What Use Is Half a Wing?
Ken Dial is at it again, trying to explain bird flight from the ground up with his own version of a Darwinian story (see 01/16/2003). The title of his paper in BioScience1 harks back to an old criticism of Darwin’s theory: “What use is half a wing?” Well, half a wing could be a half a stabilizer is the new answer. Outstretched proto-wings, according to Dial’s WAIR theory (Wing-Assisted Incline Running) helps chukar partridges keep their balance when running up slopes, presumably escaping predators who might otherwise interrupt their ability to pass on their genes. Maybe this provides insight into the development of full powered flight in the dim past:
As a rebuttal to Darwin’s (1859) explanation of the origin and diversification of life, St. George Jackson Mivart (1871) posed a challenge: “What use is half a wing?” With this simple question, Mivart challenged Darwin to explain the adaptive role of intermediate forms within an evolutionary continuum, prompting Darwin to expand on the concept of functional shifts within structural continuity (Gould 1985). This concept of transitional functional and structural stages is the basis for exaptation, an integral component of modern evolutionary theory (Gould and Vrba 1982). A response to Mivart’s question is that if the wing of a flying bird is a product of small, gradual structural changes, these transitional forms must have had some function during the evolution [sic] of powered flight.
Discussing the ground-up (cursorial) theory and tree-down (arboreal) theory, Dial finds fault with both. Watching partridge chicks run up ramps, his team measured the advantage of stubby wings in helping them maintain stability:
The most significant finding from this body of work is that developing ground birds employ their incipient wings, adorned with symmetrical feathers, to execute brief bouts of aerial flight (dorsoventral flapping) and to enhance hindlimb traction (anteroposterior flapping) as they negotiate threedimensional terrestrial environments….
Thus, not only does the ontogeny of WAIR demonstrate functionally adaptive intermediate stages or steps, it demonstrates an adaptive continuum between featherless forelimbs, protowings with symmetrical feathers, and derived wings with asymmetrical feathers and a complex wing stroke.
As for the arboreal theory, Dial notes that there are no intermediates between gliders and flappers. But on the other wing, “there are no known contemporary analogs of cursorial bipeds that use their forelimbs to run faster, to run and glide, or to swipe at or capture prey, assumptions proposed among various cursorial hypotheses.” He says that this debate presents a false dichotomy: “both hypotheses fail to provide the functional and incremental adaptive stages of forelimb evolution necessary to achieve the fully developed flapping mechanics observed among extant species…” So he came up with his WAIR hypothesis independently, yet it shares advantages of both positions. “The WAIR hypothesis is a testable and inclusive approach to explain the evolution of avian flight,” he crows, “and it appears to resolve the impasse created from a strict cursorial or arboreal position.” Not only that, his approach provides a model for explaining transitional forms in the fossil record: identifying analogs among extant forms.
Ascribing functional explanations to transitional forms without integrating the wealth of corroborating evidence from other subjects (life history, behavior, development, ecology, and the physical sciences) will only lead to endless “just so stories” about the history of life.
We suggest that incipiently feathered forelimbs of small, bipedal protobirds may have provided the same locomotor advantages for inclined running as are present in extant birds. Whether sprinting across an obstacle-filled terrain or up inclined or even vertical surfaces, whether being chased or chasing, an animal capable of employing WAIR experiences improved hindlimb traction. What appear to be partially developed wings of recently discovered theropod dinosaurs [sic] (e.g., Caudipteryx, Sinosauropteryx, Protarchaeopteryx, Rahonavis, Unenlagia, and others) have confused scientists: Were these wings used for running faster, for gliding, for protecting eggs and young in the nest, or for catching food, or were they simply vestiges of once functional wings? In a protobird [sic], WAIR-like behavior could have represented an intermediate stage in the development of flight-capable, aerodynamic wings.
The transition is thus explained: aerodynamic forces on the outstretched “half wings” increase hindlimb traction; and short vertical movements. Rudimentary aerial ascent and controlled descent, as observed with modern partridge chicks, might have taken off into powered flight in gradual stages. Therefore, “ontogenetic transformation observed in juvenile species exhibiting WAIR is a plausible behavioral and morphological pathway of adaptive incremental stages that might have been exhibited by the lineage of feathered, maniraptoran dinosaurs attaining powered flight,” he claims. But with Dial’s frequent use of words like might, could and may have, how this differs from a just-so story might be a matter of debate itself.
See also the Science Daily summary of this paper, with picture of Dial holding a chukar partridge.
1Ken Dial et al., “What Use Is Half a Wing in the Ecology and Evolution of Birds?” BioScience, Volume 56, Number 5, May 2006, pp. 437-445(9).
Same dumb ideas, and same criticisms three years ago still apply (see 12/22/2003). All this shows is that evolutionists remain touchy about the criticisms of just-so storytelling leveled at them, and are trying desperately to clear this bad reputation. Don’t be distracted by the charts, graphs, diagrams and drawings in the paper; these all pertain to living, flying birds – not dinosaurs. And don’t be distracted by the highfalutin-sounding term “Wing-assisted inclined running” as if inventing a phrase is going to make a case. This is like the joke about the teenager being told by his doctor his lethargy is simple laziness, to which he responds, “now give me the scientific name so I can tell my parents.”
The mark of just-so storytelling is coming up with a hand-waving explanation that cannot be tested. That is still the essence of Dial’s hypothesis despite his protests to the contrary. Sweep away the scientific mumbo-jumbo and visual aids, and the jargon, because it is an irrelevant display of bluffing. Forget the references to so-called feathered dinosaurs, because there were contemporary modern birds of these that already had powered flight, so the maniraptorans could not have been transitional forms. Forget also the references to chicks of modern birds, because they already have the genetic information for powered flight; he cannot work backwards from the evolved to the unevolved. And erase Dial’s own bravado about how much better his hypothesis is than others.
Instead, imagine the Geico gecko trying to evolve powered flight by running up inclines with its forearms stretched out. A few moment’s visualization will do wonders to put this matter to rest. There are so many vital, interconnected, required morphological changes that would be required for the Geico gecko to do more than leap a few inches off the ground, it is inconceivable that there would be enough lucky mutations able to converge on turning his descendents into Woody Woodpecker, let alone the Road Runner. Cartoonists might be able to draw the transitional forms, but evolution needs to wait for mutations, almost all of which are harmful or neutral. Feathers, lungs, bone changes, flight software – how many thousands of beneficial mutations do you want to wait for? They all have to arrive simultaneously. And does WAIR explain flight in insects, pterosaurs and bats? Like Wiley Coyote forever behind the Road Runner, Ken Dial remains far behind his prey, an evolutionary explanation for flight.
Except for a brief hand-wave to future research needed in homeobox genes and evo-devo, Dial’s explanation is completely lacking in a genetic mechanism for attaining the required information for powered flight. Rather, it has all the characteristics of a Lamarckian story: the giraffe needed a long neck to reach the leaves, and the gecko needed WAIR to escape the predator. Presumably, the gecko already had defenses that worked just fine; “What say, mate, like, we just set and chat about a better way to settle our differences, hey? How would you like to save a lot of money on your car insurance?”
Ken Dial’s only achievement was to exhibit Darwinist sensitivity to charges of storytelling, and to point out that all the other evolutionary explanations don’t work. For that, his funny pages will get a good chuckle from creationists.