Feathers: Created or Evolved?
[Last Update: November 25, 1992]
ob Bales has been using the feather as an example of something apparently designed, and thus lending support to his position of creation. In my opinion, nothing could be further from the truth. Bob prompted me to investigate the feather issue, and I would like to share what I found.
For those of you not familiar with the terminology, a passage from Miller and Harley 1992 (references at end of article):
Contour feathers consist of a vane with its inner and outer webs, and a supportive shaft. Feather barbs branch off the shaft, and barbules branch off the barbs. Barbules of adjacent barbs overlap one another. The ends of barbules are locked together with hooklike hamuli. Interlocking barbs keep contour feathers firm and smooth.
In trying to understand this, I came up with an analogy: a weeping willow tree limb. The limb is the shaft, branches are the barbs, and leaves the barbules. If the leaves had hooks on the ends/sides, these would be the hamuli. When the feather is arranged normally (i.e. not mussed) the hamuli would be hooked from the tips of the leaves on one branch to the petioles of the leaves on the adjacent branch. Okay, got it?
[Note: The terminology is actually much more complex than I imagined. One line in the 55-page Spearman and Hardy (1985) chapter entitled "Integument" reads, "There are seven basic types of feather: contour feather, semiplume, down feather, powder down feather, hypopenna, filoplume and bristle." Seven basic types? Yipe! As far as I can tell, the interlocking mechanism is only found on contour feathers, i.e. those covering the body, wings, and tail.]
To get a look at the diagram in Miller and Harley, check out the newsgroup alt.binaries.pictures.misc, picture "feather1.gif". I scanned it in from the book. Most of the barbules have more than one hamulus, a forked one at the tip of the barbule and several more down the length of the barbule. An actual electron micrograph of a murre feather is shown in "feather2.gif" (from Spearman and Hardy 1985). Pay special attention to the barb on the right- see how its barbules/hamuli have a fairly large curve diameter? The caption of this picture (you can read part of it) says, "Fig. 1.26. Scanning electron micrograph of a contour feather of a Common Murre (Uria aalge) showing the hooked distal barbules interlocking with the grooved proximal barbules. x2000. Reproduced by courtesy of Dr. J. V. Beer." A better view of the interlocking mechanism is shown in "feather3.gif", the caption of which reads, "Fig. 1.24. Portions of two barbs from the pennaceous part of the vane of a chicken remix showing the interlocking of proximal and distal barbules. From Lucas and Stettenheim (1972)." [I don't know what remix means -- maybe the preparation?] This one is also from Spearman and Hardy. Note that the grooved proximal barbules are quite deeply grooved. If anyone has trouble getting these images, email me and I'll send them to you direct! I'll leave them on my account for 3 weeks.
Now, this background information should convince everyone that there is an interlocking mechanism, hooks on one part and grooves on another. However, I submit that having two interlocking parts in no way damages evolutionary theory, and in fact gives evidence to strengthen it.
Paul Keck's recounting of How the interlocking mechanism on feathers probably developed:
In past times, feathers were probably first used as insulation, much like hair in mammals, and were probably hair-shaped, as some of those other types of feathers mentioned above still are. At some point, some of the proto-birds developed branching projections from the early feathers. These were better at insulating, and so natural selection favored those animals that possessed them.
The next step was probably selection for barbules which curled at the ends, hooking the barbules into the adjacent ones and thus making a better wind-shedding surface, like a windbreaker. (The underfeathers would make better insulators by staying fluffy and unhooked, so the downy type of feather would be retained.) At this point the barbules were probably still pretty much round in cross-section, with no grooves. Since the limited interlocking mechanism was an improvement over non-interlocked feathers, there would be a competitive advantage to having the hooks.
So, now we have hamuli hooked around barbule "petioles". Now go back to one of Darwin's assumptions that I've been pretty much taking for granted so far- variation. Some of these proto-birds had "petioles" slightly oval, or squarish, or crescent-shaped, as opposed to round. Please stress the "slightly" there! Now, one of these shapes was better than the others at holding the interlocking mechanism together (another idea of Darwin's). So, that proto-bird's offspring would survive better than offspring of the others, and so eventually replace them.
Fast forward a couple of hundred million years of the same variation, mutation, and selection, and you end up with modern bird feathers. Simple, no? Just time-consuming. The groove and hook did not evolve separately, as has been contended, but one in response to the other. The hooks were not useless without the grooves, they just work better with the grooves. You find this same pattern all through the living world. Eyes are another example.
I'll now say a few unresearched things about eyes. A common creationist claim about eyes follows the Feather Attack Mode (tm): "All those parts are useless without the others! See? They were created simultaneously!" Again, nothing could be further from the truth. Ask a Chlamydomonas algal cell, or a Euglena. They won't answer, but you can observe a very primitive eyespot on these cells. All it does is sense light. These algae have flagellae, so they can swim toward light if they get swept under a rock or water lily, e.g. This eye is intracellular, and basically spherical. A planarian (flatworm) has a cup-shaped depression lined with pigmented cells. This is equivalent to our retina. A nautilus is much the same, with its eye being likened to a pinhole camera (no lens or cornea, but almost spherical). Squids have an eye that adds a cornea and a spherical, rigid lens, much like fishes, and extrinsic eye muscles. Mammals have a soft, pliable lens for focusing. Birds have this and also double foveae, giving birds TWO "centers of concentration", i.e., they can "look right at" two things at once! So, these things don't need to be created all at once, and the "incomplete" eyes of lesser animals (i.e. not birds or squid) work fine. They allow creationists to read their Bibles, even though a bird could read and keep an eye on the kids at the same time.
So, you folks who think things that work well together had to be created together, I say: Nope! Try some other argument against evolution.
[Send for the pictures if you don't find them! I don't want anyone to have an excuse!]
Spearman, R.I.C and J.A. Hardy. 1985. Integument. In: Form and function in birds. Vol. 3. (A.S. King and J. McClelland, eds.) Academic Press, London. [part of at least a 4-volume set, written by veterinarians and anatomists]
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