Natural Selection

[Xerxes]

One has to keep in mind that "changes in allele frequency" is not the definition of evolution per se, but it can serve as a minimal definition.

Well, it is the accepted definition of evolution. If change in allele frequency is a "minimal definition", you might first explain what this term means (for myself I have no idea), and second, if it does have meaning what the "non-minimal" (= maximal??) definition is.

[CharonY]

You got it from me! I'm the one that posted it.

nope, I copied it from another site, but then I probably just overlooked your quote.

You will note however that the definition of the NAS is not precisely the same as Futuya's, which you brought forth in the first place. And these two are not the only definitions that are currently used by biologists.

 

You never made any statement that Futuyma's definition of evolution was not "sharp".

Well, I thought I implied it.

Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population...to the successive alterations that led from the earliest protoorganism to snails, bees, giraffes, and dandelions

Here essentially Futuyma states that biological evolution begins with changes in allele frequencies and ends with the diversity of species as we have now. This reflects my point of view also. Apparently this is the main point of our disagreement, though. Yet if one explores the statement "descent with modification" closer I'd say it is not too far from change of allele frequencies over time. It does not (at least as I would interpret it) require speciation for instance. And everything below that would be a shuffling of alleles. Yet, it does not define how much shuffling is needed to accept it as a evolutionary process. And this in turn also has an impact on evolution of proakaryotes. Here you do not have easily definable endpoint frequencies (e.g. fixation) due to extensive horizontal gene transfer.

BTW the genetic species concept as applied to prokaryotes is an extremely arbitrary distinction (70% hybridization).

 

re fixation:

Which I had already decided I misspoke when I said that. Look post #71.

Well I am apparently misinterpreting you but this:

When evolution -- changes in populations -- happens, some alleles must become fixed and other alleles must become lost.[/Quote]

gave me the impression that you defined fixation as a prerequisite for evolution?

 

 

Xerxes:

Well, it is the accepted definition of evolution.

I'd rather say that it is one accepted definition of evolution. As you will note from lucaspa's posts it is not undisputed (and rightly so).

I'd say that changes in allele frequencies is the minimal definition because this is the proximal result of evolutionary effects. On the "maximum" side one could argue that once we obsever specietion we know that evolution happened.

[lucaspa]

nope, I copied it from another site, but then I probably just overlooked your quote.

 

Well, it was in this thread. And you are using the same ellipses I am.

 

You will note however that the definition of the NAS is not precisely the same as Futuya's, which you brought forth in the first place. And these two are not the only definitions that are currently used by biologists.

 

NAS is writing for a lay audience. Thus there defiinition is not as detailed as Futuyma's. However, I can't see anywhere that their's is in contradiction to Futuyma's.

 

Well, I thought I implied it.

 

In which case, you need to demonstrate how it is not "sharp".

 

Here essentially Futuyma states that biological evolution begins with changes in allele frequencies and ends with the diversity of species as we have now. This reflects my point of view also.

 

That isn't what Futuyma states. Let's look at Futuyma again:

 

"Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportions of different forms of a gene within a population, such as the alleles that determine the different human blood types, to the alterations that led from the earliest organisms to dinosaurs, bees, snapdragons, and humans." Douglas Futuyma, Evolutionary Biology, (1999) pg 4.

 

Note what I bolded. Futuyma is staking out the boundaries -- the "big tent", if I may borrow a phrase from Phillip Johnson. What you are reading is a progression that says changes in allele frequencies is all you need to get new species. "begins with ... and ends ''.

 

But to get the diversity of life we see now, you need more than a change of allele frequencies. For instance, the peppered moth has vacillated and you don't have any more diversity in species that you had before. Same with the Grant studies on the Galapagos finches. This is Mayr's point: change in allele frequencies is not enough -- by themselves -- to get a new species.

 

Yet if one explores the statement "descent with modification" closer I'd say it is not too far from change of allele frequencies over time. It does not (at least as I would interpret it) require speciation for instance.

 

But it includes speciation. "change in allele frequencies" does not necessarily include speciation. It can include that, but as I keep pointing out, there are numerous examples of changing frequencies without getting a new species. "Descent with modification" is necessarily going to include both micro and macroevolution -- since macroevolution is also "descent with modification".

 

And everything below that would be a shuffling of alleles. Yet, it does not define how much shuffling is needed to accept it as a evolutionary process. And this in turn also has an impact on evolution of proakaryotes. Here you do not have easily definable endpoint frequencies (e.g. fixation) due to extensive horizontal gene transfer.

BTW the genetic species concept as applied to prokaryotes is an extremely arbitrary distinction (70% hybridization).

 

re fixation:

 

Well I am apparently misinterpreting you but this:

lucaspa: "When evolution -- changes in populations -- happens, some alleles must become fixed and other alleles must become lost. "

gave me the impression that you defined fixation as a prerequisite for evolution?

