Saturday, February 06, 2010

Talkorigins on five misconceptions of evolution

9 comments:

Bilbo said...

As far as I know, none of the leaders in the ID movement resort to any of these five objections.

Michael Behe, for example, not only accepts common descent, but even presents evidence for it in his book, The Edge of Evolution.

Steven said...

That bit about chance doesn't quite get at the objection, I think.

When someone objects that the theory of evolution amounts to life coming to be and changing by chance, it doesn't help to just respond, "Well, natural selection weeds out the weaker folk, so it's not all chance."

It is pure chance that any organisms fit for survival exist in some locale. It is pure chance that some mutation is beneficial as opposed to harmful--it's not as if somehow, an animal can purposefully bring about a beneficial mutation in its offspring, after all. It is pure chance that some organism with a beneficial mutation actually mates with another organism. It is pure chance that some organism with a beneficial mutation meets another one with beneficial mutations and they reproduce. It is pure chance that their offspring survive.

The chance involved is tremendous and ubiquitous.

Whether or not this is a good objection, I don't know--all I know is that the response doesn't get at the heart of the objection.

Bilbo said...

You're on the right track, Steven. Behe's objection is that even with natural selection, the probability of getting the complex molecular machines of the cell by random mutation are not plausible. He insists that the mutations must be non-random (designed). Recently, a group of biologists carried out a recent study that inadvertently supported his point. They figured out what the ancestral protein had to look like in order to get its present descendant. But then they also figured out that too many unselected (non-beneficial) mutations would need to occur in order for the present protein to evolve back to its ancestral form. In other words, you can't get there from here. Which is Behe's point. And if there can be that much trouble with homologous proteins, then evolving complex molecular machines (which are made up of many proteins), may be out of the question.

I listed the back and forth debate about it here:

http://telicthoughts.com/is-behe-right-about-thornton/

Bilbo said...

To show that Behe accepts common descent, here are some quotes from his book, The Edge of Evolution:

"Evolution from a common ancestor, via changes in DNA, is very well supported." (p.12)

"Over the next few sections I'll show some of the newest evidence from studies of DNA that convinces most scientists, including myself, that one leg of Darwin's theory -- common descent -- is correct." (p.65)

Then from p.65 to p.72 he does, and concludes:

"Despite some remaining puzzles, there's no reason to doubt that Darwin had this point right, that all creatures on earth are biological relatives." (p.72)

"Charles Darwin deserves a lot of credit. Although it had been proposed before him, he championed the idea of common descent and gathered a lot of evidence to support it. Despite some puzzles, much evidence from sequencing projects and other work points very strongly to common ancestry."(p.83)

Blue Devil Knight said...

Bilbo Thornton's earlier work on receptor-ligand evolution already showed up the gaps in Behe's reasoning. It's sort of funny that Behe is now stalking Thornton. :)

Thornton's response to Behe's misinterpretation of his paper is pretty good.

The key is this:
"Behe’s discussion of our 2009 paper in Nature is a gross misreading because it ignores the importance of neutral pathways in protein evolution. We studied whether the key mutations that drove the “forward” evolution of GR’s new function could be reversed in a later version of the GR, restoring the ancestral conformation and function. We found that the later version of the protein could no longer tolerate the ancestral amino acids at these key sites, despite the fact that they had been present in the protein at an earlier stage of evolution.

We identified the specific “restrictive” historical mutations, which occurred after the shift in function, that either clashed with or failed to support the ancestral conformation. If these mutations are reversed first before the key function-switching mutations, the ancestral structure and function can be restored."

Pretty much Behe got schooled, and in Behe's responses (linked by Bilbo) to Thornton, never gets out from the anvil dropped by Thornton. When the primary researcher is like 'Sorry you don't get my paper,' you are pretty much eggfaced. Behe gives some weak mumbling about neutral evolution and how he is well aware of it, but should probably just concede here. He got PWND.

In general the question of the reversibility of evolution is sort of interesting. Obviously nobody in evolutuionary biology claims that going from X to Y in evolution should be as likely as going from Y to X. The scenarios that would explain why are quite varied, not limited to:

1. In the present environment, X is advantageous and Y is not, so unless the environment changes, we don't expect evolution reversal (that's a main point of natural selection).
2. Females in the population could prefer mating males with Y to males with X (males could also have this preference).
3. Y has become embedded in a developmental system such that other crucial functions in the system now depend on Y (e.g., the expression of gene Y became a trigger for other genes that control brain development).
4. Genetic drift, which involves random fixation of a genotype because of sampling bias. If Y is fixed in the population because of such drift, we wouldn't expect it to repeat, as it is stochastic not deterministic in its dynamics.

Thornton has done some great biology. Good to see it mentioned here.

Blue Devil Knight said...

Sorry two mistakes in list at end:
Number 1: switch X and Y. X is ancestral, Y is derived so I swapped them.

Number 4: replace "repeat" with "go the same in reverse".

Also, Steven is of course right that chance is very important in evolution (and not just natural seelction but also genetic drift). The point at the site is that natural selection is not chance. That's a backwards way of looking at it.

Is the schoolteacher who picks the smartest kid in the class acting randomly? Certainly not. But we probably will need to appeal to probability when explaining the variability in her student population.

Steven said...

We shouldn't think of natural selection as a person or a force of some kind. It's not analogous to a teacher selecting the smartest child in her class.

Furthermore, it is presumed that those most fit for their environment will survive to reproduce and pass on their genes--but even this is a matter of chance, given that it could be that all the animals in an area are extremely unfit yet still survive, or they are all fit yet all die without passing on their genes, or they are all fit yet their offspring have harmful mutations, or whatever. It is chance that natural selection "works" in some cases; it's not a law of nature by any means.

Blue Devil Knight said...

Steven: the schoolteacher is an analogy, and a quite apt one. Darwin's analogy was with selective breeding of pigeons. Farmers pick them for certain traits to breed them. That's not random. The variability in the pigeons? That's where the randomness comes in. Of course these analogies are what Darwin called 'artificial' selection, so they aren't identical to natural selection (otherwise they wouldn't be analogies).

Obviously in natural selection the "selection" plays out in terms of who reproduces more, not intelligent agents picking organisms with desired traits.

You could pick anything about any organism and call that "pure chance". E.g., it was "pure chance" that my parents met. That would sort of be a category mistake, as the claim is that natural selection operates over population-level genotypes, not individual-level phenotypes or interactions.

At any rate, nobody would argue that natural selection isn't an important force for evolution. The question is the explanatory scope of natural selection in evolution (e.g., compared to genetic drift and such).

Bilbo said...

Hi BDK, sorry, I hadn't realized that you had responded to my comments. If you go to Behe/Thornton debate, I think you'll see Behe's responses to Thornton.

And good wishes to your expecting family.