“Your Inner Fish”– TV version– has begun

April 11, 2014 • 2:29 pm

by Greg Mayer

Jerry noted in February that friend-of-the-site Neil Shubin will be presenting a three-part series on PBS this month based on his bestselling Your Inner Fish. The series began this past Wednesday; I was unable to see the whole episode (because at the same time I was writing an exam I had to give the next morning!), but it seems to have gotten off to a good start, and I saw appearances in one or more of the clips not only by Neil, but by my friends and colleagues Steve Gatesy, Ted Daeschler, and the late Farish Jenkins (all of whom were involved in the discovery of Tiktaalik).

Neil Shbin holding a cast of Tiktaalik.
Neil Shubin holding a cast of Tiktaalik.

The program has a well done website, where you can watch full episodes, as well as many other videos, and find other great resources. There is a parallel website hosted by Biointeractive.org, an arm of the Howard Hughes Medical Institute, which also has many resources. The two sites seem to be only partially overlapping, so it’s worth visiting both.

The second episode will be aired in most areas next Wednesday, April 16, and the third episode the week after (April 23), but show times and dates may vary locally. There are also several re-broadcasts, and episodes become available on the website after broadcast. A DVD version will be released later this spring.

Tiktaalik had hind limbs!

January 14, 2014 • 9:46 am

by Greg Mayer

In a paper in press in the Proceedings of the National Academy of Sciences, Neil Shubin, Ted Daeschler, and the late Farish Jenkins describe the pelvis and partial hind limb of Tiktaalik roseae, the lobe-finned fish from the Canadian high arctic that they discovered in 2004 and described in Nature in 2006. Tikataalik is a transitional form from fish to tetrapods, and presents such a suite of advanced (for a fish) features that Neil dubbed it the “fishapod”. The newly reported finds show that Tiktaalik had a very substantial pelvic girdle and limb, which must have had a significant role in locomotion.

Of course, it’s not a surprise that Tiktaalik had hind limbs– most vertebrates do– but  the nature of the hind limbs in this, the most tetrapod-like of fish, is of especial interest. It’s been known for a while that Neil et al. had found the hind limb, and their publication on it has been eagerly awaited. The most important find, a pelvis and part of the associated limb, was actually found on the original holotype specimen (the one from which the species was described) found in 2004; four other isolated pelvises were found in later years. Since the first publication, preparator Fred Mullison has been working to free all the bones from the encasing rock.

Comparison of the girdles of Tiktaalik to those of Eusthenopteron  (a 'standard' lobe finned fish) and Acanthostega (one of the earliest known amphibians)
Comparison of the girdles of Tiktaalik to those of Eusthenopteron (a ‘standard’ lobe finned fish) and Acanthostega (one of the earliest known amphibians)

So, what have we found out? The pelvis is robust, with an ilium and pubis, and a large acetabulum for receiving what must have been a substantial femur. There’s no ischium (the third bone in a typical tetrapod pelvis). The Tiktaalik website has 3D scans of the pelvis which you can rotate to see the full morphology.

Tiktaalik pelvis from below: ilium on left, the rounded acetabulum for reception of the head of the femur, pubis on right.  The pubis is directed laterally.
Tiktaalik pelvis from below: ilium on left, the rounded acetabulum for reception of the head of the femur, pubis on right. The pubis is directed medially.

Only a portion of the hind limb was preserved: the intermedium, two radials, and several bony fin rays (lepidotrichia). We can tell from the acetabulum though that the femur must have been robust.

Hind limb of Tiktaalik from Shubin et al. 2014. The thin rays are lepidotrichia; the upper rectangular bone is the intermedium, the lower pair are radials.
Hind limb of Tiktaalik from Shubin et al. 2014. The thin rays are lepidotrichia; the upper rectangular bone is the intermedium, the lower pair are radials.

Here’s how the team summarized their findings:

Although no femur was found, Tiktaalik‘s fin rays and several other bones suggest the hind fin was comparable in size and complexity to the front fin. The shape and size of the hip socket reveal that the fin was capable of a wide range of movements, from swimming to supporting weight and rotating more like a tetrapod limb. But the overall structure of the pelvis is still more fish-like. Whereas tetrapods have a pelvis made of three parts, Tiktaalik‘s pelvis is still made of one, like fish. …

Overall, the mix of fish and tetrapod characteristics show us that the structures and mechanisms necessary for the invasion of vertebrate life on land evolved in the water first. Not only that, but before this discovery, we thought the front fins held the key to how vertebrates began to walk on land. The “front wheel drive” theory that fish dragged themselves out of the water with strong front fins and puny hind fins no longer holds. It appears that an “all-wheel” or even a “rear-wheel drive” system is a more appropriate analogy as the hind fins were just as important and may have even been involved in a walking behavior first.

