Author: Paul Keck (keck@athena.cs.uga.edu) Title: Feathers: Created or Evolved? Date: Nov.

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Author: Paul Keck (keck@athena.cs.uga.edu)
 Title: Feathers: Created or Evolved?
  Date: Nov. 25, 1992
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Bob 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 (refs 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
[sic, ??] 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, [C'ists- attack here! :-)]
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 cresent-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 seperately, 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 C'ist 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 sperical).
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 C'ists 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.

Paul Keck  keck@athena.cs.uga.edu [Send for the pictures if you don't find
them!  I don't want anyone to have an excuse!]

Literature Cited

Miller, S.A. and J.P. Harley. 1992. Zoology. Wm. C. Brown Pub., Dubuque, IA [a
general zoology text I had lying around the house.. free sample :)]

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 vetrinarians and anatomists]