation, for the population to adapt.

You say that only natural selection is needed, then say that "evolution involves mutation as a necessary condition". Which one do you take to be true?

Ste

OK. That can be seen as a Lamarckian process I guess. Or maybe it can be seen as a forced mutation where one is already incipient. I'm a bit too sloshed to worry and I don't think it has a bearing on the point of the distinction between what processes are evolutionary and what are just selective. Do you disagree that mutation has to be a defining characteristic of evolutionary change?

What I'm saying is that only natural selection is needed to favour one of the existing variations in the existing gene pool. That is not evolution. If, however, a further variant comes into existence through mutation, then the potential for evolutionary change arises through differential selection of that variant. Usually, of course, it is selected out. But just occasionally, one is adaptive and that's evolution.

"Do you disagree that mutation has to be a defining characteristic of evolutionary change?"
No, I agree.

"...only natural selection is needed to favour one of the existing variations in the existing gene pool."
That is only true if you ignore how the "existing gene pool" came to be in the first place, and presume that it's simply "there". Intraspecific variation happens by mutation, etc., etc., without this natural selection is impossible because you'd have a uniform gene pool. To isolate natural selection from it's evolutionary counterparts is erroneous.

If you *choose* to see natural selection in only a limited time frame, that is, the time frame in which natural selection is doing it's dirty work, then you wouldn't see any mutation, etc., just natural selection, but that wouldn't make sense, and seems just a bit narrow in focus.

(Sorry for the pause in the conversation, I had to leave work at that point or I would have been there all night.)

Ste

Yo Ste. I only just crawled out of me pit. Good timing!

See my post #72 in reply to Noggin for the timescale, volcanic dust etc.

After a wobbly start, we seem to be more or less in agreement! That makes a change since it appears to have been a 'get toxxin' day in general. Noggin, of course, is invariably an excellent fellow who just makes his highly intelligent points without any personal attacks.

If the peppered moth became uniformly khaki over several generations, one would suspect a mutation that turned out to be adaptive. That would be evolution. Failed mutations (ten a penny) and temporary local advantages to one part of the gene pool (peppered moth) are not evolution. Sure they are components of the evolutionary mechanism but unless they are combined, it makes little sense to refer to them as 'evolution'.

> "You surprise me by arguing against yourself, Martin."

*shrug*
It was a relevant point to make, so I made it. Whose 'side' it helps isn't really important.

Ste and you have struck on the key issue, though, which is that the mutation happened before the selection process in the moth example. It also happened during the selection process as well, though, assuming the peppered moth didn't start reproducing by cloning during the industrial revolution...

-Martin

No not mutation but differential breeding success of the melanic form in the polluted envoronment. No mutation there - just natural selection.

Toxxin, to quote your own words:

> "In fact some sequence of mutations must have given rise to the genetic variation in the moth population."

Which was what I said. "the mutation happened before the selection process in the moth example". IE, the mutation happened continuously over the past million years, while the selection process happened during a couple of decades.

-Martin

I have a slight feeling of going round in circles starting to emerge.

"If the peppered moth became uniformly khaki over several generations, one would suspect a mutation that turned out to be adaptive."
Or a genetic bottleneck, or fixation of the "khaki" allele.

"they are components of the evolutionary mechanism but unless they are combined, it makes little sense to refer to them as 'evolution'"
But this is the crux, they *are combined*, they *are* working together. It is only you who are isolating them!

And I've just noticed that Martin eloquently summed up what I was going to say. The mutations gave rise to "neutral" genetic polymorphisms in the population, accumulating over time, which only became "non-neutral" (to increase the fitness of the individual) once the habitat changed (sooty trees). Therefore you cannot isolate the mutation and natural selection. Therefore is it evolution.



Ste

Yep Martin, I see where you're coming from. Maybe if the earliest form of the PM had been the pale one, then mutation gave rise to the dark form, then the white form was wiped out due to environmental change, we might want to call that evolution. Some academics seem to want to say that there has to be an increase in complexity for changes to count as evolution. It isn't clear that the melanic form is more complex that the pale one, and we don't know which came first.

The other problem with this example is that the phenomenon was localised (as far as we know) to an area round Manchester. Then when the air was cleaned up the population reverted to its former distribution of the various forms of the moth.

I can't really see that as evolution. Is the loss of eyes, for example, evolution? It happens in cave dwelling variants of some species. It's a marginal case, while the development of eyes seems to be a clear case of evolution. The PM seems to be at the extreme of non-evolutionary change, however.

"Maybe if the earliest form of the PM had been the pale one, then mutation gave rise to the dark form, then the white form was wiped out due to environmental change, we might want to call that evolution."
For an organism to evolve, a competing allele is not required to become extinct. It does not matter which one came first. Evolution is adaptation to the environment, an increase in complexity is a by-product (diagnostic, if you will) as evolution can only work upon modifying what it has got.

Industrial melanism has been studied in depth in three different moths: Biston betularia (peppered moth), Gonodontis bidentata and Phigalia pilosaria. The phenomenon has been observed at geographic clines from South East England all the way up to Southern Scotland and in between. There was also a study referenced in Majerus (1998) that compared the frequency of melanic forms from 1959 to 1995 in Merseyside and Michigan, so we know it happens in more than one industrialised nation.

Industrial melanism, whilst nowhere near as dramatic as eye evolution, is still evolution in action. The fact that it is rapid and involved fewer genes and alleles than eyes does not mean that it is not evolution.



Ste

It seems to me that the only point of contention here is really contextual and involves the size of the window you look through. Evolution is the big picture, and you need a big window. If you look through a smaller window you just see the parts, mutation or selection or drift, or whatever, which can be quite properly called by these names in the smaller frame.
Evolution does not necessarily involve increasing complexity. Some parasites evolved from free living organisms have actually become less complex in the process. (If it works, do it.)

Noggin

*dragging the thread back onto topic*

"if it works - do it"

Some questions for y'all.

1) can anyone think up a better wording for 'inspired belief' or 'the god-shaped hole' - both phrases cause trouble?

2) whether or not tg-sh is a function of evolution or of natural selection, do you think that the entry agues it's case lucidly?

3) ditto convincingly?

an author called Ben