The 2012 Edge question, and a note on green sea turtles

November 10, 2012 • 9:56 am

“In his 1930 text The Principles of Quantum Mechanics, Paul Dirac, a colleague of Heisenberg, contrasted the Newtonian world and the Quantum one: ‘It has become increasingly evident… that nature works on a different plan. Her fundamental laws do not govern the world as it appears in our mental picture in any direct way, but instead they control a substratum of which we cannot form a mental picture without introducing irrelevancies.’

There was a world before Heisenberg and his Inexactness principle. There is a world after Heisenberg. They are the same world but they are different.”  —Satyajit Das, in his Edge answer

Every year literary agent John Brockman, who specializes in science authors, sets those authors—and other thinkers he knows—a provocative question, one often concocted by Steve Pinker.  We’re then supposed to write short answers, which John publishes on his Edge website and then collects in a book.

This year the question was “What is your favorite deep, elegant, or beautiful explanation?” This again came from Pinker, and it’s a nice one, for most of the answers (at the link) are really thought-provoking and good. (There are few exceptions, which I’ll leave you to find yourself.) It will repay your time to read the answers beneath the titles that intrigue you.

Though John is my agent, I’ve once again been derelict in failing to contribute, perhaps intimidated by all the neuronal power on display. Below are a few answers I especially liked, but have a look at them all. There are 192 of them: a real cerebral salon! (Just do a search on the Edge page to find anyone). Quantum mechanics and evolution dominated this year—no surprise given their explanatory power.  I’ve highlighted the ones below because they appeal to my personal tastes. Yours will probably differ.

Andrei Linde: “Why is our universe comprehensible?”

Anthony Garrett Lisi: “An explanation of fundamental particle physics that doesn’t exist yet”

John McWhorter: “How do you get from a lobster to a cat?”

Timmo Hannay: “Feynman’s lifeguard”

Seth Lloyd: “The true rotational symmetry of space”

Gregory Benford: “Beautiful, unreasonable mathematics”

Karl Sabbagh: “The Oklo Pyramid”

Gerald Smallberg: “The wizard of I”

Alvy Ray Smith: “Why do movies move?”

Marcel Kinsbourne: “How to have a good idea”

Richard Dawkins: “Redundancy reduction and pattern recognition”

Elizabeth Dunn: “Why we feel pressed for time”

Todd C. Saktor: “The elementary particle of memory”

Freeman Dyson:”Explaining how two systems of this world can both be true”

Shing-tung Yau: “A sphere” (I share his dilemma)

Leonard Susskind: “Boltzmann’s explanation of the second law of thermodynamics”

Lawrence Krauss: “The 19th century explanation of the remarkable connection between electricity and magnetism”

Tor Nørretranders: “The production of antibodies”
Steven Pinker: “Evolutionary genetics explains the conflicts of human social life”.  This is a spirited defense of evolutionary psychology, and you should read it even if you’re an EP opponent.
Peter Wolt: “The mysterious coherence between fundamental physics and mathematics”
Jared Diamond: “The origins of biological electricity”

Finally, although I knew the tale told by Dan Dennett in his answer: “Why some sea turtles migrate,” many readers might not be familiar with his example, so I’m recounting his answer in full. Note that Dan’s facts about the turtles appear incorrect, but the lesson is still useful:

Why Some Sea Turtles Migrate   

My choice is an explanation that delights me. It may be true and may be false—I don’t know, but probably somebody who reads Edge will be able to say, authoritatively, with suitable references. [JAC: I oblige Dan below.] I am eager to find out. I was told some years ago that the reason why some species of sea turtles migrate all the way across the South Atlantic to lay their eggs on the east coast of South America after mating on the west coast of Africa is that when the behavior started, Gondwanaland was just beginning to break apart (that would be between 130 and 110 million years ago), and these turtles were just swimming across the narrow strait to lay their eggs. Each year the swim was a little longer—maybe an inch or so—but who could notice that? Eventually they were crossing the ocean to lay their eggs, having no idea, of course, why they would do such an extravagant thing.

What is delicious about this example is that it vividly illustrates several important evolutionary themes: the staggering power over millions of years of change so gradual it is essentially unnoticeable, the cluelessness of much animal behavior, even when it is adaptive, and of course the eye-opening perspective that evolution by natural selection can offer to the imagination of the curious naturalist. It also demonstrates either the way evolutionary hypotheses can be roundly refuted by discoverable facts (if it is refuted) or the way those hypotheses can be supported by further evidence (if in fact it is so supported).

An attractive hypothesis, such as this, is the beginning, not the end, of the inquiry. Critics often deride evolutionary hypotheses about prehistoric events as “just-so stories,” but as a blanket condemnation this charge should be rejected out of hand. Thousands of such hypotheses—first dreamt up on slender evidence—have been tested and confirmed beyond a reasonable doubt. Thousands of others have been tested and disconfirmed.  They were just-so stories until they weren’t, in other words. That’s the way science advances.

