Friday, December 04, 2009

Evolution According to Niles Eldredge

 
I've read all of the books by Niles Eldredge. He's one of my favorite science authors [Good Science Writers: Niles Eldredge]. However, I've never really understood exactly what he means when he talks about evolution. He's not a molecular biologist or a geneticist but does he understand the basics of these disciplines? Does he think of evolution as a branch of population genetics or something else? Does he know about random genetic drift?

Some of these questions have been answered in an article that he co-authors with his son in the latest issue of Evolution: Education & Outreach. This is a journal dedicated to teaching evolution correctly. The article outlines a universal evolution curriculum for all grades from kindergarten to university [Lessons from EEO: Toward a Universal Evolutionary Curriculum].
Abstract We propose a human-centered evolutionary curriculum based around the three questions: Who am I? Where do I come from? How do I fit in? We base our curriculum on our experiences as an evolutionary biologist/ paleontologist (NE) and as a secondary level special education science teacher (GE)—and not least from our joint experience as co-editors-in-chief of this journal. Our proposed curriculum starts and ends with human biology and evolution, linking these themes with topics as diverse as the “tree of life” (systematics), anthropology, Charles Darwin, cultural evolution, ecology, developmental biology, molecular evolution/genetics, paleontology, and plate tectonics. The curriculum is “universal” as it is designed to be taught at all levels, K–16. The curriculum is flexible: “modules” may be expanded and contracted, reordered, or modified to fit specific grade level needs—and the requirements and interests of local curricula and teachers. We further propose that students utilize workbooks from online or printed sources to investigate the local answers to the general questions (e.g., “Who am I?”), while classroom instruction is focused on the larger scale issues outlined in the modules of our curriculum.
I don't like the idea of teaching evolution from a human-centered perspective. Our students are certainly used to thinking of biology only in terms of themselves, but isn't it our goal as educators to teach them that this is wrong?

It's the age-old question of whether the best way of teaching is to cater to student misconceptions or confront them.

A key part of any evolution curriculum is defining evolution. I prefer a scientific definition that allows us to distinguish evolution from other process that may look like evolution. The minimal definition is derived from population genetics and it allows us to recognize that different frequencies of blood groups in different human populations is evolution [What Is Evolution?].

Eldredge prefers a different definition in his evolutionary curriculum ...
What is “evolution?” Evolution is the testable, scientific idea that all species of life on Earth are descended from a common ancestor living billions of years ago since life first began on Earth. You can think of evolution as the history of life on Earth—or even as the fate of genetic information through time.

Module 3: What Is Evolution? How Do Humans Fit into the History of Life?

I've always taught that evolution is a process and that it's distinctly different from the history of life. It's like the difference between gravity and the history of our solar system. The formation of our solar system was a unique event that relied upon, and can be explained by, gravity and other general processes. Similarly, the history of life on Earth is a unique event. It can be explained by evolution and other processes but it's not the same as "evolution."

As far as I know, there are no evolutionary biology textbooks that define evolution as the history of life. The Eldredges are proposing a curriculum that's out of sync with most pedagogical approaches to evolution. Is this a better way to teach evolution? I don't think so.

Module 3 also covers the mechanisms of evolution. Adaptation and natural selection are mentioned but the authors go on to say that natural selection is not the only evolutionary process. The others are: speciation, punctuated equilibria, and mass extinctions.

I've always suspected that Niles Eldredge discounts random genetic drift as a legitimate process of evolution. This confirms my suspicion.

I'm very concerned about the content of this article and it's publication in a journal that's devoted to evolution education. If this is what the experts on evolution education are touting as the ideal curriculum then there are only two possible conclusions: (1) they aren't experts, or (2) I'm dead wrong about everything that I've been teaching.

I'm almost afraid to open up the comments on this posting for fear that (2) is the correct answer.



19 comments :

  1. I won't try to tell you you're wrong about the science. But Eldredge's method of conveying the message (whatever the correct message is) is not obviously wrong. Stan Rice at Honest Ab points out (at least at some level correctly) that "most people are more strongly influenced by emotions, gut feelings, and hidden (or not) sexual feelings" than they are by evidence and reasoning.

    Story telling is a primary way we learn about the world and the most interesting stories are always the ones about ourselves. One way to engage people is to make it a story about them. That doesn't mean it has to be the only perspective. Once you get students engaged, then you can work to show them the larger perspective.

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  2. Larry, I disagree about the status of evolution as a process. I think that evolution is an effect of processes like selection, drift, mutation, and so forth. Effect, not cause; pattern, not process

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  3. Prefect says,

    Larry, I disagree about the status of evolution as a process. I think that evolution is an effect of processes like selection, drift, mutation, and so forth.

    Interesting. So, how would you define evolution? Would your definition look something like this? ...

