Sunday, February 27, 2011

Accelerated Human Evolution: Models and Data

I've prepared a bunch of exam questions for students in my molecular evolution course. I gave them out two weeks before the exam and I promised them that I would post some of these questions on my blog to see how you would answer them. I'm hoping that you, dear readers, will show my students that there really is some controversy.

Here's the fifth question.
In their 2007 paper Hawks et al. conclude,
The rate of adaptive evolution in human populations has indeed accelerated within the past 80,000 years. The results above demonstrate the extent of acceleration: the recent rate must be one or two orders of magnitude higher that the long-term rate to explain the genomewide pattern.
If the actual results demonstrate that human evolution has accelerated then why are there still scientists who dispute the conclusion?
The point of the question is the conflict between how scientists deal with data that conflicts with their model. In this case, it's scientists (like me) who are uncomfortable with the conclusions of Hawks et al. (2007). If the data they published is valid then this should be a situation where all scientists abandon their former models it light of a "nasty little fact."

But that never happens. Why?

I'd also like to discuss another topic. How many people who read the Hawks et al. paper are actually capable of evaluating the data to see if it supports the conclusions? Are we in a new age of biology where the complexity of the databases and the sophistication of the computer algorithms make it impossible for the average scientist to judge the quality of the experiments? How about reviewers, can they evaluate the methods and results?


Note: The issues get bound up with the adaptationist/pluralist debate because two of the authors on the paper published a book to promote their views. You can read some examples of the adaptationist views of Cochran and Harpending at: Examples of Accelerated Human Evolution. I don't think John Hawks supports such an adaptationist position but I'm hoping he will chime and tell us. (John is a really smart guy—on more than one occasion he has demonstrated that my arguments are full of holes. It's embarrassing.)

Another Note: Here are some blogs that you might enjoy reading if this question interests you.

Signals of recent positive selection in a worldwide sample of human populations…maybe

Signals of Positive Selection in Humans?

Overstating the obvious

SEED Reviews The 10,000 Year Explosion

Did biologists really think that human evolution stopped?

Are Humans Still Evolving?

John Hawks doesn't like random genetic drift

Genetic differences between human populations: more drift than selection?

Is Evolution Linked to Environmental Change?

Accelerated Human Evolution

Human evolution has accelerated

Are humans evolving faster?



Hawks, J., Wang, E.T., Cochran, G.M., Harpending, H.C., and Moyzis, R.K. (2007) Recent acceleration of human adaptive evolution. Proc. Natl. Acad. Sci. (USA) 104:20753-20758. Epub 2007 [PubMed] [DOI:10.1073/pnas.0707650104]

Hofer, T., Ray, N., Wegmann, D., and Excoffier, L. (2009) Large allele frequency differences between human continental groups are more likely to have occurred by drift during range expansions than by selection Annals of Human Genetics 73:95-108 [doi: 10.1111/j.1469-1809.2008.00489.x]

Pickrell, J.K., Coop, G., Novembre, J., Kudaravalli, S., Li, J.Z., Absher, D., Srinivasan, B.S., Barsh, G.S., Myers, R.M., Feldman, M.W., and Pritchard, J.K. (2009) Signals of recent positive selection in a worldwide sample of human populations. Genome Research 23 published in advance March 23, 2009 [DOI: 10.1101/gr.087577.108]

32 comments :

  1. But that never happens. Why?

    Models don't have to be exact replicas to be useful. An older familiar model that you have learned to use effectively could still be more useful to you than a newer more nearly exact model.

    It's a bit like preferring to keep using those comfortable well-worn shoes, rather than putting up with the discomfort of a new pair. And note that we still find Newton very useful, even though it has supposedly been superseded by Einstein.

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  2. I certainly know that many of the arguments are beyond the non-specialist layperson like me. This wasn't true even 25 years ago. But then at that time I was immersing myself in the literature -- including things I didn't know and therefore had to learn about as I read -- so it's hard for me to say how much that's a factor and how much is that the specializations are getting ever more specialized.

