by Leslie K. Johnson
1994

This paper is a response to a presented paper.

Original author's comments on this response.


Abstract: Dr. Behe argues that a protein performing a given function in
the complex environment of the cell is such an improbable thing that it
could not be expected to arise in the time span available on earth. The
problem with his formulation is this: the process he models is not the
same process described by the theory of evolution. Evolution requires
inheritance, mutation, and selection. Dr. Behe's process involves only
inheritance and mutation. Once you have a simple replicating structure
(inheritance) that from time to time suffers changes in its replication
code (mutation), and particular mutants arise that out-multiply others
(selection), then the mutant type becomes common, forming the background
population in which the next winning mutation occurs. In this way, each
stepwise "gain" (in light of the final result) is consolidated.

A PROTEIN HAS BEEN PRESENTED as a complex thing. It is. There are limited
ways it can be modified and still function in the cell. That is true. The
exact ways a particular protein can differ without destroying function
have been investigated experimentally with exquisite technique. A protein
is in essence a chain of discrete beads or elements of finite number and
of describable relative availability for stringing. Therefore all possible
ways of randomly constructing a chain of equivalent length can be simply
calculated. The elements in a protein chain are viewed as steps that have
to have occurred.

In such a model, with a chain of any appreciable length, and an amino acid
soup of any appreciable diversity, the probability of getting one of the
few possible chains that "work" quickly gets exceedingly small, so small,
that for our minds to grasp the unlikelihood, we must resort to metaphor.
All this is true.

The process Professor Behe describes-a process of stepwise amino acid
substitutions adding up to an improbable product; a process extended in
time but with a probability of occurrence analyzed no differently than had
it all been assembled in "one fell swoop"-is not analogous to the process
of evolution by natural selection. Yes, like organic evolution, there are
replication and mutation. But what has been left out are the filters, the
sieves that at every generation sift the outcomes. The sieve is natural
selection. No discerning selector is implied.

Selection is a way of describing the fact that, in the environment in
question, some of the variants will be more successful than others in
populating the next generation with their sort. These variants are better
at lasting long enough to make copies, and better at making relatively
many of these copies. No selector is implied, but "sense" does build
itself into the process. Which variants do relatively well is not entirely
haphazard. On average, successful variants surmount the complex challenges
of their environment by happening to be a bit more complex themselves in
the effective sorts of ways.

As this mechanical process is iterated, and variants of differing success
continue to pop up, the diversity in the total collection rises. Rising
diversity means that the environment in which the variants exist and
replicate gets more complex over time. So, yet more complex ways of
existing and replicating are the ones that work relatively better in later
generations. Viewed overall, the unfolding scenario has the look of
progress.

The analogy between typing monkeys and evolution has a flaw, which is
teleology. Teleology is a goal toward which something is working, In the
monkey example, the goal is the character string that spells "Drop the
anchor in one hour." The monkey types character strings of lengths similar
to the goal. Every time the random product gets the same letter in the
same place as the goal, that character is inserted in that site with each
succeeding string of letters the monkey types. Naturally, by and by, the
goal is reached. The teleology is not in the mind of the monkey, it is
true, but is present because the game is rigged.

A little less teleological is the transmogriftcation of everyday food
preparation into a practical, delicious showpiece of regional cuisine.
Night after night throughout the region, meals are prepared. Haphazard
elements affect the product: what's in season, what's on hand, what's
convenient at the time. Children poke at it, husbands mumble over it, but
once in a while someone says, "Hey, that's delicious-write it down!" A
recipe appears. The recipe gets replicated whenever a guest or a relative
asks to have it, and it is replicated even more when it is included in the
PTA fundraiser cookbook. Each new owner of the recipe is likely to alter
it a bit, leaving out a disliked ingredient, adding a radish rosette. New
environments affect what is made: microwave ovens, say, or the Surgeon
General's recommendations. A recipe that is really successful in leaving
descendants bears a name everyone recognizes- fajitas, ginger beer,
bubble-and-squeak.

