The Illogic of Creationism
                     An Essay Review
             by Michael T. Ghiselin, based on
              "Evolution: A Theory In Crisis"
                    by Michael Denton
          Adler & Adler, Bethesda, MD 1986,$19.95

William Harvey's book entitled "De Motu Cordis et Sanguinis in
Animalibus" was published in 1628. It established beyond reasonable
doubt that the blood circulates, and it overthrew the ancient
physiology of Galen. So compelling were Harvey's arguments that his
conclusions became the consensus among the learned community within
his own lifetime, even though the passage of the blood through the
capillaries had yet to be seen.

Charles Darwin's book entitled "On The Origin of Species by Means of
Natural Selection" was published in 1859. It established beyond
reasonable doubt that organisms of different species are united by
common descent, and overthrew the traditional view that they had come
into being through supernatural acts. So compelling were Darwin's
arguments that the evolutionary conception of the living world became
the consensus among the learned community within ten years, even
though the sort of fossil record that would have been all the more
convincing was not yet available.

Harvey's idea that the heart is a pump and provides the main driving
force behind the circulation remains a fundamental principle in
cardiac physiology. So too with Darwin's principle of selection,
without which so much of biology would be utterly unintelligible.
Indeed, we owe much of our present understanding of the heart and
blood to the fact that anatomists and physiologists know that such
things evolve.

All this is common knowledge, or at least it ought to be. No properly
educated person would entrust his own life, or that of his child, to
a physician who did not know that the blood circulates and why it
does. If a medical practitioner claimed that the blood does not
circulate his intellectual credentials and professional integrity
would be questioned. So we would look very carefully at his claims,
admitting perhaps that all sorts of things are possible and we would
not pre-judge the issues. If we found that his premise were false and
his logic formally invalid, we would consider him discredited; and if
we found him marketing such notions to a gullible public we would
denounce him as a quack.

The same applies to scientific matters in general, including those
from which modern cardiac physiology derives its legitimacy. If
somebody said that the circulation of the blood is "just a theory,
not a fact," we would take it as an insult to our intelligence. That
the blood circulates is a fact, in the sense that the blood does in
truth circulate. The theory presented in Harvey's book makes the
structure of the blood intelligible in the light of the fact that
the blood circulates. By the same token there is no contradiction
in speaking of evolutionary theory on the one hand, and the fact that
evolution has occurred on the other. One does not have to be a
professional logician, or to know the technical term for it in formal
logic to recognize such a flagrant instance of the fallacy of false
disjunction. But the general public, having little acquaintance with
theories anyway, is apt to be misled if such matters are not clearly
explained in terms they can understand. And fallacious reasoning can
be subtle. Logical fallacy becomes all the more pernicious when
coupled with false premises of the sort that only an expert can
identify as such.

A book by an author who is obviously incompetent, dishonest, or
both -- and it may be very hard to decide which is the case -- 
ordinarily is not worth the attention of a professional scholar.
If, however, the deficiencies are not apt to be recognized by the
audience to whom a work is addressed, warning potential readers
might be a valuable service. And discussing some examples of
fallacious and false premises can sometimes be a useful exercise.

Michael Denton attempts to convince his readers
that something is wrong with evolutionary biology. This he
does primarily by attempting to resurrect one of the
positions that revolutionary biology rendered untenable
in the first place, namely the typological interpretation
of biological classification systems (or taxonomy). A
typologist would have us believe that organisms exist
in nature as members of discrete classes, in the sense
that everything clearly falls under one head or another.
Hence each and every group can be rigidly defined, and
there can be no overlap or intermediates between them.
If this be so, then it would appear that either the groups
in question have not evolved, or that if they have evolved,
they have done so by large and discontinuous steps -- by
"saltation." Because the current version of evolutionary
theory rejects genuine saltations, there would seem to be
something problematic about it.

Contemporary philosophy of taxonomy has a ready
answer to Denton's argument. The groups, or taxa as they
are called, are not classes in Denton's sense at all. They
are lineages, or branches of genealogical trees. Therefore
we should not expect to "define" them at all, in the sense
that an organism simply must have a given property to occupy
some position on a tree. The mischief comes from efforts to
translate the branching diagram into a heirarchical
arrangements of groups within groups.

Denton claims that organisms always possess the
diagnostic features that purportedly "define" each group.
If he understands why this is so, he does not tell his readers.
Of course, if you go out in the wild, and find an animal
with hair, you can be reasonably sure that it is a mammal --
though perhaps you might have trouble, say, with the "hair"
on a tarantula. Why should this be? For the simple reason
that whenever taxonomists find a group, they go through a
great deal of material, looking for characters that happen
to be present in all specimens of the group. These they
treat as diagnostic -- which means that they are useful
in identification, like the symptoms in a doctor's diagnosis
of an illness. If they later find a specimen that belongs
to the group, but does not have the diagnostic feature,
they decide that the feature is not diagnostic after all,
and perhaps look for other ones. The whole argument is
circular, as Darwin clearly explained in 1859.