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  3. "I don't think John Hawks supports such an adaptationist position"

    Would you happen to be a betting man?

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  4. gcochran asks,

    Would you happen to be a betting man?

    Yes, but not on this topic. Here's what he said in a posting from last year [Richard Lewontin: "[T]oo rapid for genetic adaptation"]

    I don't really find the "pluralist versus adaptationist" debate very interesting. Despite the vocal complaints of some, I can't ever seem to locate the mythical "adaptationists" who deny that non-adaptive evolution ever happens. So the "debate" always comes down to whether particular adaptive hypotheses are true. Since no scientific hypothesis is true a priori, and since "those adaptationists are always saying stupid things" is not a scientific argument, I don't see the point.

    It's a typical adaptationist response to set up this strawman ("the mythical "adaptationists" who deny that non-adaptive evolution ever happens"). That makes me suspicious enough to avoid any bets.

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  5. You would have lost the bet. John liked our book: he reviewed it on his blog.

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  6. This discussion reads like it should be interesting, but I cannot for the life of me figure out what the argument is, if any.

    What, for example, is a 'pluralist' versus an 'adaptationist?' Is it anything like a 'selectionist' versus a 'neutralist?'


    Thanks, Henry Harpending

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  7. Larry-

    Does anyone else that you work with or know of share your perceptions of the way adaptationists conduct themselves?

    At times, it seem that you are grasping at straws to find someone whom you could call an adaptationist. Specifically, in your last comment on this post, you have moved from what "adaptationists" say about adaptation's role in evolution to what "adaptationists" say about adaptationism's role in the practice of evolutionary biology. Such shifting meanings of "adaptationist" begs the question of whether "adaptationists" as you perceive them actually exist.

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  8. Michael M says,

    Specifically, in your last comment on this post, you have moved from what "adaptationists" say about adaptation's role in evolution to what "adaptationists" say about adaptationism's role in the practice of evolutionary biology.

    Have you read the "Spandrel's" paper? It's always been about the practice of evolutionary biology and how you form hypotheses and address problems. That's why the original paper began its discussion of the adaptationist program with ...

    We wish to question a deeply engrained habit of thinking among students of evolution. We call it the adaptationist programme, or the Panglossian paradigm.

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  9. Henry Harpending asks,

    What, for example, is a 'pluralist' versus an 'adaptationist?' Is it anything like a 'selectionist' versus a 'neutralist?'

    An "adaptationist" is one who adheres to the adapationist program as described in the original Gould & Lewontin paper. They are similar to "selectionists" but I never heard of a "Selectionist Program" in evolutionary biology.

    A "pluralist" is one who actively entertains many different ways of explaining evolutionary problems. They might suggest, for example, that the presence of a particular character was due to fixation by random genetic drift.

    A "neutralist" is probably someone who accepts the idea that lots of alleles are neutral or nearly neutral. They are not the same as a true pluralist since a true pluralist is aware of the fact that beneficial alleles can be lost by random genetic drift and deleterious alleles can be fixed by random genetic drift.

    Pluralists are also more open to other mechanisms like mutationism, group selection, molecular drive, and species sorting.

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  10. The "Spandrels" paper is 32 years old and primarily a work of rhetoric and not evolutionary biology.

    Do you have anything more current?

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  11. @Cochran and Harpending,

    Do you still agree with this 2007 press release describing your earlier work.

    The new study comes from two of the same University of Utah scientists – Harpending and Cochran – who created a stir in 2005 when they published a study arguing that above-average intelligence in Ashkenazi Jews – those of northern European heritage – resulted from natural selection in medieval Europe, where they were pressured into jobs as financiers, traders, managers and tax collectors. Those who were smarter succeeded, grew wealthy and had bigger families to pass on their genes. Yet that intelligence also is linked to genetic diseases such as Tay-Sachs and Gaucher in Jews.

    Do you sand by the following statement and others in your book?

