Friday, October 5, 2007

This Week's Citation Classic

The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme. S. J. Gould, R. C. Lewontin Proceedings of the Royal Society of London. Series B, Biological Sciences, Vol. 205, No. 1161, The Evolution of Adaptation by Natural Selection (Sep. 21, 1979), pp. 581-598.

I confess I am not a huge fan of Stephen Jay Gould. Although his extensive science writing is often charming, and has helped popularize evolutionary biology across a much broader spectrum (Wonderful Life was wonderful!), I consider much of his evolutionary thought simply wrong headed and strange. I won't go into specifics here, *cough, cough, punctuated equilibrium*, but some of his work is basically window dressing. I haven't read his latest opus, The Structure of Evolutionary Theory (its size, 5.1 pounds, is quite daunting; I'm waiting for the Reader's Digest version) so I could be wrong here, but I doubt it.

Dick Lewontin, on the other hand, is a great evolutionary biologist and has made many seminal contributions to the field.

Despite my misgivings about Gould, I found the paper on the Adaptationist Programme to be spot on. First off, it has a fantastic title. Not a cutesy punning title, but a novel, eye-catching title with side references and metaphors that actually make sense.

Second, the paper addressed a real concern in evolutionary biology. Despite G.C. Williams tour-de-force, Adapatation and Natural Selection, the study of adaptation in the '70s still suffered from wishy-washy, uncritical thinking (Larry Moran might argue still does today!). The problem was Just So stories (so named after the Kipling kiddie stories about How the Leopard Got His Spots etc.) where anyone can invent reasons, however fanciful, for why certain phenotypic traits exist.

Gould and Lewontin cite experimental work by D.P. Barash as an example of this problem.

Barash mounted a stuffed male near the nests of two pairs of bluebirds while the male was out foraging. He did this at the same nests on three occasions at ten-day intervals: the first before eggs were laid, the last two afterwards. He then counted aggressive approaches of the returning male toward the model and the female. At time one, aggression was high toward the model and lower toward females, but substantial in both nests. Aggression toward the model declined steadily for times two and three and plummeted to near zero toward females. Barash reasoned that this made evolutionary sense, since males would be more sensitive to intruders before eggs were laid than afterward (when they can have some confidence that their genes are inside). Having devised this plausible story, he considered his work as completed.

The explanation misses an obvious alternative. Perhaps the males approached the models a few times, learned that they were fake, and thereafter no longer responded to them. The proper way to conduct this experiment is to expose a male to the model once... either before or after the eggs are laid. The experiment was replicated by Morton et al. (1978) who found no evidence for anti-cuckoldry behavior.

Gould and Lewontin believed that too many biologists were simply making up similar stories for every conceivable trait. Perhaps some organismal traits have no function! Take the belly button. Maybe it evolved to collect lint so that cavemen would have a source of fiber for their diets! Uhhm... not likely. The belly button is an example what Gould and Lewontin would call a spandrel. The San Marco spandrels are so beautifully decorated with mosaics that one could be convinced that they were designed expressly to display mosaics. Not so! Spandrels simply hold up the ceiling; they were painted to make them look pretty. Belly buttons serve no function; they are simply the remnant of the umbilical connection between the mother and fetus.

So how should one determine whether a certain trait is an adaptation? A good adaptive hypothesis will make predictions concerning the trait it seeks to explain. Also several criteria should be met: (1) trait variation must affect fitness or a component of fitness; (2) the hypothesis of adaptive variation must be confirmed by either manipulating the selective environment or the phenotypic trait itself; and (3) the mechanistic link between the trait and fitness must be demonstrated.


  1. I attended a great conference dedicated to this paper a few years back. It is to this day one of the most important papers in all of biology, if anything, getting more and more important with time.

  2. The "Reader's Digest" version is available. It's the relevant chapter on Punk Eek from The Structure of Evolutionary Theory, and is simply entitled Punctuated Equilibrum.

