Thursday, December 17, 2009

Answering Creationist Claims (Part 1 - Birds Support Evolution)

“One of the best examples of evolution nonsense is the thought that a wingless bird began to evolve a wing. Why this would occur is not answered by evolutionists. The wing stub did not make the bird more adaptable to his environment. The first wing stubs would be much too small for the bird to fly. Why would a bird evolve wing stubs that are useless?…A bird with a useless wing is at a severe disadvantage…

…We are then led to believe that some birds got tired of carrying around a worthless half-size wing, so they grew fingers on the end to help climb trees. The wings became arms and a new species was developed.”

So here’s the first claim. Birds could not have evolved their wings, since a wing stub would've been useless. The creationist tries to tell us that a wing could not have evolved through evolution, for what is the use of half a wing? Yet this attempt is simply laughable.

Bird Wings came from Dinosaur Arms

The creationist makes 2 serious mistakes in the claim above. Wings did not evolve from wing stubs, and they did not evolve in to arms. They evolved from arms. According to current evidence, birds evolved from small theropods. This can be shown through the many similarities between the physiology and behaviours of birds & dinosaurs. In fact, the current fossil evidence shows quite a smooth transition from theropods to archaic birds to modern birds. Molecular evidence also puts crocodiles to be more closely related to birds than they are to lizards, turtles, snakes and other reptiles, which strongly supports the theory that birds evolved from dinosaurs, since dinosaurs and crocodiles share a common ancestor known as archosaurs. The wings of birds are evolved theropod arms.

Transition from Theropods to Modern Birds
From left to right: Compsognathus, Archaeopteryx, Gallus gallus(chicken).

Deinonychus Hand vs. Archaeopteyrx Hand
From left to right: Deinonychus Hand, Archaeopteryx Hand

Evolution of Dinosaurs
Birds are classified in the phylogenetic tree as dinosaurs.

OK, so we have now established that birds did evolve from dinosaurs. However, the creationist puts may ask: “But still, what is the use of a something halfway between a wing and an arm?” Don’t worry. Science has its answers.

Flight involves 4 physical forces (thrust and drag, lift and weight). For a bird to fly, many characteristics are required: feathers (improve aerodynamics), wings (create lift), hollow bones (increase structural strength), beaks replacing jaws (reduce weight) and so on. At first glance, this may give the look that since non-fully developed characteristics would've been useless, the Theory of Evolution has been determined false. It's not. Let's see how birds could've gained flight.

Flight evolutionary models

Archaeopteryx: The best example of a theropod-bird transition
Archaeopteryx, the earliest and most primitive bird known.

The Cursorial Model

This model states that flight evolved in running bipeds through a series of short jumps. As the length of the jumps extended, the wings were not only used for thrust but also for stability, and eventually eliminated the gliding intermediate. The model was then modified to describe the use of wings as an insect foraging mechanism which then evolved into a wing stroke. By running then jumping, less energy would've been used compared to only running. Combined with Archaeopteryx’s long and erect legs, supporters say that birds gained flight through jumping from the ground.

However, although this model sounds plausible, current evidence refutes it. Due to its weight, Archaeopteryx would need to run faster than birds by a factor of 3 to fly! Also, the heavier the bird, the longer it needs to run. For Archaeopteryx to fly, just guess how much energy it has to waste! Archaeopteryx’s ineffective aerodynamics also means that it could only fly for extremely limited times before falling! Thus, physics strongly disagree with this theory.

The Arboreal Model

The model states that Archaeopteryx was a reptilian bird that glided from tree to tree. After the leap, Archaeopteryx would then use its wings as a balancing mechanism. Archaeopteryx developed gliding to save energy according to the model. Although climbing trees may sound energy-wasting, the benefits are great. By gliding from tree to tree, Archaeopteryx would've conserved a lot more energy than staying on ground.

This model is supported by the fact that Archaeopteryx’s foot claws and hallux are very similar to those of modern perching(standing on branches) birds. This characteristics strongly support the view that Archaeopteryx was arboreal. Current tests have also shown that despite not having a supracoracoideus pulley system (SC), Archaeopteryx can still glide jumping from trees. It would've not been able to fly by running though.

However, a study suggested that the arboreal and cursorial model are not mutually exclusive, as many extant birds exhibit different degrees of ground- and tree-based behaviours. Instead, the study proposed that birds should be placed on a spectrum according to the extent of ground and/or tree foraging they exhibit.

The Pouncing Proavis Model

This hypothesis was first proposed by Garner, Taylor, and Thomas in 1999. This hypothesis is distinct from the hypotheses above in that it “proposes that locomotor control, rather than some direct attribute of flight such as speed or efficiency, was the selective pressure that initiated the evolution of fight in birds”. This hypothesis makes the claim that birds evolved from small predators that ambushed their prey from elevated positions. Over time, natural selection would favour those predators that had greater lift-based control, slowing turning the action from pouncing into swooping. Further selections for greater swooping ranges will then lead to flight.

The authors believed that this model is superior the previous models for these reasons:

The Mosaical evolution of Archaeopteryx

Both of the models are unable to explain why Archaeopteryx has a theropod-like skeleton and yet has a fully feathered wing, as they predict the co-evolution of the whole suite of skeletal and non-skeletal flight characteristics in birds. On the other hand, the Pouncing Proavis Model predicts the evolution of an Archaeopteryx-like grade of organization through continued selection for enhanced control of body position during a jump or controlled fall.

