Sunday, February 27, 2011

Extending the Modern Synthesis at the Molecular Level


Question eight for my students is designed to see if they have read and understood three papers that were assigned to them.
G. Ledyard Stebbins and Francisco Ayala wrote in 1981,
During the last decade no other issue has been more actively debated among evolutionists than the role of random drift. Molecular studies have shown that protein polymorphisms are pervasive in natural populations and that protein changes accompany the evolution of species. The neutrality theory of protein evolution proposes that evolution at the molecular level is largely due to random drift rather than being impelled by natural selection. But many evolutionists maintain that natural selection plays an essential role even at the molecular level. The “selectionist” and “neutralist” views of molecular evolution are competing hypotheses within the framework of the synthetic theory of evolution.
Why do they refer to “selectionist” and “neutralist” views “of molecular evolution”? Is there no debate over the role of random genetic drift except at the molecular level? Do you agree with Stebbins and Ayala that Neutral Theory and the role of random genetic drift are usually included in the description of the Modern Synthesis? Did Gould agree when he wrote his 1980 paper?
The quotation is from a paper published in response to Gould's famous Paleobioogy paper where he said that, "I have been reluctant to admit it—since beguiling is often forever—but if Mayr's characterization of the synthetic theory is accurate, then that theory, as a general proposition, is effectively dead, despite its persistence as textbook orthodoxy." (see Good Science Writers: Stephen Jay Gould for a description of what Gould thought of his own claim in 2002.) This paper is now available online. In the past, lots of people referred to it but never read it.

Gould responded to the Stebbins and Ayala paper in Gould (1982). The three papers illustrate the core of the debate over the Modern Synthesis and its possible extensions. I think it's fair to say that modern evolutionary theory has moved away from the hardened version of the 1960s but still not addressed some of the issues that Gould raised thirty years ago.


[Photo Credit: Photograph of Stephen Jay Gould by Kathy Chapman from Lara Shirvinski at the Art Science Research Laboratory, New York (Wikipedia)]

Gould, S.J. (1980) Is a New and General Theory of Evolution Emerging? Paleobiology 6:119-130. [PDF]

Gould, S.J. (1982) Darwinism and the Expansion of Evolutionary Theory. Science 216:380-387. [PDF]

Stebbins, G.L. and Ayala, F.J. (1981) Is a new evolutionary synthesis necessary? Science, 213: 967-971. [PDF]

8 comments:

  1. Prof. Moran, I have been reading your questions, and it all seems to boil down to this: "do you think I am right in my views about evolution?"

    Do you think it's honest to judge the knowledge of other people according to whether or not they agree with you? We have seen a good deal of disagreement in a previous thread in which Richard Dawkins participated. Would you put a D or an F in his test, if he were one of your students?

    ReplyDelete
  2. I would be very surprised if Prof. Moran graded the papers in this way. As a teacher, I look at the ability of the student to create thoughtful arguments using the evidence provided to convince me of their position. How well they do this positions them to do well, not if I agree or not.

    ReplyDelete
  3. Is there any way to get a copy of the 1982 Gould by NOT paying Scribd?

    ReplyDelete
  4. @anonymous,

    I think it's impossible for a professor to teach a subject without having certain biases and without preferring particular models and worldviews. This is especially true when teaching a course about evolution because there are so many controversies.

    I could give a course where I simply present everything I believe and ignore all conflicting data and opinions. That's one way to ensure that my students are effectively brainwashed into believing that I am correct.

    It's easy to teach a course like that and, unfortunately, that's how many teachers behave.

    But I can't do that. I try to let my students know whenever there's a genuine scientific controversy over a particular topic. That does not mean I have to hide my personal views. Students aren't stupid and they can easily see through such a ruse. All they have to do is read my blog.

    Do you think it's honest to judge the knowledge of other people according to whether or not they agree with you?

    No. What I hope to achieve is to sort out the difference between facts and opinions. In some cases this will, indeed, mean that I'm judging the students according to my understanding of knowledge (facts). What are the alternatives? Am I supposed to assume that facts are relative?

    It's a different story when it comes to forming particular models (worldviews) based on that knowledge. That's where everyone is entitled to their own opinion. Just don't try to defend that view using false knowledge or facts (using my understanding of facts and knowledge.)

    We have seen a good deal of disagreement in a previous thread in which Richard Dawkins participated. Would you put a D or an F in his test, if he were one of your students?

    Richard has an adaptationist point of view and that can be a legitimate perspective on evolution as long as it's held for the right reasons and not abused. Some of his arguments are not very logical and he would not receive a good mark if that's the way he answered my questions.

    For example, if he had continued to maintain that all alleles with a visible phenotype are subject to selection, he would lose marks. If he continues to conflate Neutral Theory and random genetic drift as a mechanism of evolution, he would lose marks. If he continues to write as though "evolution" and "natural selection" were synonyms, he would lose marks.