I have noticed that there is a pattern in the use of the “just-so story” charge: with almost no exceptions it is applied to hypotheses about human evolution. Nobody seems to object that we can’t know enough about the selective environment leading to whales or flowers for us to hold forth so confidently about how and why whales and flowers evolved as they did.  So my rule of thumb is: if you see the “just-so story” epithet hurled, look for a political motive. You’ll almost always find one. While it is no doubt true that some evolutionary psychologists have advanced hypotheses about human evolution for which there is still only slender supporting evidence, and while it is also no doubt true that some evolutionary psychologists have been less than diligent in seeking further evidence to confirm or disconfirm their favorite hypotheses, this is at most a criticism of the thoroughness of some researchers in the field, not a condemnation of their method or their hypotheses. The same could be said about many other topics in evolutionary biology.

I think Dan’s referring here to the story published by Bowen, Meylan, and Avise in Proceedings of the National Academy of Sciences in 1989 (reference below, download free). Sadly, that paper appears to disprove the facts and explanation stated by Dan above.

Individuals from one colony of green sea turtles (Chelonia mydas) feed on the coast of Brazil, but nest not in Africa, but on Ascension Island, in the south-central Atlantic 2000 km (ca. 1300 miles) from the feeding grounds. How this happened was originally suggested by Carr and Coleman in 1974 (reference below, at link). They noted that as Africa and South America spread apart, a series of islands formed at the mid-Atlantic ridge where sea-floor spreading occurred, driving the continents apart. As the sea-floor spread, the new islands eroded beneath the sea, but new ones formed on the ridge as Africa and Brazil moved farther and farther away.

Carr and Colman suggested that turtles were originally breeding on the coast of northern South America and feeding offshore, and some of them originally found their way to a newly-formed volcanic island in the narrow channel between Africa and South America, nesting on the isolated beaches there. As that island eroded, they moved a bit farther away from South America to a newer island, and so on and so on, to island after eroding island, until they were breeding thousands of kilometers from where they fed.

They added that the turtles were genetically imprinted on the migration route, which kept them heading in the same direction to breed for millions of years. It’s a nice story.

But this beautiful theory was killed by an ugly fact: Bowen et al.’s PNAS paper showed that while natal homing is suggested among present-day colonies by fixed differences in DNA sequences of turtles from different rookeries, the divergence in DNA sequence between the Ascension rookery and other Atlantic rookeries is nowhere near as large as that expected had the Ascension turtle been isolated for millions of years. Bowen et al. suggest, in fact, that the colonization of Ascension is far more recent, and homing behavior is not genetically programmed but learned from environmental cues.

Why the descendants of those colonists go so far to feed is, of course, another question, though those might be the closest feeding grounds.

Perhaps Dan is referring to some other migration route, but I’m pretty sure that this is the story he’s recounting, and I’m not aware of any turtle that migrates all the way across the Atlantic Ocean.

Here, from Aimo Through the Years, is a female turtle on Ascension dragging herself back to the ocean after laying her eggs in the sand. (I’ve seen this in Costa Rica, and it’s a painfully slow process.) It’s impossible to watch the entire operation without feeling empathy for these beautiful animals.  Females even appear to be crying as they oviposit, exuding liquid from their eyes to keep the sand out.

Here, from Kelso’s Corner, is Ascension Island on the mid-Atlantic ridge:

h/t: Ben Goren for directing me to the Edge question site


Bowen, B. W., A. B. Meylan, and J. C. Avise. 1989.  An odyssey of the green sea turtle: Ascension Island revisited. Proc Natl Acad Sci U S A. 86: 573–576.

Carr, A. R. and P. J. Coleman. 1974.  Seafloor spreading and the odyssey of the green turtle. Nature 349:128-130

17 thoughts on “The 2012 Edge question, and a note on green sea turtles

  1. A fascinating collection! I find it interesting that some people think that wrong or bad ‘explanations’ are ‘beautiful’ or ‘elegant’. Not in my mental universe… Once shown to be wrong, for me an idea can at best be interesting, simple, clear, parsimonious… but never beautiful or elegant.

    1. Sadly, that paper appears to disprove the facts and explanation stated by Dan above.

      Apparently even our Jerry is susceptible to the occasional bout of sea turtle tears over the loss of a beautiful story!

      (Not snark. Dry humor. NOT SNARK! I love you man!)


      Thanks for linking me to a full morning’s worth of fascinating reading.

      1. Thank you Jerry (and John Brockman). I’m savoring them, one or two per day. I just let the idea-of-the-day slosh around in my brain for 24 hours or so.

  2. Regarding the turtle story, I heard a similar theory about eels. In other words, I heard that the reason eels (I think Europeans eels) migrate is because that’s how the behavior evolved because of the continental drift. It’s an amazing story but I’m not sure if it is correct.

    1. The story I read goes something like this: the same species of freshwater eel occurs in the rivers of eastern North America and Western Europe, and they’re catadromous (the opposite of salmon, e.g.) and migrate out to see to breed. The spawning grounds are in the Sargasso Sea, the relatively still centre of the North Atlantic Gyre. The progress and development of the larvae making their way back across the ocean has been described based on samples collected at various times, locations and depths, so we know they get there and swim up the rivers, but adults are much less numerous and their migration couldn’t be tracked. Europe’s much further away, and the possibility was suggested that it was just too far for non-feeding adults to make it; that would mean the European population would be reproductively futile, a useless byproduct of the viable American species. This

      I must have read it a long time ago, because G- Scholar tells me the European and American populations have been recognised as distinct species (Anguilla anguilla and A. rostrata) since at least the early 1980s, and there have been a lot of detailed studies since then.

