What follows is a line-by-line analysis of the scientific accuracy of
the disclaimer. The text of the disclaimer is set in boldface type,
and my commentary is in plain type.
Message from the Oklahoma State Textbook Committee:
This textbook discusses evolution, a controversial theory, which some
scientists present as scientific explanation for the origin of living
things, such as plants and humans.
This statement is a deliberate attempt to mislead young readers
about the scientific standing of evolutionary biology. Within the scientific
community, evolution is anything but controversial. Rather, as the National
Academy of Sciences states, evolution is "the most important concept
in modern biology" (NAS 1998, viii). Saying that "some" scientists present
evolution as the explanation for the origin of species is equally misleading.
It is like saying that "some" scientists believe that matter is composed
of small units they call atoms. That statement would also be true, but
would convey a false sense of uncertainty regarding atomic theory. A
more accurate statement would tell students that evolution is accepted
by the vast majority of life scientists around the world, and by every
leading scientific organization in the United States including the National
Academy of Sciences, as the best available explanation for the origin
of species.
No one was present when life first appeared on earth.
Absolutely correct.
Therefore, any statement about life's origins should be considered
as theory, not fact.
This statement manifests a serious misunderstanding of the scientific
usage of the terms "theory" and "fact". A theory in science is an explanation
of a natural phenomenon, and a fact is a confirmed observation. An example
of a fact would be that there is great consistency in the sequence of
fossils in the fossil record, with no major branch of the tree of life
being out of order (for example, fossils of mammals are never found
in the Devonian Period - a time marked by the diversification of bony
fishes and the appearance of the first amphibians and insects). Another
fact is that living species tend to be found where their fossil ancestors
are also found. We make sense of these and many other confirmed observations,
or facts, with the explanation that living things share common ancestors,
from which they have diverged. This explanation is the theory of evolution,
an extremely strong and well-supported theory. The disclaimer will confuse
students about these important elements of science. Theories explain
facts, and contrary to the impression given by the disclaimer, this
means that theories are more important than facts.
The disclaimer also will confuse students about the nature of science
by implying that science concerns only directly observable phenomena.
Actually, many scientific discoveries are made about phenomena that
are not directly observable, such as those that are too far away (astronomy)
or too small (particle physics) as well as those that occurred in the
past (geology and evolutionary biology). That "no one was there to see
it" does not mean that it cannot be studied scientifically or that we
cannot have confidence in our explanations.
Ironically, well-written science textbooks place even less confidence
in current ideas about how life may have originated than the disclaimer
does. Typically, ideas about the origin of life are regarded as hypotheses,
placing them a rung lower on the scientific hierarchy of ideas than
the textbook committee was willing to do. (A typical example is this:
"How then did life begin? ... Although several hypotheses have
tried to explain how life may have arisen, we may never know the answers"
[Miller and Levine 1998, 398].) The disclaimer makes a serious error
by elevating current hypotheses about the origin of life to the status
of theories (which would mean that they are generally accepted by the
scientific community).
The word evolution may refer to many types of change. Evolution describes
changes that occur within a species. (White moths, for example, may
evolve into gray moths). This process is micro evolution, which can
be observed and described as fact.
Evolutionary biologists use "microevolution" to refer to the processes
(most of them having to do with genetics) that produce evolutionary
changes in populations of species: natural selection, mutation, migration,
genetic drift, and other mechanisms. The writers of the disclaimer apparently
share this definition, and are correct in noting that we can observe
these processes at work.
Evolution may also refer to the change of one living thing into another,
such as reptiles into birds. This process, called macro evolution, has
never been observed and should be considered a theory. Here the
writers of the disclaimer do not use the scientific meaning of the crucial
term. "Macroevolution", for evolutionary biologists, refers to a range
of processes having to do with the pattern of evolutionary change: how
groups are related to one another above the level of the species, rates
of evolutionary change, the behavior of lineages over time, and so forth.
But in the disclaimer, the term "macroevolution" means merely the general
principle of evolution: that living things have descended with modification
from common ancestors. This is not what macroevolution means in science,
and to use the term as a synonym for evolution misleads and confuses
students.