 

Sigh. You didn't read post #71, did you? Yes, I mistakenly did give that impression. Since you apparently won't go back and read the post, let me quote it here:

 

"Let's start from the top. #1 is correct and my original claim was poorly worded. It does look like I'm saying that shifting allele frequencies within a population is not part of evolution.

 

"Biological evolution may be slight ...; it embraces everything from slight changes in the proportions of different forms of a gene within a population, such as the alleles that determine the different human blood types" Futuyma op cit, pg 4

 

Instead, what I meant to say was that loss of alleles and fixation of alleles is an inevitable result of evolution -- common ancestry:

 

"The geneology of the genes in the present population is said to coalesce to a single common ancestor [individual]. Because that ancestor represents one of the several original alleles, the population, descended entirely from that ancestor, must eventually become monomorphic: one or the other of the original alleles becomes fixed (reaches a frequency of 1.00)" D. Futuyma, Evolutionary Biology, pg 299

 

Of course, that means that the other is lost.

 

So, let me rephrase: When evolution -- changes in populations -- happens, some alleles must become fixed and other alleles must become lost."

 

Let me give another disadvantage of the "evolution is the change of allele frequencies" definition.

 

In the creationism vs evolution debate, "change in allele frequency" is often used to try to win a "slam dunk". After all, no one can doubt that this happens. So, evolution is correct, right? Nope, because people extrapolate from that limited definition to macroevolution. And it is here that creationists nail their ass to the wall. Because, as Mayr says and the data says, you can't extrapolate this by itself. There are other processes that come into play during speciation -- the processes that lead to reproductive isolation. And it is argued that there are other processes yet that come into play during macroevolution.

 

So, if you try to go with the "slam dunk" that evolution is "change in allele frequencies" and thus evolution is "proven", the smart creationist is going to reply that changes in allele frequencies don't result in new species, and will cite not only the peppered moths and the Grant study, but all of Fisher's and Dobzhansky's studies in population genetics. Now the whole basis of your position of evolution "proved" is down the drain. The evidence for speciation and macroevolution don't count because "change in allele frequencies" has been "shown" not to result in new species.

 

IF, OTOH, you use the correct, broader definition of either Futuyma or the NAS, then "change in allele frequencies" is only part of evolution. Then the peppered moth and Grant studies become "proof" for that part. And the other evidence on speciation and macroevolution are still valid because they apply to their parts of evolution.

[lucaspa]

Well, it is the accepted definition of evolution.

 

No, it's not. Most evolutionary biologists do NOT accept it. They follow the lead of Mayr, Futuyma, and the NAS and don't use that definition.

 

It is the definition often encountered in online evolution vs creationism debates. But the debators are "evolutionists" but not evolutionary biologists.

 

If change in allele frequency is a "minimal definition", you might first explain what this term means (for myself I have no idea), and second, if it does have meaning what the "non-minimal" (= maximal??) definition is.

 

Frequency is the proportion of individuals that carry that allele. Remember, genes come in several forms -- called alleles. Each allele has a slightly different DNA sequence.

 

Let's take a simple Mendelian example where there are only 2 alleles: A and B. If we have 100 individuals and 90 have A and 10 have B, then the frequency of A = 0.90 and the frequency of B = 0.1

 

Now, if this was a very large population and there was no natural selection and there was no selective mating (completely random mating), that frequency would not change from generation to generation. We would always find that the frequency of A = 0.90 and B = 0.10.

 

However, in this small of a population two things are going to change the frequency of A and B. So, after several generations instead of having 90 individuals with A and 10 with B, you might see 70 with A and 30 with B.

 

Over time, the frequency will shift such that all the individuals will have either B or A and none will have the other.

[Xerxes]

Yet if one explores the statement "descent with modification" closer I'd say it is not too far from change of allele frequencies over time.

For "not too far" read "equal to".

It does not (at least as I would interpret it) require speciation for instance.

What does "require speciation" mean? The definition of evolution? Of course it doesn't, otherwise evolution would be discontinuous.

And everything below that would be a shuffling of alleles.

What do you mean by "below" here? And "shuffling" is most decidedly not what you should say. Do you mean recombination? We are talking mutation here, not recombination (although it can be reasonably argued that this itself is a factor in the evolutionary process)

 

I'd say that changes in allele frequencies is the minimal definition because this is the proximal result of evolutionary effects. On the "maximum" side one could argue that once we obseve speciation we know that evolution happened.

You might. And even if you did, you would have to argue back, using the continuity concept, that the differences between members of population A, over time, are part of the continuum which leads to the emergence, from A, of population B, arbitrarily defined as a separate species. These differences are fully accounted for by change in allele frequency over time. C'est tout.