By the same token, Denton tells us that as a rule
taxonomic groups are separated from one another by gaps,
with few intermediates between them. Of course. One
traditional practice among taxonomists has been to delimit
groups at precisely those places where the gaps , for
whatever reason, occur. They sometimes get filled in, as
when expeditions are sent to previously unexplored areas,
and the gaps get de-emphasized in the new systems of
classification.

Denton alleges that few if any intermediates have
been found between taxonomic groups. But he gerrymanders
the evidence so as to rule out the kind of intermediate
that most of us would consider a decent example. Consider
the following diagram, which represents a genealogy among
objects denoted by letters:

     E     D    C
     \     \   /
      \     \ /
       \     B
        \   /
         \ /
          A
          |
          |

According to one not unreasonable usage, the
lineage BD is "intermediate" between AE and C. So D in a
sense would fall between E and C. (Invertebrate chordates
such as sea-squirts and Amphioxus, which have notochords
but not vertebrae, would thus be intermediate between
vertebrates and other invertebrates.)  Of course, E, D,
and C do not represent a direct, ancestor-descendant
relationship. A, B, and C do, and this is the only sense
of an intermediate that Denton will accept. When dealing
with extant creatures, we would only expect a certain
amount of change to have occurred between, say, B and D.
Furthermore, if we found a fossil specimen of B, we might
have trouble deciding whether it really was a specimen of
B, in the sense of occupying the exact point of bifurcation,
or whether it was located along AB or BC, or perhaps some
minor branch not shown on the diagram. Furthermore, if we
look at a fossil such as B, we find that it has some
properties present in C and D, but not in A -- Archaepteryx,
as close an intermediate as one could wish between birds
and dinosaurs, is a good example. But all this is precisely
what we would expect, given the fact that the objects are
united by descent with modification.

So these arguments turn out to be flagrant instances
of the fallacy of irrelevant conclusion: they do not bear
upon the question of whether we have been able to document
intermediate conditions such as must have existed if
evolution has in fact occurred. We have. The question that
was asked in the first place gets begged as well. Darwin
suggested that the fossil record was far less complete
than people thought. If so, then further research should
lead to an increasing number of items lying close to A or
B, and it has. Therefore the argument from lack of
intermediates can be turned on its head, and made to show
that evolution has in fact occurred, merely by adducing a
few of them.

To refute the proposition that no intermediates
occur, we need only show that *one* does occur: it is a
formally valid test for universal negative proposition.
(To refute "All men are immortal" it suffices to kill just
one of them.) In the above example, B would suffice. But
Denton accepts the creationists' version of logic, and
insists that we fight not just B, but A, and every other
object in the universe analogous to it. In other words,
he insists that we verify a universal affirmative. What
this means is clear if we let the letters in our diagram
stand for languages. Let B stand for Latin, C for French,
D for Portuguese, E for Russian. In B, we we do have a well
documented common ancestor. But what about A? Unless I am
mistaken, we have no documents of the common ancestor of
the Slavic and Romance languages. And even if we did, the
creationists would simply ask for the common ancestor of
Nahuatl and Basque.

Such is the logic, if we may dignify fallacious
reasoning with such an epithet, upon which "creation science"
rests. That logic is inseparable from its content, for the
movement has presented us with one long series of excuses
for evading the canons of scientific evidence, in order to
suppress truths that some people find objectionable. Insofar
as special creation has been treated as a scientific hypothesis,
it was decisively refuted in 1859. The only way to get around
that fact is to repudiate not just some particular findings
of science, but its very foundations in logic itself. But if
logic -- and that means everything from higher mathematics
to common sense -- has to be repudiated, then rational
judgment of every kind loses its validity. That is precisely
what the creationists want. If they can degrade your child's
intellect enough, perhaps he will become one of them.

Denton's book may be read as an able piece of propaganda.
As such it has many fine qualities. The rhetoric is by no means
as bad as the logic. Except in a few places the author maintains
a reasonable and earnest tone. The liberal use of end-notes
suggests that a considerable amount of work has been done,
and the reader unaware of what should have been cited but was
not may have some difficulty distinguishing the reality of
scholarship from mere appearances. The occasional use of
creationist cliches tips off only the more perceptive reader
to what motivates the author. The creationists need a book
that is not overtly creationist at all, but purports to be
motivated by purely scientific interests. So I do recommend
the book, but only as an example of how reason is getting
abused these days.