    Evolution is what results when things like selection, drift, mutation, inheritance of acquired characteristics, etc. happen to the genes in a population.
     

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  4. By all means, feel free to write a clear summary of definitions / educational strategies / whatever for the journal!

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  5. I think his definition is the one that applies when someone is making the statement that "evolution is a *fact*" (in contrast to the different definition intended in the follow up "*AND* a theory.")

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  6. John Pieret says,

    Once you get students engaged, then you can work to show them the larger perspective.

    I use that tactic all the time, even on Sandwalk.

    But don't confuse tactics with strategy. The goal is to teach proper evolution and the trick is to use human evolution as a hook to get into the real topic.
     

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  7. Your post prompted me to look up the definition of evolution in several major Evolution textbooks. I checked Futyuma (3/e), Ridley (3/e), Freeman/Herron (3/e), Rose/Mueller; and the definition in The Encyclopedia of Evolution edited by Mark Pagel (a student of Paul Harvey, by the way); they all give similar definitions and do not state that evolution is the history of life. Most books talk about evolution as change within lineages and/or changes in allele frequency. I don't have a copy of the new(ish) book by Nick Barton et al., but I would anticipate that it has a similar definition.

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  8. I usually think of the fact/theory of evolution and the fact/theory of common descent as two distinct but related concepts. I haven't thought about it much, but it might be possible that even if one is shown to be false, the other still stands. However, they might be too related.

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  9. Yes, that would be close to my definition, although like you I feel that gene frequency alterations are only a bare-minimum requirement for evolution to have occurred.

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  10. There really is no need for a definition differenmt from the basic one you described, Larry. If alleles can change within populations,then divergence between populations will inevitably occur. Everything else flows from that. Common descent is an inevitable byproduct of the fact that organisms have ancestors and leave descendants.

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  11. Perhaps this is merely a paleontologist vs. neotologist confusion?

    Eldredge being a paleontologist tends toward thinking about pattern whereas biologists tend towards thinking about process.

    Both are legitimate IMHO and should be, huh, 'cross pollinating' so to speak.

    Your mileage may vary.

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  12. The definition of evolution Eldredge gives is the common non-specialist definition.
    'Evolution' can mean both a pattern and a process.
    Most evolutionary biology textbooks start with the processes and go light on the patterns. Barton's textbook starts with the pattern, and thereafter does the processes. Barton's book does not give evolution as a term in the glossary, or define it in the intro. Since the book mentions 'evolution' and 'evolutionary processes', the idea at the background seems to be evolution as descent with modification.
    Zimmer in The Tangled Bank uses descend with modification.
    I agree with Prefect: evolution is the effect of a series of processes, but should not be identified with these processes.

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  13. Barton, Briggs, Eisen, Goldstein & Patel, 2007
    Evolution

    Page 1:
    Aim and scope of the book.
    "Evolutionary biology describes the history of life and explains why organisms are the way they are"

    This book has in many respects taken its leave from neo-darwinism.

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  14. Heleen says,

    I agree with Prefect: evolution is the effect of a series of processes, but should not be identified with these processes.

    Let's say you're interested in the fact that average Europeans have increased in height over the past 500 years.

    That looks a lot like descent with modification to me. Can you give me your definition of evolution and explain how it helps us decided whether Europeans have evolved or not?

    Let's say you're interested in knowing why American natives have mostly O type blood. How can I tell if this is evolution using your definition?

    As you know, pseudogenes accumulate mutations over time. Is that descent with modification?

    I don't see how you can define biological evolution without mentioning some aspect of the process that distinguishes evolution from all other examples of change over time. At the very least you have to specify that the change must be genetic and that it's populations that evolve and not individuals.
     

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  15. Evolution should not be confused with population genetics. A definition of evolution as change within lineages and/or changes in allele frequency restricts evolution to population genetic processes. Given that evolution had a career as a concept and a science before population genetics came in or took over, this restrictive definition cannot be sufficient.
    Many books start with an introductory chapter 'evidence for evolution' or some such title (chapter 2 in Freeman & Herron 4/e, ch 3 in Ridley 3/e). This evolution is not allele frequency change. Ridley says as a starter in 3.1 : "there are three theories of the history of life ... 1. evolution; (...). "
    That is, evolution is the explanation of the history of life, starting with an interpretation and explanation of the patterns and then as the processes that lead to the patterns. Descent with modification is good description.

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  16. Jerry Coyne wrote a book:"why evolution is true". The book is partly concerned with
    Evolution is what results when things like selection, drift, mutation, inheritance of acquired characteristics, etc. happen to the genes in a population., but that is not what the title refers to. The title is about the explanation of the history of life.

    Coyne's book has three chapters on patterns followed three chapters on processes. This balance between patterns and processes is necessary for a good book on evolutionary biology.