    We can confidently predict that many (perhaps most) as yet unexplained racial differences are also the product of recent selection. For example, we argue that the epicanthic eyelid found in the populations of northern Asia is most likely the product of strong and recent selection. (p. 18)

    That's a good example of the adaptationist program in action. Where does your "confidence" come from?

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  12. Unfortunately, this conversation always ends up with a "Where are these adaptioists?" conversation killer. I have met them, and here is one example. I'm deliberately keeping it vague to keep the persons unidentifiable.

    Someone was studying a mating strategy in a species. During the defense of the thesis, the candidate modeled the "optimal" behavior of this species. When the external examiner was questioning the candidate, they kept pressing on the question of why so many animals from the field study did not behave in this assumed optimal manner. To paraphrase the answer, the candidate asserted the organisms were simple behaving suboptimal, would be unfit, and this variation was sure to vanish from the population. The PhD supervisor smiled and nodded at this most excellent answer.

    The adaptionist program is alive and well, and very strong in some disciplines. It seems too often that the counter argument to Larry's discussion is to simple pull a "no true Scotsman" and ignore the point.

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  13. Michael M says,

    The "Spandrels" paper is 32 years old and primarily a work of rhetoric and not evolutionary biology.

    Do you have anything more current?


    It's interesting that the only people who ever say things like that are adaptationists. It's like they're determined to prove by example all the points Gould and Lewontin made in their classic paper.

    Let's test this hypothesis. Michael M, can you point me to a single example of non-adaptive evolution that you have publicly defended or promoted?

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  14. Moran asks "Do you still agree with this 2007 press release describing your earlier work."

    The press release says we published a paper "arguing that....", which is true enough. We still think the hypotheses ought to be tested, but the idea is too scary for most people. The whole thing BTW started as a test of the old workhorse bottleneck hypothesis of Ashenazi diseases: when a lot of marker data became available it was possible to test directly for signs of any diversity reduction at all in Ashkenazim. There was none, a finding confirmed since by SNP chips. Our selection model got tacked on but initially all the work was in the search for a bottleneck, which everyone ignored. So there is work on a neutral hypothesis for you, but it didn't work.

    Moran also asks "Do you stand by the following statement and others in your book?"

    Depends on what you mean by 'stand by'. We wouldn't bet the farm on any of the hypotheses we have in our book, but they aren't boring. The argument about race differences is just that the F statistic for the neutral genome is about 1/8: this has been well known since 1968. Things like skin color, IQ, others have F statistics pushing 80%, way outside the neutral range.

    Re adaptationism: I didn't realize you were citing Gould. Interesting diversity of cultures in this trade. My group of colleagues has always been population geneticists rather than biologists. Among 'my kind' Gould was always regarded as an amusing if sometimes annoying talker with no substance. I never read the Spandrels essay. I did read a paper of his in Evolution in the 1980s. His description of Wright's landscape model made me cringe with embarrassment for him.

    Don't know about Greg's reading of Gould.
    Best,

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  15. Henry Harpending says,

    The press release says we published a paper "arguing that....", which is true enough. We still think the hypotheses ought to be tested, but the idea is too scary for most people.

    Some would argue that there are several assumption that must be tested BEFORE you publish an adaptationist just-so story.

    What's the evidence that the intelligence of Ashkenazi Jews is significantly above that of neighboring non-Jewish citizens?

    What's the evidence that significant numbers of Ashkenazi Jews were "pressured into jobs as financiers, traders, managers and tax collectors" in medieval Europe? Most of the people in medieval Europe were farmers living on their own farms or in small villages. All the genealogy research that I've done shows that this was true of European Jews as well. (I've mostly been looking at the records for Poland and the Ukraine.)

    What's the evidence that wealthy medieval European Jews had "had bigger families to pass on their genes"? What percentage of Ashkenazi Jews have to be wealthy in order for your model to work?

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  16. Henry Harpending says,

    My group of colleagues has always been population geneticists rather than biologists. Among 'my kind' Gould was always regarded as an amusing if sometimes annoying talker with no substance. I never read the Spandrels essay.

    The other author of the Spandrel's paper was Richard Lewontin. He was a population geneticist.

