Do Chicks Tell Dinosaur Tales?

first_imgFor years, evolutionary biologists have battled over the origin of flight.  Did dinosaurs run along the ground and take off, or did they jump from trees?  The first idea is called the cursorial hypothesis; the latter, the arboreal hypothesis.  In 2003, Ken Dial [U Montana] had an idea: maybe watching partridge chicks could inform the debate.  This month his approach made the journal Nature.1    Dial’s team videotaped chukar partridges from hatching to adulthood, and noticed their flapping behavior.  As chicks, they hold out their undeveloped forelimbs and appear to use them as stabilizers when running up slopes and over obstacles.  By the time they have grown up, this behavior has “evolved” into full flapping flight.  The evolutionary history of flight unfolded before his eyes:Based on our results, we put forth an ontogenetic-transitional wing (OTW) hypothesis for the origin of flight.  The hypothesis posits that the transitional stages leading to the evolution of avian flight correspond both behaviourally and morphologically to the transitional stages observed in ontogenetic forms.  Specifically, from flightless hatchlings to flight-capable juveniles, many ground birds express a ‘transitional wing’ during development that is representative of evolutionary transitional forms.  Our experimental observations reveal that birds move their ‘proto-wings’, and their fully developed wings, through a stereotypic or fundamental kinematic pathway so that they may flap-run over obstacles, control descending flight and ultimately perform level flapping flight (Fig. 1).  The OTW hypothesis provides a simple adaptive argument for the evolution of flight and can be tested and observed in extant fledglings.  This hypothesis differs from other published accounts in that it is flap-based (in contrast to requiring a gliding precursor), involves an aerodynamically functional proto-wing, incorporates both the simultaneous and independent use of legs and wings and assumes that a fundamental wing-stroke (described herein) was established for aerodynamic function early in the bipedal ancestry leading to birds.This explanation, the team thinks, overcomes limitations in both previous hypotheses.  The cursorial hypothesis fails to explain why “no extant species uses its wings to run faster, to secure prey or run�glide.”  The arboreal hypothesis has to “assume a gliding form was prerequisite to flapping flight because half a wing would have no function, and that the flap-stroke appears too complex and thus relegated to the derived [i.e., flying] condition.”  The new OTW hypothesis overcomes these pitfalls, he claims, by finding functions all the way up from running with outstretched forelimbs to full “fledged” flight.  If this recaptures the evolution of flight, it answers the question, “what use is half a wing?”    Science news reporters took up this hypothesis with triumphant fanfares: “Secrets of bird flight revealed” (BBC News), “All in a flap: New evidence of how birds took to flight” (PhysOrg).    Is there any fossil support for the transition from running with outstretched forelimbs to flight?  The paper did not refer to any fossils directly: only to “extinct taxa, such as the recently discovered fossil forms possessing what is assumed to be ‘half a wing’ and long cursorial legs” – but a check of the references showed only the 2004 paper about tyrannosaurids with unidentified skin filaments (10/06/2004) which may in fact have been flayed collagen fibers, not feathers (01/09/2008), and a paper co-authored by Dial about Microraptor gui which appears to have been an odd bird capable of flight (see 03/27/2007).  The “long cursorial legs” referred to a year-2000 paper about Caudipteryx, now thought by many to be a flightless bird within the class Aves, not a dinosaur.  None of these fossils appears pertinent to their hypothesis.  One was a dinosaur in the T. rex family.  Obviously, T. rex did not use its diminutive forearms for stabilization or flight!  The other two were probably feathered birds already capable of powered flight.  In short, the paper provided no fossil support and was based entirely on the behavior of modern true birds during their development.  The so-called “ontogenetic transitional wing hypothesis” rests entirely, therefore, on a hunch that this behavior supplies indirect indications of a presumed evolutionary history.1.  Kenneth P. Dial, Brandon E. Jackson and Paolo Segre, “A fundamental avian wing-stroke provides a new perspective on the evolution of flight,” Nature advance online publication 23 January 2008, doi:10.1038/nature06517; Received 20 August 2007; Accepted 27 November 2007; Published online 23 January 2008.Ken Dial has been pushing this fictional plot for five years now.  