Clearly, the writers of the disclaimer want students to reject the idea
that living things have a common ancestry, and they are in the bind
of having to accept well-understood and widely-demonstrated processes
of evolutionary change, which, over time, would result in evolution.
The reason for this is at bottom a sectarian religious belief known
as "special creation": that all living things were created in their
present form and did not descend with modification from common ancestors.
Special creation is not supported by science - regardless of how the
authors of the disclaimer attempt to redefine scientific terms.
Evolution is not rigidly divided into two types of change -microevolution
and macroevolution - as the disclaimer implies. Macroevolution, for
example, may be used to refer to the process of speciation, to major
evolutionary transformations, or both. Most importantly, it is commonly
accepted among evolutionary biologists that microevolutionary changes
(whether caused by natural selection or by genetic drift) can accumulate
so as to cause reproductive isolation, hence leading to speciation or
macroevolution. Has macroevolution "never been observed"? A recent study
(Reznick and others 1997) evaluated the observed rates of evolutionary
change in populations of guppies (Poecilia reticulata) in the
wild. The rates of evolutionary change observed were "up to 7 orders
of magnitude greater than rates inferred from the paleontological record."
In other words, field studies of natural selection show rates of change
easily more than large enough to account for the macroevolutionary changes
documented in the fossil record. This is just one of many studies that
cast serious doubt on the assertion that macroevolution has "never been
observed." (The researchers also note: "Our work cannot address the
efficacy of mechanisms other than natural selection, but it extends
our understanding of what is attainable through this process. It is
part of a growing body of evidence that the rate and patterns of change
attainable through natural selection are sufficient to account for the
patterns observed in the fossil record" (Reznick and others 1997: 1936).
Evolution also refers to the unproven belief that random, undirected
forces produced a world of living things.
This statement is false on 2 counts. Evolution is not a "random" process,
and to characterize it so seriously misleads students. Natural selection,
the most important force driving evolutionary change, is not random
at all, but an observable, verifiable process that fine-tunes variation
in populations of a species to the demands of the environment in which
they live. It is true, of course, that variation in a species arises
from sources such as mutation and sexual recombination, which are inherently
unpredictable. Therefore evolution, like any historical process, can
be influenced by random forces.
But a larger problem with this statement is the attribution to evolution
of an idea outside of science. Whether evolution is "undirected" or
"directed" is a matter for theology or philosophy, not of science. Writers
of the disclaimer wish for students, most of whom are religious, to
believe that acceptance of evolution is incompatible with faith. This
is demonstrably false: far too many scientists (and clergy) accept both
evolution and a God who creates through evolution. Students should not
be taught that evolution equates with atheism, yet, incredibly, that
is exactly what this portion of the disclaimer says.
There are many unanswered questions about the origin of life, which
are not mentioned in your textbook, ...
It is absolutely true that there are "many unanswered questions about
the origin of life", and most biology textbooks point this out in far
greater (and more accurate) detail than does the disclaimer. Indeed,
there are unanswered questions in each and every area of biology, making
biology an exciting and vigorous discipline. The disclaimer, however,
does not seek to draw student attention to unanswered questions in biochemistry,
ecology, or physiology; it singles out evolution for special attention,
as if it had special difficulties that other fields do not.
Scientifically, this is not correct, and the next few sentences of the
disclaimer show just how badly informed its authors were:
... including: Why did the major groups of animals suddenly appear
in the fossil record, known as the Cambrian Explosion?
This question seriously misleads students about the actual natural history
of this planet. The term "major group" lacks scientific meaning. Many
students, for example, might regard the mammals as a major group. Mammals,
however, did not appear during the Cambrian explosion, but rather in
the Triassic, nearly 300 million years later. The same can be said of
birds, insects, reptiles, and amphibians, each of which are major groups
in the ordinary meaning of the term, and none of which appeared in the
Cambrian period. Clearly, the authors of the statement could have prevented
such confusion by referring only to the animal phyla instead
of "major groups".
