Dear Editor:

Tom Davis's reply to Granville Sewell effectively responds to many of
Sewell's dubious objections to evolution.   Without attempting to be
comprehensive, I would like to address several additional points.

1.  Any biologist can tell you how systems that appear to be
"irreducibly complex" (i.e., all parts of the system are required for
the system to function) could evolve:  through scaffolding.  As H.
Allen Orr wrote in his perceptive review of Behe's book:

	"An irreducibly complex system can be built gradually by adding
	parts that, while initially just advantageous, become --
	because of later changes -- essential. The logic is very
	simple. Some part (A) initially does some job (and not very
	well, perhaps). Another part (B) later gets added because it
	helps A.  This new part isn't essential, it merely improves
	things.  But later on, A (or something else) may change in such
	a way that B now becomes indispensable. This process continues
	as further parts get folded into the system.  And at the end of
	the day, many parts may all be required." [1]

This and other reviews of Behe's book can be found online [2].


2.  Sewell draws an analogy between biological systems, coded by DNA,
and computer programs.  He writes "to anyone who has had minimal
programming experience this idea [that a significantly better program can
be made by accumulating small improvements] is equally implausible."
Sewell seems to be entirely ignorant of the field of genetic
programming, where what he claims is implausible is routinely
done [3].

The analogy between computer programs and biological systems is useful,
as far as it goes.  But like all analogies, it is imperfect.  If we
draw conclusions from our analogy which conflict with very strong
evidence -- conclusions such as life could not have evolved over time
-- then we should suspect that it is the analogy, not the conclusion,
that is mistaken.

In particular, here are some features of biological systems that are
not shared by most computer programs written by humans in modern
computer languages:  their "program" codes for the assembly of physical
systems; much of their "program" is historical legacy that is currently
non-coding; small changes to the "program" often do not change the
product (because the genetic code is robust and redundant); and
finally, biological systems are self-reproducing and exist in an
environment where they must interact with millions of competing
systems.

Sewell also seems unaware of programs, such as Tom Ray's Tierra [4],
which simulate evolution through competing pieces of computer code.


3.   Sewell claims that the record of a computer program's development
by humans "would be similar to the fossil record".  But there is one
similarity that we do *not* find.  A human designing a computer program
is free to incorporate improvements from programs developed by other
humans in other parts of the world.  On the other hand, this is
precisely what we do *not* see in biological systems.  (Horizontal
transfer does occur, but not separated by space and time.) The genome
of humans does not include evolutionary improvements discovered by
flowering plants, for example.  If today's biological diversity is the
product of "intelligent design", it is entirely remarkable that this
designer chose to make life appear to be arranged in a branching
hierarchy consistent with common descent, without incorporating
improvements across different branches.  If life is designed,
why does it look so much as if it evolved?


Jeffrey Shallit
Department of Computer Science
University of Waterloo
Waterloo, Ontario  N2L 3G1
Canada
shallit@uwaterloo.ca


[1] H. Allen Orr, Darwin v. Intelligent Design (Again),
Boston Review 21 (6) (1996-7).   Also available at
http://www-polisci.mit.edu/bostonreview/BR21.6/orr.html .

[2] Behe's empty box, http://www.world-of-dawkins.com/box/behe.htm .

[3] Zbigniew Michalewicz, Genetic Algorithms + Data Structures =
Evolution Programs, Springer, 1994.

[4] Tom Ray's Tierra home page, http://www.hip.atr.co.jp/~ray/tierra/ .