    One of my favorite textbooks is Evolutionary Analysis, a population genetics textbook written by Scott Freeman and Jon Herron (I have the 1998 edition, the latest is 2007). Freeman and Herron devote an entire section to "The Adaptationist Program." Here's part of what this population genetics textbook says,

    Adaptations require explanations. One of the triumphs of Darwin's "On the Origin of Species" was that it provided an explanation for the existence of adaptations that was testable and that has survived testing. This explanation is, of course, evolution by natural selection. As we discussed in Chapter 5, the development of population genetics identified additional mechanisms of evolution. But none of these other mechanisms—mutation, migration, and genetic drift—can produce adaptation.

    ... Pursuit of the adapationist program requires caution (Gould and Lewontin 1979; Mayr 1983). It is not enough simply to devise a plausible hypothesis about what a trait is for and why it is adaptive. We must challenge the hypothesis by testing it to make predictions, and subject those predictions to test by collecting data.


    There seem to be two different sets of population geneticists. "Your kind" are different than the ones I know. Are "your kind" mostly anthropologists like you or physicists like Gregory Cochran?

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  17. "All the genealogy research that I've done shows that this was true of European Jews as well. "

    Where did you ever get the idea that many of the Ashkenazi were farmers anytime in the past thousand years? Because every history, every piece of data says that they were not. We have pretty good numbers for the early 20th Century:
    >
    >
    >
    > >From Kuznets (1960, p 1608)
    >
    > Distribution of Nonagricultural Labor Force
    >
    > Country Jewish Non-Jewish
    >
    > Poland (1931) 96% 47%
    > Soviet Union (1926) 96% 27%
    > United States (1940) 98% 82%
    > Latvia (1930) 99% 47%
    > Germany (1933) 99% 83%
    > Czechoslovakia (1930) 91% 73%
    > Hungary (1930) 97% 52%
    > Rumania (1930) 96% 37%
    > Bulgaria (1926) 99% 31%
    > Canada (1931) 99% 71%
    >
    >
    >
    >
    Further back in the past, even _fewer_ of the Ashkenazim farmed: essentially none. Those early-20th-century numbers are higher because of policy in some countries encouraging or even forcing Jewish farming, along with ideological-utopian experiments. Jews in the shtetls did not farm. I've read papers analyzing tax rolls for towns in the Polish-Lithuanian Commonwealth - _very_ few farmers. The only European Jewish group that seems to have farmed in those times were a few thousand Karaites in South-Eastern Poland.

    Main sources for my conclusion:
    _The Jews of Poland_, Bernard Weinryb. _A History of the Jewish People, Hayim Ben-Sasson. _Economic History of the Jews_, by Nachum Gross. _Aspects of Jewish Economic History_, Marcus Arkin. You might also look at this paper _From Farmers to Merchants_ (http://esnie.org/pdf/textes_2010/botticini-JEEA2007.pdf) by Maristella Botticini and Zvi Eckstein.

    white-collar specialization is _the_ characteristic pattern for Ashkeazni Jews over the last millennium.

    As for the increased fertility with income, there is of course plenty of evidence for that as well. It was a general pattern in premodern societies. I thought everybody knew that. Of course,. I also thought that everybody knew about the Ashkenazi Jews' unique occupational pattern and reproductive isolation and was familiar with the breeder's equation. Silly me.

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  18. Jim Crow thought our Ashkenazi paper was reasonable. What kind of population geneticist would you call him?

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  19. It's interesting that the only people who ever say things like that are adaptationists. It's like they're determined to prove by example all the points Gould and Lewontin made in their classic paper.

    It may be a "classic" paper, but it was written before most of the work on tests of neutrality was done. Simply claiming that, since a trait didn't need an adaptive explanation, no adaptive explanation need be sought was as shaky as claiming that, since the same trait could be explained adaptively, it had to be explained adaptively, especially in the absence of a method for making a quantitative measurement of the likelihood that the trait could be explained through gnenetic drift alone.

