Evolution of Bird Feather and Aerofoil

In Michael Denton's book "Evolution: A Theory in Crisis," he described
the bird feather and how it is used to dynamically construct a complex
aerofoil that enables flight. For reference, I have included below
excerpts of Denton's discussion of the feather and aerofoil.

My question to the TalkOrigins group is: What is the latest scientific
explanation for how the feather and aerofoil evolved? Have fossil
'proto-feather' intermediates been found? Have any credible
evolutionary pathways from reptile scales to feathers been
established? Has there been any resolution between the 'from the
trees down' or 'from the ground up" scenarios for the evolution of
flight?

Thanks in advance for any information on this topic.
ofg

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Excerpts from Michael Denton's book:, Chapter 9

Each feather consists of a central shaft carrying a series of barbs
which are positioned at right angles to the shaft to form the vane.
The barbs which make up the vane are held together by rows of
barbules. From the anterior barbules, hooks project downward and these
interlock with ridges on the posterior barbules. Altogether, in the
flight feather of a large bird, about a million barbules cooperate to
bind the barbs into an impervious vane.

The feather is a magnificent adaptation for flight. Flight feathers
are remarkably light and strong and anyone who has played with one
will know how easily a ruffled feather can be repaired merely by
drawing it between the fingers. In addition to its lightness and
strength the feather has also permitted the exploitation of a number
of sophisticated aerodynamic principles in the design of the bird's
wing.

One problem common to all aerofoils is turbulence, which reduces lift
and causes stalling. Turbulence can be greatly cut down by the
provision of slots in the aerofoil which let through part of the air
stream and tend to smooth down the flow. Aeroengineers have used this
principle by placing a small subsiduary aerofoil in front of the main
wing, creating the so-called Handley Page slot. The use of feathers in
the design of an aerofoil lends itself admirably to the provisions of
slots, and most birds' wings exploit this technique. The use of
feathers also provides the bird with an aerofoil of variable geometry
so that it has the ability to vary the shape and aerodynamic
properties of its wing at takeoff, landing, and for various different
sorts of flight - flapping, gliding, soaring. In many birds, the
positioning of the feathers is maintained by an intricate system of
tendons which allow the feathers to twist in such a way that when the
wing is raised they open like the vanes of a blind, greatly reducing
resistence, but close completely on the downstroke, thus greatly
improving the efficiency of flight. One need only watch the darting-
backwards-and-forwards flight of the humming bird to grasp something
of the excellent aerodynamic properties of the feathered aerofoil.

.......................

An aerofoil based on the feathered design has, therefore, to satisfy a
number of quite stringent criteria before it can function and create
lift. It is significant in this regard that every single flying bird,
from Archeopteryx on, has possessed a highly developed aerofoil
consisting of a complex arrangement of fully developed flight
feathers.

......................

It is not easy to see how an impervious reptiles scale could be
converted gradually into an impervious feather without passing through
a frayed scale intermediate which would be weak, easily deformed and
still quite permeable to air. It is true that basically a feather is
indeed a frayed scale - a mass of keratin filaments - but the
filaments are not a random tangle but are ordered in an amazingly
complex way to achieve the tightly intertwined structure of the
feather. Take away the exquisite coadaptation of the components, take
away the coadaptation of the hooks and barbules, take away the
precisely parallel arrangement of the barbs on the shaft and all that
is left is a soft pliable structure utterly unsuitable to form the
basis of a stiff impervious aerofoil. The stiff impervious property of
the feather which makes it so beautiful an adaptation for flight,
depends basically on such a highly involved and unique system of
coadapted components that it seems impossible that any transitional
feather-like structure could possess even to a slight degree the
crucial properties.

.

Relevant Pages

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