Unfortunately, even if they had done so, the question would still be
misleading. Not all animal phyla originated during the Cambrian. Compounding
this serious mistake, the authors of the disclaimer seem to be unaware
that the first multicellular animals appeared on earth during the Ediacaran
Period, and many predate the Cambrian by more than 100 million years.
Why have no new major groups of living things appeared in the fossil
record in a long time?
This peculiar question requires students to determine what is meant
by a "major group" and also what is meant by "a long time". Neither
term, of course, has any scientific meaning. One might regard 100 years
as a long time, and it is indeed true that no new phyla have originated
in the last 100 years. However, by standards of geologic time, one of
the most important "major groups of living things" did indeed originate
recently. Flowering plants (the Anthophyta) appeared for the first time
in the Cretaceous, roughly 125 million years ago. Flowering plants appeared
only in the last 3% of the 4.5 billion years of the planet's geologic
history, which certainly qualifies as recent. Therefore, this question,
which overlooks the recent evolutionary appearance of flowering plants,
makes blatantly wrong presuppositions.
Why do major groups of plants and animals have no transitional forms
in the fossil record?
This question also makes blatantly wrong presuppositions. The fossil
record is, in fact, replete with splendid examples of transitional forms,
as the National Academy of Sciences has taken pains to point out:
So many intermediate forms have been discovered between fish and amphibians,
between amphibians and reptiles, between reptiles and mammals, and along
the primate lines of descent that it often is difficult to identify
categorically when the transition occurs from one to another particular
species. Actually, nearly all fossils can be regarded as intermediates
in some sense; they are life forms that come between the forms that
preceded them and those that followed (NAS 1999: 21).
How did you and all living things come to possess such a complete
and complex set of instructions for building a living body?
This is an excellent question, and students would be well-advised to
keep it in mind as they study biology. They may wonder why, for example,
the "complex set of instructions" referred to by this sentence includes
the genetic remnants of an ancient infection by an HIV-like virus. The
interesting fact about these genetic remnants is that they are found
not only in humans, but in our closest primate relatives, indicating
that these viral DNA sequences entered the genome roughly 30 million
years ago. As the investigators who made this discovery pointed out,
the existence of identical sequences in closely related species is "very
good evidence" that we share a common ancestry with these other primates
(Yang and others 1999). As the National Academy of Sciences has written,
"compelling lines of evidence demonstrate beyond any reasonable doubt
that evolution occurred as a historical process and continues today"
(NAS 1998, 16).
Study hard and keep an open mind. Someday you may contribute to the
theories of how living things appeared on earth.
At last, some excellent advice!
By any standard, this disclaimer fails even an undemanding test of scientific
literacy. Twelve statements are included in the disclaimer. Of these,
only 5 are free of major errors. Three are seriously misleading, and
4 are downright false. A biology teacher grading this disclaimer based
on the proportion of correct answers would calculate a score of no more
than 42% - a failing grade.
Our students deserve better.
To be sure, the disclaimer's admonition that students study hard and
keep an open mind fits the best traditions of scientific study. But
keeping an open mind does not mean that students should intentionally
be taught nonsense, nor does it mean that we should pretend to know
less than we do about the natural history of this planet and the origins
of species, including our own. Healthy skepticism is at the core of
a scientific education, but elevating falsehoods and half-truths to
the status of scientific theory most definitely is not.
I would argue that any textbook, indeed, any course in the biological
sciences should tell students the plain and simple truth, as described
in a single sentence by the National Academy of Sciences: that "[b]iological
evolution is the best scientific explanation we have for the enormous
range of observations about the living world" (NAS 1999: 28).
Author's Address
Kenneth R Miller
Department of Biology
Brown University
Providence RI 02912
References
Miller KR, Levine J. Biology: The Living Science. Upper
Saddle River (NJ): Prentice-Hall 1998.
National Academy of Sciences (NAS). Teaching about Evolution and
the Nature of Science. Washington DC: National Academy Press 1998.
February 7, 2001