The Coexistence of Primitive Pouncers and More Advanced Fliers

Fossils of feathered dinosaurs were found in Late Jurassic and Early Cretaceous deposits, such as Sinosauropteryx, Caudipteryx, and Protoarchaeopteryx. Rahonavis, a dromaeosaur with bird-like characteristics were even found in the late Cretaceous! On the other hand, archaic birds such as Iberomesornis were found at the same period. This means that bird-like-dinosaurs and birds coexisted.

The arboreal and cursorial model predicts that as theropods became more adapted to flight, natural selection will eliminate theropods that did not show such abilities. But this is not the case. In contrast, the Pouncing Proavis Model predicts animals that started evolving Archaeopteryx-like features would have been selected for flight control instead of speed and agility. Gradually, however, natural selection pressures would begin selecting for improved flight efficiency, allowing those theropods to develop into a more bird-like niche. As pouncing bird-like dinosaurs and fully developed birds would not compete directly, they can coexist, and this matches the fossil record.

The primitive perfection of feathers

Both the arboreal and cursorial models proposes that feathers evolved under natural selection for increased life. However, it is hard to see how any feathers more primitive than modern feathers can generate enough lift. Instead, the Pouncing Proavis Model proposes that feathers were initially selected for increased drag, not lift, as this model proposes that the initial selection was for improved control during pouncing/swooping. Through continuous selection for increased drag and improved structural stability, feathers suitable for flight would evolve. This process of getting entirely new functions from existing systems is known as pre-adaptation.

Stages of feather evolution as outlined by Xu & Gou 2009
Diagram showing the stages of feather evolution as outlined by Xu & Gou 2009.

Successful Prediction of the Theropod-Bird Transition

The Pouncing Proavis model is consistent with the current evidence, whereas the arboreal and cursorial model are not. This model matches the currently observed sequences of character acquisition by theropods. For example, the Pouncing Proavis Model and the cursorial Model successfully predicts that Archaeopteryx is ground-dwelling; while the arboreal Model fails to do so. On the other hand, the arboreal and cursorial models proposes wrongly that weight reduction evolved parallel to an improvement in wing aerodynamics; however, the fact is that birds reduced weight after that, and the Pouncing Proavis model predicted is consistent with this finding.

Wing-assisted Running(WAIR) Model

Wing-assisted running is a recently discovered locomotor behaviour that allows birds to ‘run’ up obstacles(Dial, 2003). While such a task seems formidable for a biped, WAIR is used by ground-dwelling birds to escape from danger. Instead of supplying thrust in the direction of travel and lift to support body weight, the WAIR hypothesis suggests that the wings of ground birds serve to increase hind limb function and push the bird towards the substrate(the place they are running on), increasing traction. This is achieved through the simultaneous flapping of wings and running. The WAIR model have been documented in up to 4 species of ground birds.

So how does this explain the evolution of flight? When escaping from predators(perhaps when chasing prey?), protobirds that are able to use WAIR will have much higher odds of survival compared to ‘normal’ theropods, as they can reach elevated positions(cliffs, hills, trees, etc.) For protobirds to achieve this feat, the wing doesn’t need to be very big, but feathers are required. 3-day old hatchlings were documented to use their partial wings the run up steep inclines, while those with feathers removed could not.

There has been however research that disagrees with WAIR. It was found that the shoulder joint orientation in protobirds prevented the lifting of of the wing higher than the backbone, thus preventing flapping flight, and WAIR as well. (Senter, P. 2006)

Despite the importance of such a hypothesis in explaining the evolution of flight in birds, much remains unknown about the mechanics of WAIR, and work still needs to be done.

WAIR observed in modern birds.
Could this be how birds conquered the sky?


We have now refuted the creationist claim that birds cannot be evolved from earlier, transitional forms:

“The idea that birds or anything else has million-generation evolutionary plans is childish. The evolutionary concept of growing a wing over millions of generations violates the very foundation of evolution, natural selection.”

You’ll need to try harder, evolution-deniers.

But that's not all! In the same topic, further claims are made that no species are able to evolve into another species, aka fish-to-amphibian, amphibian-to-reptile, archosaurs-to-dinosaurs….. (with added insults). This is a common creationist claim, and I shall address it in the next post: Missing links? Wake up, creationists.

PS: There is this claim about how Cetiosaurus’s long neck disprove evolution. I would like to address this, but it’s not important in this series. Perhaps I will give a answer after this series.


Glen, C.L., and Bennett, M.B. (November 2007) (abstract page). Foraging modes of Mesozoic birds and non-avian theropods. 17.

Garner, J., G. Taylor, and A. Thomas. 1999. “On the origins of birds: the sequence of character acquisition in the evolution of avian flight.” The Royal Society. 266, 1259-1266.

Xu, X. and Guo, Y. (2009). The origin and early evolution of feathers: insights from recent paleontological and neontological data. Vertebrata PalAsiatica 47 (4): 311-329.

Matthew W. Bundle and Kenneth P. Dial. 2003. "Mechanics of wing-assisted incline running (WAIR).” The Journal of Experimental Biology. 206, 4553-4564"

Senter, P. 2006. Scapular orientation in theropods and basal birds, and the origin of flapping flight. Acta Palaeontologica Polonica 51 (2): 305–313.

Previous: Answering Creationist Claims (Introduction)

Next: Answering Creationist Claims (Part 2a: We Don’t Jumble Fossils Together)