Organization: Software Maintenance & Development Systems, Inc.
From: firstname.lastname@example.org (Richard Harter)
Reply-To: rh@ishmael.UUCP (Richard Harter)
In article <1993May23.email@example.com> firstname.lastname@example.org (Mark Isaak)
>In article <1082@fedfil.UUCP> news@fedfil.UUCP (news) writes:
>>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.
>That sounds like a pretty good description of chickens, the most
>common bird on the planet.
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.
Richard Harter: SMDS Inc. Net address: email@example.com Phone: 508-369-7398
US Mail: SMDS Inc., PO Box 555, Concord MA 01742. Fax: 508-369-8272