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Shubin, N.H., E.B. Daeschler and F.A. Jenkins, Jr. 2014. Pelvic girdle and fin of Tiktaalik roseae. Proceedings of the National Academy of Sciences in press. pdf

First two Images from the Tiktaalik website 2014 New Discovery page.

New books on evolution and vertebrates

November 27, 2010 • 10:29 pm

by Greg Mayer

Three new (or newish) books have come my way that may be of interest to WEIT readers.

First, my friend and colleague Jonathan Losos has edited a collection of essays entitled In the Light of Evolution: Essays from the Laboratory and Field. I’d mentioned his book about the world’s best animals, anoles, in a post last year. The new book features mostly chapters by scientists about the actual experience of carrying out research, and why they think it’s cool (NB: it doesn’t involve rock stars). Ted Daeschler and Neil Shubin, for example, relate their motivation and experiences in traveling to the Canadian Arctic in search of transitional tetrapods.  It’s aimed at a general reader or student audience, and thus might be of interest to a number of our non-specialist readers. I haven’t finished reading it yet, and hope to give a more complete report during Jerry’s next peregrination.

I’ve also just received a copy of How Vertebrates Left the Water by Michel Laurin, a famed Canadian paleontologist at the Muséum National d’Histoire Naturelle in Paris. The book is largely a translation (by Laurin himself) of his earlier Systématique, Paléontologie et Biologie Évolutive Moderne: l’exemple de la sortie des eaux chez les vertébrés (Ellipses éditions, Paris, 2008), with the text and bibliography updated. The book covers a lot of the same (muddy) ground that Neil Shubin’s Your Inner Fish does, although at a somewhat more technical and narrower level (sorry– couldn’t resist the allusion to coming ashore!).

And finally, not so new, is Bob Carroll‘s The Rise of the Amphibians, published in 2009, and which I got a copy of last year. Carroll is the dean of North American paleontology, and Laurin studied with him at McGill. Carroll’s book covers all of amphibian history, from their origins (the focus of Laurin’s book) to today. Although it has a predictably strong emphasis on the fossil record, he even includes a chapter on the  amphibian conservation crisis of today. Because reptiles (amniotes) descend from amphibians, this transition is covered as well. This book is the least likely of the three for casual bedtime reading, but it is well written, profusely illustrated, and has 16 attractive color plates.

Your ear bones came from your jaws

October 15, 2009 • 6:22 am

by Greg Mayer

Although the mammals and reptiles most people know are quite distinct– mammals are hairy, warm-blooded, live-bearers, that suckle their young, while reptiles are scaly, cold-blooded, egg-layers– a wider knowledge of the modern forms reveals that the differences are less absolute. There are many live-bearing reptiles, for example, and platypuses and echidnas lay eggs and are nipple-less. And it has long been known that mammals are descended from a particular group of fossil reptiles:  both the great British anatomist Richard Owen and the American paleontologist and zoologist Edward Drinker Cope noted this in the 1800s (Cope doing so in a paper with the wonderful title “The theromorphous Reptilia”, “theromorphous” meaning, roughly, “beast-shaped”).

Because the vertebrate fossil record consists mainly of bones, paleontologists need an osteological distinction between mammals and reptiles, and the definition of mammals is that our jaw joint is between the squamosal bone of the skull and the dentary bone of the lower jaw, while in reptiles the joint is between the quadrate and the articular.

Mammal and reptile jaw joints
Mammal and reptile jaw joints, from Wikipedia by Philcha

The stages in the picture above were about all that were known to Cope and Owen, but they could still see the connection between the groups. (The lower picture is of a pelycosaur, an early type of synapsid reptile, the synapsids being the group of reptiles from which mammals eventually evolved; Dimetrodon was a pelycosaur). Cope’s identification of early synapsids as the ancestors of mammals could be considered a prediction that intermediate forms would be found (I leave out Owen, because his views on evolution were equivocal). Later work has abundantly confirmed this, and the reptile-mammal transition is now probably the best documented of all higher level transitions in the vertebrates. A classic paper by A.W. ‘Fuzz’ Crompton and Farish Jenkins, teachers of mine from grad school, summarized the first 100 years of work on the subject.

Here’s a diagram of one of the intermediate forms. Note that it has a double jaw joint, and the bones in the lower jaw have become much smaller. If you look above to the mammal, you will see that these bones have become even smaller still, and detached from the lower jaw.

Double jaw joint
Double jaw joint from Wikipedia by Philcha. This figure is not quite right. The dentary/squamosal contact is actually much nearer to the quadrate/articular contact. The two joints are lateral and medial to one another, not anterior-posterior.