    As to the phenotypic plasticity in human height, this does not come under 'descent' as that is usually read in 'descent with modification'. The second is a bottleneck effect in allele concent, and in the example negligeable as to evolution. The third looks like comparative anatomy at the molecular level, an evolutionary pattern and it is good to know the process.

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  17. Heleen says,

    Jerry Coyne wrote a book:"why evolution is true". The book is partly concerned with
    Evolution is what results when things like selection, drift, mutation, inheritance of acquired characteristics, etc. happen to the genes in a population., but that is not what the title refers to. The title is about the explanation of the history of life.


    Jerry Coyne is a smart guy. He knows the difference between defining something and discussing the mechanisms that cause it.

    On page 4 of his book he talks about the modern theory of evolution in a way that confuses it with the history of life but then he goes on to define evolution.

    The first [component of evolutionary theory] is the idea of evolution itself. This simpley means that a species undergoes genetic change over time. That is, over many generations a species can evolve into something quite different, and those differences are based on changes in the DNA, which originate as mutations.

    I prefer to talk about populations evolving, rather than species but Coyne's definition of evolution is pretty good. I would say that evolution is a process where heritable changes take place in a population over time.

    Later on (page 13), he makes it clear that, "... processes other than natural selection can cause evolutionary change." In other words, he defines evolution as genetic change then discusses the processes that cause it (natural selection and random genetic drift). I prefer to call them mechanisms of evolution rather than "processes"—is that the source of your disagreement with me?

    Finally, on page 122, Coyne gets to a scientific definition of evolution when he says ...

    Let's take a brief digression here, because it's important to appreciate that natural selection isn't the only process of evolutionary change. Most biologists define evolution as a change in the proportion of alleles (different forms of a gene) in a population.

    Do you agree with Jerry Coyne and most biologists" or do you think you have a better definition of evolution?

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  18. Heleen says,

    As to the phenotypic plasticity in human height, this does not come under 'descent' as that is usually read in 'descent with modification'.

    The steady increase in the average height of Europeans over a period of 500 hundred years is clearly an example of descent with modification.

    Is it evolution? No, not according to my definition because it is not a genetic change. What I don't understand is how you distinguish between true evolution and non-genetic responses to the environment that shouldn't count as evolution.

    The second is a bottleneck effect in allele concent, and in the example negligeable as to evolution.

    Hmmm ... I think we may just have to agree to disagree. A great deal of evolution involves the founder effect. It's probably what gives rise to the pattern of punctuated equilibria, for example. If you dismiss those kind of events out of hand then we really can't have much of a conversation.

    BTW, I do not claim that the minimal definition of evolution is all there is to evolution.
     

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  19. It seems to me that you have a better grasp of what to do... largely starting "top-down" from the human history just tends to clog the issue with all sorts of resistance, based on all sort of other issues.

    As a specific example of what I think we need more of.... I have always been impressed with how effective a little video simulation I once saw was in getting good points across. The kids were "birds" and the touch screen video had a genetic "bugs" of different colors that were on different colored backgrounds for the "birds" were to try to eat. The very youngest kids were just having fun, but you could see the "light of understanding" turn on in their slightly older siblings. They really seemed to understand the key points. It seemed to me a nice, non-controversial way to introduce the foundational ideas of change. This then, over time, could enable kids to extrapolate out and connect to natural history of non-humans, and, then ultimately, to humans.

    Trying to do it just top down with a natural history over millions or billions of years, without the fundamental basics of what is actually happening at short periods of time in populations expects too much "faith" in science that some kids (well, mainly their parents) do not have. ...and ultimately has implications for humans that some people will not easily accept. I sort of think that early education should start from both ends, to some degree, but it should clearly have the "bottom-up" parts that operate at short time frames that will not have a lot of resistance and that go to the basic underlying mechanisms. Then kids--armed with real knowledge of mechanism--can make up their minds about evolution with the facts of process in hand, when they get a little bit older. But currently, the underlying processes of genome change are not usually part of any initial training whatsoever. (In part, because of the pitiful training that undergraduate education majors get in science education and, sad to say, training of many "molecular" biology science majors, as well.)

    It seems to me we have tried, since Darwin, to mainly just do "bottom-down" "long-ago" natural history from humans or animals over geological time, with quite poor results in US and some other places. Now that we can see evolution in laboratories for some bacteria, have good field examples, and can see huge number of examples of evolution at molecular genome levels and, lastly, understand proximate population genetics mechanisms so much better, can't we do better in educational results?

    As to related "fact and theory" ideas, I think a more complete version that should be advanced, is that 1) evolution is a fact, 2) evolution is a theory *and* (too often neglected in some contexts) 3) evolution is a process (genome change). All three are operative, it seems to me. Trying to have one or two without the others is like trying to use a stool with just one or two legs. I would, however, probably favor building the "process leg" first for younger students as it might make the construction of the other two easier.

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