    He has every right to say that adaptation (especially in animals) is the only part of evolution that he's interested in and that's why he pays very little attention to random genetic drift.

    The whole point of these blog postings is to try and mitigate whatever effects my personal biases are having on my students. I'm hoping that some people with different opinions will step up and defend them. How do other professors handle this situation if they don't have blogs? Do they invite in guest lectureres to give the other side of the argument?

    ReplyDelete
  5. Moran:
    If he had continued to maintain that all alleles with a visible phenotype are subject to selection, he would lose marks.

    Dawkins:

    The mythical 'adaptationist' that you have constructed doesn't exist. The hypothesis that horn number is selectively neutral is a null hypothesis waiting to be tested. That's what you do with null hypotheses. You test them: glue extra horns on Indian rhinos, Tinbergen-style, or something like that.

    You, Larry, claim to have an open mind, but it is not much in evidence. You have invented a category of people called 'adaptationists' who insist that all observable phenotypes are naturally selected. All I would really insist is that it is worth testing the null hypothesis that they are not naturally selected.


    I don't think he should lose marks, because he's not saying that all alleles with visible pheontypes have been selected. He's simply suggesting it, and is open to the fact that it MAY not be true. It actually makes sense intuitively, why would an organism expend energy on something that it doesn't need? Granted, it COULD happen by neutral alleles becoming fixed, but which is more likely? The answer is dependent on whether you are an adaptationist or a pluralist, now whether you are right or wrong. The "answer" reflects differences in opinion given the same pool of evidence and facts...or does it understand your "understanding of facts and knowledge"?

    Surely you wouldn't mark a student with a low grade because he or she has formulated their own opinion, which differs from yours?

    ReplyDelete
  6. Hey Prof. Moran, thanks for your reasonable response.

    ReplyDelete
  7. anonymous says,

    I don't think he [Richard Dawkins] should lose marks, because he's not saying that all alleles with visible pheontypes have been selected. He's simply suggesting it, and is open to the fact that it MAY not be true.

    That's what he says today but back in 1982 he wasn't quite so open minded when he said.

    The adaptationism controversy is quite different. It is concerned with whether, given that we are dealing with a phenotypic effect big enough to see and ask questions about, we should assume that it is the product of natural selection. The biochemist's "neutral mutations" are more than neutral. As far as those of us who look at gross morphology, physiology and behavior are concerned, they are not mutations at all. It was in this spirit that Maynard Smith (1976b) wrote: "I interpret 'rate of evolution' as a rate of adaptive change. In this sense, the substitution of a neutral allele would not constitute evolution..." If a whole-organism biologist sees a genetically determined differences among phenotypes, he already knows he cannot be dealing with neutrality in the sense of the modern controversy among biochemical geneticist.

    People can change their minds. But let's remember that this statement in The Extended Phenotype was published three years after the Spandrels paper.

    A student would not get very many marks for making a statement like that in my course.

    It actually makes sense intuitively, why would an organism expend energy on something that it doesn't need? Granted, it COULD happen by neutral alleles becoming fixed, but which is more likely?

    You are demonstrating adapatationist thinking here. To me, it intuitively makes sense that many examples of phenotypic diversity are neutral with respect to natural selection.

    My knowledge of biochemistry and biology tells me that organisms frequently spend energy on things they don't need so I reject the logic of the argument you just made. That's science, not intuition.

    The answer is dependent on whether you are an adaptationist or a pluralist, now whether you are right or wrong. The "answer" reflects differences in opinion given the same pool of evidence and facts...or does it understand your "understanding of facts and knowledge"?

    The difference between the adapationist and pluralist worldviews is a matter of informed opinion. Both views are valid within reason. What I object to is when people defend their views using false logic and misinformation and when they ignore the fact that there are valid opinions that differ from their own.

    Surely you wouldn't mark a student with a low grade because he or she has formulated their own opinion, which differs from yours?

    Nope. But whether the students agrees with me or disagrees with me, they have to defend their opinion using valid facts and arguments. A pluralist student could easily get a very low grade for not being able to adequately defend their opinion and take into account the valid objections of their opponents.

    Most university students learn evolution from adapationist professors. They would be wise not to disagree with the adaptationist perspective on their exams. But that's not likely to happen since the students are not aware of the fact that their professor is presenting opinion in the form of facts.

    My course is different. I'm trying to show students that scientist have diffferent views on evolution and debating those views can be fun and informative.

    ReplyDelete
  8. "My knowledge of biochemistry and biology tells me that organisms frequently spend energy on things they don't need so I reject the logic of the argument you just made. That's science, not intuition."

    Maybe you just haven't found what they need those things for yet.

    ReplyDelete