What has happened is that two bones of the lower jaw (the angular and the articular), and the quadrate of the upper jaw, of reptiles have become (some of) the ear bones of mammals– the tympanic, malleus, and incus, respectively (mammals have another ear bone, the stapes, which is the only ear bone in reptiles). This reduction in size and detachment from the jaw occurred in many gradual steps over many millions of years, all documented in the fossil record. Clifford Cuffey has a nice set of figures of some of these, and Karen Peterson of the University of Washington has posted class notes with some very nice figures. What makes this even neater is that the jaws themselves are derivatives of the anteriormost parts of the branchial (gill) arch skeleton, a subject I’ve mentioned before, and thus we can trace the history of these bones from the branchial apparatus to the ear by way of the mouth.

Just as Matthew was inspired to post about sponges after lecturing about them to one of his classes, I bring up the ear bones because I was lecturing to my vertebrate zoology class about the branchial skeleton and its derivatives this past Tuesday. It was also the very day that the New York Times had an article by Natalie Angier on the evolution of the mammalian ear bones inspired by a recent paper in Science (subscription required for full article) by Qiang Ji and collaborators. They describe the jaw of an early Cretaceous mammal that had a persistent reptile-like connection of the ear bones to the jaw.  The authors propose, quite reasonably, that this is a paedomorphic condition, that is, that it is the retention into the adult of an embryonic condition: mammalian embryos pass through a stage in which their jaw/ear bones resemble those of reptiles.

The working out of the history of these bones is one of the great triumphs of vertebrate comparative anatomy. Neil Shubin (sorry Jerry!) summarizes the highlights nicely in chap. 10 of Your Inner Fish.

WEIT review: Kevin Padian sucks me back into into the religion/science quagmire

April 1, 2009 • 7:06 am

Kevin Padian, a paleontologist at the University of California at Berkeley, has done pathbreaking work on the evolution of flight, and on other paleobiological issues.  He’s also been a stalwart defender of evolution against creationism, and is the president of the National Center for Science Education.

In the latest issue of Public Library of Science Biology (known as PLoS Biology), Padian has written a  review of Why Evolution is True.  I wish I could say I was pleased with it.  After all, Padian did start the review by praising the book:

First, make no mistake: this is a wonderful book, as far as the explanation of many of the interesting lines of evidence and case histories for evolution go. . . Coyne hits all the right notes, without over-dazzling the general reader with too many molecular complexities or obscure examples. This is a very readable, companionable work that takes its place alongside other fine recent explanations of evolution such as Evolution: What the Fossils Say and Why It Matters, by Donald R. Prothero [3], and Your Inner Fish, by Neil Shubin [4], as well as a great many Web sites that explain the evidence for evolution. It would be an excellent text for a freshman or non-majors course in evolution, or for a local book group.

So why am I grousing?  Because his review is not about the science — or even about the book. Rather, it’s about a book that he wanted me to write but that I didn’t.  Padian spends most of his review calling me to task for not emphasizing strongly enough that evolution is compatible with religious faith.

First, a scientific quibble.  Padian criticizes me for not using strict cladistic terminology:  we should not say, for instance, that amphibians evolved from fish because “fish” is a term reserved for an ancestor and all of its descendants — which is not strictly true because some descendants of early fish became amphibians, and, ultimately, reptiles, birds, and mammals. This is the same criticism that Eugenie Scott leveled at the book in her review in Nature (that’s no surprise, because Scott is executive director of the NCSE and a close associate of Padian).  I can see their point from a cladistic stand, but it’s not necessarily the best way to present evolution to the public.  Under cladistic terminology, no group could have evolved from any other group!  All of us (including Neil Shubin, the discoverer of  the transitional form Tiktaalik) call the aquatic, lobe-finned ancestors of tetrapods “fish”.   It’s common parlance, and not misleading to the public.  What would Padian call those lobe-finned ancestors?  At any rate, I don’t think using common parlance is a serious crime here; in fact, it makes things clearer.  So we can agree to differ on this (see the comments by Greg Mayer and Nick Matzke here).  But that’s not Padian’s main criticism.

Padian says that “truth” (as in the title of my book) “is a personal thing.”   And he complains that I have not explained to the readers what I mean by saying that something is “true”:

Based on the title of this book I would have expected a bit more engagement with the philosophy of knowledge. How do we know something is true, and what do we mean when we say something is true? What could make us abandon our claims, and realistically, would we ever do so?

But Kevin doesn’t seem to have noticed the following passage in the first chapter (page 16):

Because a theory is accepted as “true” only when its assertions and predictions are tested over and over again, and confirmed repeatedly, there is no one moment when a scientific theory becomes a scientific fact.  A theory becomes a fact (or a “truth”) when so much evidence has accumulated in its favor– and there is no decisive evidence against it– that all reasonable people will accept it.  This does not mean that a “true” theory will never be falsified. All scientific truth is provisional, subject to modification in light of new evidence. There is no alarm bell that goes off to tell scientists that they’ve finally hit on the ultimate, unchangeable truths about nature.  As we’ll see, it is possible that despite thousands of observations that support Darwinism, new data might show it to be wrong.