    Let's test this hypothesis. Michael M, can you point me to a single example of non-adaptive evolution that you have publicly defended or promoted?

    Maybe you should present an example of where publicly promoted or defended adaptationism.

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  20. gcochran says,

    Jews in the shtetls did not farm. I've read papers analyzing tax rolls for towns in the Polish-Lithuanian Commonwealth - _very_ few farmers. The only European Jewish group that seems to have farmed in those times were a few thousand Karaites in South-Eastern Poland.

    Okay. I stand corrected. Apparently in medieval times there were large regions of eastern Europe (Poland, Lithuania, Ukraine) populated by small Jewish villages (shtetls) where everyone worked at some sort of trade (e.g. making clothes or shoes). I assume the surrounding countryside was farmed by Christians who stayed out of the towns. Is that correct?

    white-collar specialization is _the_ characteristic pattern for Ashkeazni Jews over the last millennium.

    What sort of "white-collar" jobs made up the majority of the workforce in those small Jewish towns where most of the Ashkenazi Jews lived during the 12th-14th centuries?

    It's certainly true that by the beginning of the 20th century the Jews of eastern Europe were over-represented among doctors, retail business owners, and teachers.

    There were a lot working in factories, too. That's the group that was losing in the natural selection competition.

    As for the increased fertility with income, there is of course plenty of evidence for that as well. It was a general pattern in premodern societies. I thought everybody knew that.

    I'm certainly aware of the fact that it's a widespread belief. Do you have data showing that the average wealthy Ashkenazi Jewish family had more surviving children than the average poor Ashkenazi Jewish family? That's what is required in order to select for intelligence genes, right? Don't you have to have a lot of poor stupid families in order for that selection to work effectively?

    I was under the impression that the survival rates for children in cities was lower than that of children in farming communities. Was that a false impression?

    Of course,. I also thought that everybody knew about the Ashkenazi Jews' unique occupational pattern ...

    Some of my ignorance might be due to the fact that my knowledge of Ashkenazi Jews' unique occupational pattern is influenced by the history of those who ended up in New York city. Many of them weren't wealthy. They mostly lived in tenement houses in the Lower East Side.

    That must have been quite a shock for them since their above-average intelligence parents and grandparents must have mostly been wealthy "financiers, traders, managers and tax collectors" back in Poland.

    ... and reproductive isolation and was familiar with the breeder's equation. Silly me.

    The evidence for reproductive isolation is excellent but it doesn't explain your claim that there has been selection for above-average intelligence since medieval times.

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  21. Weinryb comments: "More children survived to adulthood in affluent families than in less
    affluent ones. A number of genealogies of business leaders, prominent rabbis, community
    leaders, and the like (generally belonging to the more affluent classes) show that such people
    often had four, six, sometimes even eight or nine children who reached adulthood. On the
    other hand, there are some indications that poorer families tended to be small ones. It
    should also be added that overcrowding, which favors epidemics was more prevalent among
    the poorer classes. In short, the number of children surviving among Polish Jews seems to have varied considerably from one social level to another."

    The bottom quarter or so of the Jewish population in the Polish-Lithuanian Commonwealth seems to have been poor enough to depend upon a kind of welfare paid for by the community. This had strings: Jewish communities often prohibited marriage among the poor.

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  22. Maybe you should present an example of where publicly promoted or defended adaptationism.

    I hit the "Submit" button instead of the "Preview" button.

    The italicized sentence should read:

    "Maybe you should present an example of where I publicly promoted or defended adaptationism."

    Doesn't publicly promoting or defending adaptationism, rather than failing to publicly promote or defending pluralism, make one an adaptationist?

    Hasn't Larry already presented an example of a person who is neither an adaptationist or a pluralist?

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  23. The job profile changed over time. For most of the time that Jews lived in Europe, they were fairly prosperous, more so than they were in 1850 Russian Poland.

    They didn't farm. For most of their time in Europe, very few were craftsmen. From 800-1700 or so, they almost all had white-collar jobs: moneylenders, merchants, estate managers, tax and toll farmers, etc. Mostly merchants at the very beginning, moneylenders in the High Middle Ages, more estate managers and
    such in the Polish-Lithuanian Commonwealth.