So, with somewhat accidental variation, "filters" that operate every time
the dish is made, and replication, we have an outcome: a regional dish
that could not have been specified at the outset in the cabins of the
first local settlers. The analogy, however is flawed. Design does creep
in. Food preparers do think, and have short-term goals in mind.
Other analogies avoid the problem of teleology. You and I are the highly
improbable outcomes of all the chance meetings, feelings of love, mutual
attractions, rapine roughness, release of particular ova, and plain old
fluid dynamics of all the couplings of all our ancestors since the dawn of
history. We were not envisioned in our glorious uniqueness by any of the
players in our past. But this analogy, too, is imperfect. We are,
arguably, no more complex than our ancestors in Mesopotamia, or wherever.
It is Tom Ray's computer program that makes the best analogy I know of to
the process of organic evolution. The elements of replication, production
of new variation, and non-teleological. automatic selection are present.
These elements produce novelty, complexity, diversity.

The best example, of course, is the real thing: organisms surviving and
reproducing in environments in which some types do better than others.
Successful variants tend to be those good at acquiring whatever the needed
resources are, converting them efficiently into growth and offspring,
lasting long enough to do so, and helping organisms with genotypes most
like one's own. For those wanting to understand what evolutionary
biologists mean by evolution, organismal biology merits careful study.
To touch on something else, the production of new variants is sometimes
equated with point mutation. A point mutation is an altered nucleotide in
the genetic material. An analogy to this is a substitution in a typed
character string. When evolutionary biologists speak of mutation, they
mean point mutation and more. Mutations are Spontaneous gene changes,
including point mutations at one or several nucleotides, changes in
chromosome number or structure, and shuffling of parts of genes, as, for
example, transposition of gene segments.

All this becomes significant when we seek to understand evolutionary
attainment in groups as different as bacteria, fungi, green plants, and
mammals. Biochemically, it looks as if all life started from one basic
kind a long time ago. During diversification, rather different modes of
organization were achieved, such as unicellularity, cellular
differentiation, or development that proceeds by induction. These modes of
organization put constraints on what further kinds of innovation were
likely to occur.

Evolution in bacteria, for example, tends to involve minor changes in the
code, RNA, which in turn affects metabolic pathways. Flowering plants are
developmentally simple and morphologically plastic, and often speciate by
multiplication of chromosome number. They are essentially constrained from
evolving nervous systems by the cellulose walls that enclose each cell.
Mammals have complex, interactive development. Their evolution frequently
involves regulatory genes that affect developmental timing and
differential sensitivity of different parts of the neuroendocrine system.
A small difference early leads to a big difference in adult structure and
function.

This means that evolution can be expected to occur with differing tempo
and mode at different times during the history of life and in different
taxonomic groups. As we learn more and more about molecular genetics and
developmental biology, we can make more and more refined predictions about
which groups are likely to speciate a lot and under what circumstances,
and what sorts of novelty will appear in the daughter species. Deepened
understanding will permit new tests of the validity of the theory.
Darwinism has met the challenge of the explosion of new information
generated by the growth of molecular biology, and is becoming integrated
with it in ways that get richer with the passage of each publishing day.
The theory is healthy.

True, one can find practicing scientists who are skeptical about
evolution. Without having conducted a survey, I will brazenly hypothesize
that such skeptics will be drawn disproportionately from technology fields
and fields that focus on more physicochemical levels of organization.
These fields have principles of organization of their own which need not
be much perturbed by the parade of life. Such principles include quantum
mechanics or electron orbital theory.

The big theory for biologists, however, especially those who work at the
most emergent levels of organization (such as social behavior), is
evolution by natural selection. As an organizing principle that is
bolstered by, tested against, and modified according to evidence, it has
tremendous explanatory power.

Take one small set of biologists, those who work on amphibians, a minor
group of animals. Since 1970, amphibian biologists have been producing
more than 1,000 titles per year, according to the Zoological Record.
Topics include vocalization, larval traits, endocrinology, the fossil
record, reproductive strategies, development, the musculoskeletal system,
sensory reception, molecular evolution, cytogenetics, biogeography, and
digestion. William Duellman and Linda Trueb produced a big new book, The
Biology of Amphibians. The framework into which they fit all this stuff is
evolution. This would be true as well if they made an Encyclopedia of
Amphibians.

With evolution as an organizing scheme, such an encyclopedia would be
compelling and understandable. Without evolution, it would be as exciting
as a fourteen-volume set of urban telephone books.

This is why evolution works for me and for my fellow biologists.

Foundation for Thought and Ethics.

Copies of the book Darwinism: Science or Philosophy are available from:
Foundation for Thought and Ethics