  3. I had the privilege of watching and filming nesting behavior in Jupiter, Fl several years back. My Ph.D. advisor and his wife are nest watchers and knew just when to look. In fact, we saw *two* nesting that evening! Magnificent.

  4. OK only second one in, Richard H Thaler on “Commitment” has explained why hell is such a powerful meme. His example of Cocaine addicts writing a self incriminatory note publishable if they were found to have relapsed is the same psychology as those who emotionally commit to eternal damnation if they sin.

  5. Richard Dawkins is far too modest. His selfish gene explanation of natural selection is the most elegant and powerful, yet simple, explanation I learned in my life.

    1. I don’t think he decided not to pick the selfish gene explanation out of modesty, but rather the desire to promote other lesser-known beautiful explanations. I bet he has many more up his sleeve.

  6. As to the explanation put forward by Dan Dennett (wherever it originated), I hold (believe, whatever you want to call it) a similar theory for why eels migrate from Europe to the Sargasso Sea, and for why Emperor Penguins take that long march across the Antarctic.

    Can anybody shed light on how accurate these explanations are?

    1. The eel story takes passive advantage of the currents that have prevailed in the Atlantic for a long time. I don’t know that much vicariance is required to explain a pattern so closely tied to natural avenues of dispersal.
      Penguins have to walk far enough across the sea ice to reach a place that will still be there by the time they’re done. Again vicariance seems irrelevant, unless you think the sea ice has been increasing since penguins started breeding there.

  7. Females even appear to be crying as they oviposit, exuding liquid from their eyes to keep the sand out.

    I’m going to falsify Dan Dennett’s contention by leveling the ‘just-so story’ charge at that functional explanation of a decidedly non-human phenomenon.
    Sea-turtle tears (parodied by Lewis Carroll’s weepy Mock Turtle) are actually secretions of a specialized post-orbital salt gland, their chief means of excreting excess sodium and potassium. (Despite non-concentrating kidneys, they regulate their body fluids at a much lower concentration than their marine environment, which requires beaucoup energy and reflects their freshwater ancestry. Adaptation and constraint.)

  8. btw, thanks for linking the Bowen et al. article.

    It should be noted that they sampled only two Atlantic rookeries besides Ascension, both in the Northern hemisphere, and that their data are consistent with either recent colonization or relatively high recent levels of gene flow.
    I don’t think the ancient-colonization-and-gradual-lengthening-of-migration story is completely dead yet.

    (The question is not why they swim so far to the feeding grounds, where they live the majority of the year, but rather why they swim so far solely to reproduce. Because mating takes place close in space and time to the nesting beaches, males that hope to be successful have to swim all they way out there and back every year without ever even getting out of the water. All on account of these otherwise fully marine animals are stuck with laying an egg that has to incubate in air, reflecting their terrestrial ancestry that came after the freshwater ancestry. Adaptation and constraint.)

  9. My problem with “just so” stories is different from Dennetts. In practice they are isolated ad hocs and most often with no suggestion for testing. As such they are not even wrong, when formulated as hypotheses they are often wrong, and of course some will be correct.

    That doesn’t mean an area with only “just so” stories is fruitful or even correct. (Say, philosophy.)

    But – 192 answers? I hope it won’t take me a year before I’m finished!

    So far I’ve picked 3:

    – Linde is a conservative inflationist. In that way he is actually selling inflation short, yet he shows the power of the new cosmology.

    – Dyson is an inventive believer in belief. Nevertheless, I find his attempt of reconcilition between religion and science by proxy interesting since I have been entertaining the same hypothesis on the need for quantum gravity.

    Dyson’s gedanken experiment is probably sound, but I note that we have long observed gravitons (but only weakly constrained) by the spin down in pulsars.

    – Peter Woit is buffoon blogger with some technical competence. I hear he is teaching math in between handling student computer rooms, he hasn’t produced research for years and his only fame comes from (mostly irrelevant) non-physics based criticism of string theory.

    [His meltdown after LHC presented the putative Higg’s boson is spectacular, when caught out spreading rumors subverting the release process he claims some participating theoretical physicists are “arrogant”! (It is on Strassler’s blog.)

    Strassler: “As for knowing what you are talking about — well, that’s obvious, Peter. You know a lot, but unfortunately, not quite enough.”]

    It is a pity Brockman was taken in to give Woit another platform to speak his inanities from.

    Woit’s piece seems to be straight buffoonery along those lines. He is describing unitarity, necessary for complex matrixes describing probabilities to preserve total probability mass of 1. It reminds me of when Haught was describing addition in front of a room of professional mathematicians.

    1. I should note that I don’t know _if_ Dyson is trying to reconcile religion and science by laying the groundwork in physics. But I wouldn’t be surprised.

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