    Their population in Poland grew rapidly (from about 1% of the population in 1500 to about 10% in 1800) and they overflowed their niche - some began to work in crafts (lots of haberdashers and furriers), more in low-status retail jobs such as peddlers.

    In the High Middle Ages, something like 10% of the state budget in western Europe came from taxes on Jewish moneylenders. who were less than 1% of the population. When someone sacked a town, they went for the Jewish quarter first, for the same reason that Willie Sutton robbed banks.

    You have to be careful about projecting recent conditions into the past. I've had people tell me that high-medieval Jews were poor, when they were actually about as prosperous as the lower nobility. I've had other people try to tell me that Roman Jews in 100 AD were prosperous moneylenders, when they were nothing of the sort.

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  24. gcochran, this 'white collared specialization' your talking about is intriguing. I've read the basic premise, but all I know about your data set of rich Jews having more children than poor people is that it happened in premodern times.

    Do you think that any of this data may have been inaccurate? I'm curious, how did that data set handle orphans? Were they counted at all, or as part of the rich Jewish families that adopted them? Also, I've read that sometimes rich people don't always maintain monogamous relationships (Tiga Tiga Woods yall). How did this data set score it when a rich Jew had passion-child with a poorer mistress?

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  25. Larry writes:

    What's the evidence that significant numbers of Ashkenazi Jews were "pressured into jobs as financiers, traders, managers and tax collectors" in medieval Europe? Most of the people in medieval Europe were farmers living on their own farms or in small villages. All the genealogy research that I've done shows that this was true of European Jews as well. (I've mostly been looking at the records for Poland and the Ukraine.)

    From Wikipedia (granted, not exactly authoritative, but in line with other references I've seen):

    In the 17th century, almost no Jews lived in Western Europe. The relatively tolerant Poland had the largest Jewish population in Europe, but the calm situation for the Jews there ended when Polish and Lithuanian Jews were slaughtered in the hundreds of thousands by the cossacks during Chmielnicki uprising (1648) and by the Swedish wars (1655). Driven by these and other persecutions, Jews moved back to Western Europe in the 17th century. The last ban on Jews (by the English) was revoked in 1654, but periodic expulsions from individual cities still occurred, and Jews were often restricted from land ownership, or forced to live in ghettos.

    The foregoing fits with the other information I've seen in saying that legal strictures (prohibitions on land ownership, restriction to ghettos where there was insufficient space for farms) pressured Jews into occupations that could be carried out without land and within the high-density living situation of the ghettos. There was also the Christian prohibition on lending at interest (until Lorenzo de Medici figured a way around that), opening money-lending as a niche for Jews.

    I'm not at all sure this meant Ashkenazi Jews became substantially more wealthy than European Christians.

    For whatever combination of reasons, scholarship was prized among the vast majority of Jews I knew growing up, which served them well in the boomer generation, with its increasing emphasis on knowledge work. (When I was looking at colleges in the early 1970s, the statistics were that over 90% of Jewish kids of college age were attending college, while less than 45% of the total college-age U.S. population was doing so.)

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  26. Michael M says,

    Maybe you should present an example of where I publicly promoted or defended adaptationism.

    Okay, but first you have to tell me who you are.

    Doesn't publicly promoting or defending adaptationism, rather than failing to publicly promote or defending pluralism, make one an adaptationist?

    It's not either/or. Adaptationist thinking can be manifest in many ways. There are people here, for example, who may not have a public persona promoting adaptationism but their "skepticism" about anything non-adaptive suggests to me that pluralism is not an integral part of their worldview.

    Hasn't Larry already presented an example of a person who is neither an adaptationist or a pluralist?

    No. In this case you are either a pluralist or not. In theory, there can be several kinds of non-pluralist but there aren't too many Lamarckians or strict mutationists these days.

