A flawed argument
In May of 1993 one Ted Holden, crackpot extraordinaire, argued against evolution with the following bit of specious prose:
Trying to get from a non-flying creature to a bird that way, you would have at least one final non-flying stage, at which the wings were just about large enough to fly with, but not quite.The implication being, of course, that this hypothetical ancestor would never have made it, being burdened with large but useless wings. I responded with:
Folks, the old Tedster is trotting out one of the hoary chestnuts that are used to "refute" evolution, namely the "An incomplete organ is not adaptive" argument. Bales used to trot it out every so often. Like many another horse of another color, it's rather showy when you first trot it out, but when you put it through its paces it pulls up lame. It's a good argument; as that prolific essayist, Stephen Gould, is fond of pointing out, evolution does not select for future utility.
So if, as Ted is claiming, wings are of no value to an animal that can't fly, how did they evolve? It is beside the point to give chickens and the like as examples of animals with wings that don't fly -- these birds are recognizably the descendents of birds that could fly. There are at least four different issues involved -- the evolution of feathers, the evolution of flight feathers, the evolution of the wing limb, and the actual evolution of powered flight. In point of fact we have very little fossil evidence at this point, so any argument on the subject is largely speculative. However there is some data. Moreover the force of the objection lies in the claim that there is no path of advantage, so it suffices to show that the claim is false by showing a potential series of adaptations that offer advantage.
First of all, feathers. Feathers are an excellent insulator; they probably evolved from scales. It is notable that archaeopteryx (sp?) is anatomically very similar to a small dinosaur [coleosaurs, if I recall the spelling and the critter correctly.] Current theory has it that they were warm blooded, and could have used insulation.
However insulating feathers are a long way from flight feathers -- witness the hair like feathers of the ratites. We infer, therefore, that flight feathers imply an adaptation to flight. Now archie had flight feathers. So we would infer that archie could fly. Or could she? Archie was light boned, but she was still rather clunky for powered flight, and she lacked the supporting breast bone for attaching flight muscles. Frankly, I doubt that archie was capable of powered flight. However she would have been a pretty good glider. [I put no stock at all in Ostrom's insect herding theories.] She also had, if I am not mistaken, that useful claw that permits tree climbing.
So the sequence is: Feathers as a hair alternative for insulation in small predators. Invasion of the arboreal niche, ala squirrels. Gliding using feathers rather than a skin fold (unpowered flight.) Powered gliding. And finally, powered flight. By the bye, it should be noted that wings have functions other than flight. A wing is a very good offensive weapon. [Watch geese in operation some time.] It occurs to me that the original adaptive value for the musculature that powers wings in flight may have been to make the wing limb more effective as a weapon.
It is quite shocking to me that a dozen years have passed since I tossed off that "refutation". Since then there have been a number of finds of feathered dinosaurs.
This page was last updated July 1, 2005.