Our comments about his highly-speculative and unsupportable hypothesis, which rated the “dumb” award, bear re-reading (01/16/2003, 12/22/2003, 05/01/2006).  He claims it is testable – but only on living birds that already have the genetics for flying.  This is absurd.  It amounts to nothing more than job security for storytellers (12/22/2003 commentary).  Instead of repenting in shame, now he has added the Haeckel fallacy to it (to be explained shortly).    Dr. Dial is apparently fond of chukars.  That’s fine.  If he wants to go hunting for them, or even videotape them to understand their wing function, great.  No problem.  But when he tries to weave an evolutionary tale about the ancestry of flight, he is way, way off scientific course.  He is flapping Icarus wings in Fantasyland.  Nothing like a little sunlight of scrutiny to melt them, sending his ideas crashing down.    Over a century ago, Darwin-worshiper Ernst Haeckel promoted a similar idea.  He thought the evolutionary history of animals was preserved in their embryonic development: a human embryo replayed its evolutionary history by going through a worm stage, a fish stage, and finally a mammal stage.  This was dubbed the “Recapitulation Theory” and later was exalted into a law of nature, the so-called Biogenetic Law, by Haeckel.  Darwin himself considered it the most powerful evidence of his theory.  So strong was Haeckel’s belief and commitment to Pope Charlie, he notoriously doctored embryo drawings to support his pet hoax.    Haeckel may have seemed the mild-mannered Jekyll, but his ideas led to a Hyde of terror.  The Recapitulation Theory led to all kinds of social mischief, as described in articles by ICR and AIG.  Scientific racism, Freudian psychology, and abortion trace their ancestry to Haeckel’s myth.  Today, it is almost completely discredited by scientists, even evolutionary biologists.  Why should an animal retain any genetic memory of presumed ancestors and play them out on an embryonic stage?  Stephen Jay Gould was appalled by the idea.  He dismantled the “biogenetic law” mercilessly in his books, announcing that it is, and should be defunct.  Dr. Keith Thompson (Yale) said it went extinct in the 1920s and, as a scientific theory, is dead as a doornail.    Someone needs to inform Dr. Dial that his revival of recapitulation theory is embarrassing.  How can a living bird weave tales about dinosaurs evolving flight?  The whole notion is crazy.  Does Dr. Dial not realize that chukar partridge chicks have DNA for flight in every cell of their bodies?  Regardless of how they get about before they grow strong enough to fly, how on earth can he presume to think that their behavior as chicks tells anything about some mythical evolutionary past?  Where are the fossils?  Where are the modern reptiles holding out their forelimbs in a series of transitions leading to powered flight?    This is not science; it’s divination.  When he looks into the crystal ball (the video screen) of chicks running up a ramp with forelimbs outstretched, the trance comes.  Visions appear in his mind.  He is transported mentally into a swamp 150 million years in the mythical past.  Behold!  A theropod stretches out its forelimbs and escapes the predator bearing down on him.  OK; cut, time out.  Turn off the video playback and turn the lights back on.  Unless a random genetic mutation in the dino’s gonads helped its offspring run faster with outstretched forelimbs, significantly faster enough to make the slower guys die off, he has concocted a Lamarckian tale.  This phony idea, which Dial has been preaching for five years at least, is Lamarckian, progressivist, and Haeckelian.  It’s against the neo-Darwinist official party line.    Why, then, is Nature giving this crackpot idea the time of day?  Here’s why: all’s fair in love and war, and policy notwithstanding, any weapons that can be used against creationists, even old duds and lies, are fair game.  This dud is dressed up in new jargon and fancy acronyms, but it won’t fly.  If you want a shekel for your Haeckel, Dr. Dial, no sale.  To sound convincing, rather than experiment with living birds that already have flight software, chase down some lizards until they take off into the air.  Go experiment on the Geico gecko and see if holding out his forelimbs will help him fly some car insurance policies.  Better yet, give up on evolutionary biology altogether.  Do something useful with your life, like hunting some chukar meat for dinner, or marketing your videotapes to showcase the beautiful design of wings in these handsome birds.  Then we will stop laughing.(Visited 21 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img

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