Bernard Shaw's Remarkable Religion: A Faith That Fits the Facts

204 Bernard Shaw’s Remarkable Religion
the number of such possible transformations is extremely limited (which,
incidentally, is why the spelling checker for a word processor can work).
Michael Behe uses the term “irreducible complexity” to describe systems
that are completely isolated in this fashion. His claim is that at the level of
biochemistry, the work of life is carried on by innumerable molecular
“machines” that are “irreducibly complex.” That is, they are composed of
several parts, all of which are necessary for proper functioning. Missing a
single part, the molecular “machine” would be useless not only for its
known biological function but for any other imaginable function as well. It
is thus impossible to imagine how it could evolve in small incremental
steps.
When critics challenge the randomness of Darwinism, they are not
claiming that Darwinism is an entirely random process (as they are accused
of doing); they are questioning whether, given the rarity of viable
changes that can be made in a complex system, such variations could arise
by chance within the necessary time. They also question whether gradual
changes could ever account for the systematic changes evolution seems to
demand.
To understand such systematic changes, one can take an example from
the world of machines. Since humans design and build machines, we understand
them better than organisms, so it is easy to imagine what would
happen if aircraft, for example, “evolved” through gradual changes. It is
not difficult to picture how the shape of the wing or of the fuselage might
gradually change. But how could it gradually move from a piston-driven
propeller engine to a jet engine? Any imaginable small steps to get from
one to the other would not be functional. The system has to change as a
whole. Intermediate steps would not be, in Darwinian terms, fit to survive.
Denton provides numerous examples of analogous transformations necessary
in animal evolution. A particularly intriguing example is the difference
between the lungs of birds and those of other vertebrates. Our own
lungs are constructed of a system of branching tubes that terminate in tiny
air sacs called alveoli. Air is sucked into those sacs and then forced out
again, the same way that it came in. It is an inefficient process because it is
impossible to get all the old air out before the new air is brought in. The
lungs of birds are constructed on an entirely different plan. The air moves
in one direction only, so that it passes all the way through the lung before
it is expelled. The lungs of other vertebrates are operated with relative
simplicity. Like a bellows, we open them to bring air in and squeeze them
to push it out. Birds require a more complicated mechanism to keep the air