And on p. 222-223, at the end, I show why evolution qualifies as “true” under this definition, and also give examples of possible observations that could disprove evolution.

But his real point is the NCSE’s standing policy of courting religionists, as articulated by Eugenie Scott:  “This is not a problem that you can solve merely by throwing more science at it.”  You have to cater to believers.

Three points here:

1.  The Dover decision rested on throwing science at Judge Jones, not convincing him that you could believe in evolution and God, too.  You don’t have to be a believer to refute creationist claims or to show that they were inspired by religious belief.

2.  You can’t solve the problem without throwing science at it. That’s what I was trying to do. That’s what I was trained to do. So I’m trying to solve the part of the problem that I’m capable of addressing without hypocrisy.

3.  Twenty-five years of hard work by scientific organizations like the NAS and NCSE, involving pushing religion/science accommodationism, have had no perceptible effect in changing the public’s acceptance of evolution.  It stays at about 40-50%, no matter what. Yes, court cases are won, but minds don’t seem to be changed.  I have pondered this long and hard, and have concluded that these figures won’t budge much until the United States becomes, over what will be a long period, a more secular nation: much like the countries of western Europe.

What should I have written, according to Padian?  That “truth” is philosophical, not objective, and that we should recognize and respect the philosophical “truths” of the faithful:

Creationists—people who deny evolution because it conflicts with their religious precepts—often tell us that whether we accept a naturalistic or a supernatural explanation of the world around us is a philosophical choice: a belief. They’re not wrong. That first decision—what kind of “knowledge” is going to be privileged in your mind—is ultimately a question of belief, a leap of faith, a decision about truth, if you care to use the term at all. . . . .

. . . Coyne does a very good job in this book of presenting the actual evidence for evolution. He is less complete on the philosophy and methods that underlie science, particularly in specific disciplines. And one would have liked to see more
about dealing with people who are apprehensive about the “truth” of evolution.

But this is something I’m incapable of doing.  I can’t tell people that faith and science are compatible, because I don’t believe it, and I don’t want to be a hypocrite.  Nor do I want to pander to religion.  And I’m not so sure that it is a “philosophical” choice” or a “belief” “to “accept a naturalistic versus supernaturalistic explanation of the world around us.”  Is it a philosophical choice to take antibiotics when you have an infection, rather than calling on a shaman or Christian Scientist?  (I bet you do take antibiotics, Kevin–is that a philosophical choice?)  And is it a “philosophical choice” to say that AIDS results from drug-taking and a dissipated lifestyle rather than from a virus?  Is it a “philosophical choice” to believe that the world is 6,000 rather than 4.6 billion years old?  Well, if these are philosophical choices, one of them works and the other one doesn’t.

The postmodernist claim that accepting scientific rather than spiritual truths is simply a matter of taste is a claim of breathtaking inanity.  Science helps us understand the world — it works.  Religion can soothe us, but I don’t see it coughing up equivalent truths, nor have I heard a convincing argument for what “truths” faith presents to us, as opposed to those revealed by secular reason alone.  Somehow I can’t believe that in his heart Padian accepts this philosophical equivalence, but maybe I’m wrong.  What exactly is his position vis-a-vis the supernatural? Can cancer be cured by both shamans and chemotherapy? Is he perhaps saying that books defending evolution should go easy on those religious views from which he himself isn’t fully emancipated?

Finally, Padian makes the following statement:

All these are worthy and sensible statements. And yet Coyne begins his last chapter with the statement of an audience member to him after his public lecture: “I found your evidence for evolution very convincing—but I still don’t believe it.” Well, nothing says that our job is to convince people of the “truth” of evolution—I don’t think it’s my job—but we would like people to understand it.

This is a remarkable admission. Does it mean that The National Center for Science Education doesn’t care if Americans accept evolution?  All that money and work, just so people can understand a theory they reject?

Your Inner Fish. . . now in paperback

February 6, 2009 • 5:03 pm

book_0flat

My friend and colleague Neil Shubin’s book, Your Inner Fish, has just appeared in paperback, so here’s your chance to get it at a reduced price. Neil and I have had a friendly competition going between our books (his appeared a year earlier), but I’m actually quite proud of his achievement and its role in documenting human evolution. It’s an excellent and lively read, dealing with the signs of our ancestry that remain in the human body, and it also recounts the famous story of his discovery of Tiktaalik roseae, an important transitional form between lobe-finned fish and amphibians.

Neil has a website for his book, which you can find here, and you can purchase the book on Amazon by clicking here. Highly recommended, and a New York Times nonfiction bestseller.

I should note that the illustrations for both Neil’s book and mine were done by the same illustrator, the indefatigable Kapi Monoyios, who did the cover shown above.

Continue reading “Your Inner Fish. . . now in paperback”