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  27. As much as I agree with you, Larry, that non-adaptive hypotheses need to be considered alongside adaptive hypotheses, your promotion of "Spandrels" as supporting you on neutral theory is a rather dazzling misreading of it. The whole idea of a "spandrel" as developed in the paper is one that relates to the favorability, if not out-right necessity, of a particular "trait" of an organism to the over-all layout of the organism. Thus, the existence of the "spandrel" is not in and of itself neutral. Rather, the proximate cause of the modifications to the "spandrel" which make it so fascinating to adaptationists bare little or no relation to the ultimate cause of the "spandrel" which is itself necessitated by the Bauplan of the organism.

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  28. Michael M says,

    As much as I agree with you, Larry, that non-adaptive hypotheses need to be considered alongside adaptive hypotheses, your promotion of "Spandrels" as supporting you on neutral theory is a rather dazzling misreading of it.

    I have never, ever, said that the Gould & Lewontin (1979) paper supports Neutral Theory.

    The Spandrels paper points out that there are many alternatives to adaptationist just-so stories and these alternatives need to be considered. Among the alternatives is evolution by random genetic drift but it's just one of many.

    I don't think I have ever in my life been confused about the difference between "Neutral Theory" and random genetic drift as a mechanism of evolution. Random genetic drift can result in fixation of nearly neutral OR deleterious allels and can also result in the loss of beneficial alleles.

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  29. Larry-

    Neutrality is a null hypothesis. All other hypotheses put forward in the "Spandrels" paper are alternative hypotheses, including the hypothesis that a trait is a "spandrel".

    Why is adaptationism "storytelling" while non-adaptive hypothesizing not?

    What makes adapative hypotheses somehow less legimtimate than non-adaptive hypotheses?

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  30. @ Michael M, parsimony.
    But all the hypotheses need to be "weighted" to find the most parsimonious one.
    There isn't a general rule that makes non adaptive hypotheses more parsimonious then adaptive ones...

    I would've liked to see a serious discussion, on this ground, in The "Null Hypothesis" in Evolution thread.

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  31. Michael M asks,

    Neutrality is a null hypothesis. All other hypotheses put forward in the "Spandrels" paper are alternative hypotheses, including the hypothesis that a trait is a "spandrel".

    That is correct. What's your point?

    Why is adaptationism "storytelling" while non-adaptive hypothesizing not?

    I imagine there can be examples of non-adaptationist "just-so" stories but I don't come across them very often.

    Most non-adaptationist explanations take into account the possibility of adaptation and try to explain why the non-adaptationist explanation is superior. That takes them out of the realm of "jut-so" stories.

    What makes adapative hypotheses somehow less legimtimate than non-adaptive hypotheses?

    Because you need to start with the null hypothesis (no adaptation) and your very first step should be to demonstrate that adaptation is involved. You are not doing good science if you arbitrarily skip that step.

    There's nothing wrong with adaptationist explanations based on proven adaptations. There's nothing wrong with adaptationist explanations that clearly begin with, "assuming that this is an adaptive trait."

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  32. That is correct. What's your point?

    That non-adaptationist alternative hypotheses are as much "storytelling" as adaptationist alternative hypotheses.

    I imagine there can be examples of non-adaptationist "just-so" stories but I don't come across them very often.

    You might try all of them.

    Most non-adaptationist explanations take into account the possibility of adaptation and try to explain why the non-adaptationist explanation is superior. That takes them out of the realm of "jut-so" stories.

    Just being able to come up with a non-adaptationist explanation doesn't make the non-adaptationist explanations superior.

    Because you need to start with the null hypothesis (no adaptation) and your very first step should be to demonstrate that adaptation is involved. You are not doing good science if you arbitrarily skip that step.

    The null hypothesis is not "no adaptation" but "no selection".

    There's nothing wrong with adaptationist explanations based on proven adaptations. There's nothing wrong with adaptationist explanations that clearly begin with, "assuming that this is an adaptive trait."

    The same goes for the explanation that a trait is a "spandrel" or that a "spandrel" is necessarily non-adaptive.

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