  3. The Readers Digest version was not written by Gould, it was written by Wallace Arthur.

  4. For a quite alien perspecitve on this paper, people might be interested in the book called "Understanding Scientific Prose", by Jack Selzer. It's a collection of chapters by various 'Science Studies' scholars. These are people in the humanities who study how science works and what scientists do.

    In this book they've all taken the Spandrels paper as their object of study. They discuss the use of citations (nifty!), the role of gender (??), narration and modernity. They subject it to deconstruction, rhetorical analysis, and structural analysis (does this undo the deconstruction?). Altogether a very alien perspective.

    Amazon has it but for a high price - you can probably get it from your university library for free.

  5. "Take the belly button. Maybe it evolved to collect lint so that cavemen would have a source of fiber for their diets!"

    Nonsense. Belly button lint fibre is indigestible by human beings (it requires a capacious gut like that of a gorilla, which is therefor lintivorous). The belly button evolved so that cavemen would have a source of lint to use as tinder. Obviously, this means the belly button didn't evolve in humans until after we'd invented fire. This is confirmed by the fact no human belly button so far discovered pre-dates the discovery of fire.

  6. I love the line from the Amazon's review of Punctuated Equilibria: "It's a testimony to the density of the work that a single chapter is sufficient to make a complete and thorough book on its own. The publisher has simply cut away the first 745 pages and the last 318 of the original."

    Part of my reluctance to tackle TSOET is that it is so dense.

    Here's a quote from the Mark Ridley's NYT Book Review, "But there is no disguising that it is a heavyweight work. The style ranges from verbosity to almost pathological logorrhea."

    Barash also wrote a few choice lines about it in Human Nature Review 2002 Volume 2: 283-292, including: "billowing clouds of verbal flatulence", but you have to wonder about his objectivity.

    Maybe I will read Biased Embryos and Evolution instead. Understanding Scientific Prose sounds interesting too.

    Mike, you've captured Cretinist logic quite well...

  7. Since I have read The Brick, I felt no need to buy the PunkEek excerpt separately. But the rest of the book is most definitely not about PunkEek - it is about other areas which I find much more interesting than PunkEek, e.g., levels and units of selection, evo-devo, developmental constraints. I actually found the PunkEek section least interesting part of the book.

  8. I'll have to finish reading The Worderful Life one day. I have read the summary of Gould's argument on rapid evolution and I have been skeptical of this. I am more in favor of Richard Dawkins' explanations. I do have a lot respect for Gould.

  9. I agree that the punc.eq. part is the most boring of gould's fat book. But being his most paleontological, personal achievement, I forgive him.
    I just wander what indeed does John have against P. eq... what is so "terrible"?

  10. "Spandrels, like every text, can only be fully understood within its political-cultural context. In the case of Spandrels, the context was the attempted intellectual lynching of a young science, sociobiology, which at its most uppity claimed to account for human nature in ways that were distasteful to many, not the least those with Marxist inclinations." (Q. Rev. Biol. 70:485) The part about hypotheses is good, too.

  11. It's not that I disagree with Punk Eek, but rather that I think its importance is substantially exaggerated. The theory purported to solve a critical controversy; it did not. The gradualism v. saltationism conflict is terribly overblown. Moreover, the theory does not possess any great explanatory power, fails to make good predictions, and is basically a descriptive metaphor of the fossil record.

  12. What controversy are you talking about? P.eq. is not about saltationism vs. gradualism.
    And what do you mean, it "fails to make predictions"? There are many well-established facts that "fail to make predictions" or have great "explanatory power"

    P. Eq adresses the fact that species in the fossil record are observed to be for very long periods in stasis, whereas the periods of time in which new species originate are comparatively much shorter.

    I think stasis may not have "explanatory power" but ratherm it is a remarkable fact that opens important, profound questions.
    Stasis was truly neglected before Gould put it back on the table...
    Sadly, it STILL is neglected by many.