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The Origin of Avian Flight: Comparing Explanations from Darwinism and Intelligent Design

Microraptor gui holotype under UV light.jpg

As we noted yesterday, Illustra's new film Flight: The Genius of Birds had its big Southern California premiere over the weekend. Flight makes a case for intelligent design, but Darwinian evolutionists have not been without their own explanations. Here's a chance to compare the scientific merits of the competing views.

As a rule, a scientific explanation should avoid several common fallacies. One is the post-hoc fallacy: claiming that A caused B simply because A preceded B. Another fallacy is ad hoc reasoning: multiplying auxiliary hypotheses to maintain one's favored hypothesis. A third fallacy is begging the question. For instance, if an ID proponent were to state in a debate with an evolutionist about the origin of flight, "Because birds are designed, its flight systems must also have been designed," that would beg the question at issue. An even worse error is to ignore or arbitrarily "rule out of bounds" alternative explanations.

Some of the recent Darwinian accounts for the origin of flight commit all these fallacies. For instance, a news item from the University of Southampton is titled, "Dinosaur wind tunnel test provides new insight into the evolution of bird flight." This completely ignores all non-evolutionary explanations from the outset. All claims thereafter are doomed to beg the question of evolution.

In the article itself, we see the other fallacies fly by: one of the professors who put a model of the four-winged dinosaur Microraptor gui into a wind tunnel to test its aerodynamics committed several of the fallacies in these statements:

"Significant to the evolution of flight, we show that Microraptor did not require a sophisticated, 'modern' wing morphology to undertake effective glides, as the high-lift coefficient regime is less dependent upon detail of wing morphology."

"This is consistent with the fossil record, and also with the hypothesis that symmetric 'flight' feathers first evolved in dinosaurs for non-aerodynamic functions, later being adapted to form aerodynamically capable surfaces." (Emphasis added.)

But the issue at hand is the origin of powered flight, not just gliding. As shown so beautifully in the Flight film, true powered flight by any heavier-than-air vehicle (whether avian or artificial) requires a complex suite of interacting systems. The professor begs the question that gliding will evolve into powered flight. He commits the post-hoc fallacy by assuming that feathers "first evolved... for non-aerodynamic functions" then were later adapted for flight. And he commits ad hoc reasoning by invoking some unknown function for feathers in dinosaurs. (See also his team's paper in Nature Communications.)

What about those feathers on dinosaurs? Various "integumentary structures" have been found associated with fossils of some dinosaurs, but assuming they "evolved" into true flight feathers would commit the post-hoc fallacy again, besides begging the question that evolution "adapted" them for flight later.

Microraptor itself, with abundant feathers of modern aspect on four wings, is dated later than Archaeopteryx, a powered flyer. One fossil M. gui specimen was even found with a bird in its stomach, PNAS reported. Without getting into the weeds about fossils of feathers, since we want to compare explanations for the origin of powered flight, suffice it to say the record is confusing, even to Darwinian evolutionists, as Julia Clarke wrote in Science a few months ago:

Evidence is thus accruing for the function of early pinnate feathers in sexual selection, but there is little consensus on shifts in feather function associated with the evolution of flight. Reconstruction of ancestral conditions for the bird lineage requires consensus on the evolutionary relationships of key species. These species differ in feather shape as well as in their organization and layering on the forelimb and hind limb. Whether observed differences can presently speak to a gliding or flapping origin for flight is debated.

No wonder the film said that evolutionary theories about the origin of flight are highly controversial.

In its coverage of the Microraptor wind-tunnel experiment, New Scientist showed its propensity for ad-hoc reasoning: "plumage might not have evolved for flight but may instead have been a key aspect of sexual-selection displays."
More question-begging, alternative-ignoring, ad-hoc reasoning can be seen in a news item from the University of Oxford about bird tails. The article claims that shortened tails "gave early birds a leg up" in evolution -- "as soon as this happened it freed up their legs to evolve to become highly versatile and adaptable tools that opened up new ecological niches." Since this occurred after "birds had already evolved powered flight," though, it's irrelevant to the question of the origin of powered flight. It just shows the propensity by some evolutionists to beg questions and ignore alternatives.

Perhaps the most bizarre recent case of question-begging, ad-hoc reasoning is an item from McGill University with a Kipling-style just-so story title, "How birds got their wings." It basically claims that if you allow birds to evolve flight, they will:

This limb scaling changed, however, at the origin of birds, when both the forelimbs and hind limbs underwent a dramatic decoupling from body size. This change may have been critical in allowing early birds to evolve flight, and then to exploit the forest canopy, the authors conclude....

As forelimbs lengthened, they became long enough to serve as an airfoil, allowing for the evolution of powered flight....

Our findings suggest that the limb lengths of birds had to be dissociated from general body size before they could radiate so successfully. It may be that this fact is what allowed them to become more than just another lineage of maniraptorans and led them to expand to the wide range of limb shapes and sizes present in today's birds.

Needless to say, this explanation is unsatisfying. If changing limb ratios is all it takes to "allow" animals to fly, why didn't pigs try that? What "allowed" the simultaneous changes to the avian lung, flight feathers, and navigation? Why did the bones become hollow? How were the digestive, muscular, and respiratory systems overhauled, and how did they have any fitness value before powered flight emerged?

The ID Alternative

In Flight, Paul Nelson seeks the "vera causa" (true cause) of avian flight.

Now in the case of the origin of flight, we have a complex function, with all the associated anatomy and behavior and so forth, and the question we really should be asking is, what is the cause that is sufficient to bring this about? What is the vera causa of avian flight?

Nelson, Tim Standish and Ann Gauger consider the alternative of evolution or any other explanation that requires naturalism, resulting in just the "appearance of design" without actual design. Then they review all the systems that make flight possible, from feathers to "the most efficient respiratory system in the animal kingdom." Standish says:

Obviously, you're coordinating many, many, many different systems that have to be all exactly right for the bird to fly. And the more systems and component parts that are involved, the more challenging it is to explain how all of them came together so precisely in a bird.

Here's how Nelson sums up the ID explanation:

Here's the bottom line. You look at the anatomy of a bird, its behavior, its metabolism, the structure of its feathers, the structure of its muscles and so forth -- these are multiple independent points in a complex space, out of which flight emerges. And I think from a biological standpoint, to fly at all requires a cause that is able to visualize a distant functional endpoint, and bring together necessary to achieve that endpoint. Uniquely, and universally in our experience, only intelligence is capable of that kind of causal process.

Standish adds:

An engineered system is the product of a mind that anticipated a problem and figured out a multi-step way of addressing that problem. In birds you see exactly that kind of process. I believe intelligent design is the best explanation for avian flight, because it's the best explanation for every other kind of flight that we see. So why would I suddenly change the rules when I go from a 747 to a pigeon? ... They're engineering marvels. They're works of art. We know where engineered things come from. We know where works of art come from. So why would we attribute a bird to anything other than intelligence or mind?

The ID explanation, therefore, rests on known causes from our uniform experience. An explanation that avoids ad-hoc reasoning, the post-hoc fallacy, and question-begging arguments -- one that explores rather than ignores alternatives -- one that seeks the vera causa from known causes sufficient to bring about a phenomenon -- that explanation should be the one judged scientifically the best.

Image: Microraptor gui holotype under UV light/Wikipedia.