Reports of the National Center for Science Education

Dissecting the Disclaimer

Recently the state of Oklahoma almost adopted a disclaimer to be placed in science textbooks that mention evolution and are used by public schools in the state. (See RNCSE 1999; 19 [5]: 7-8, 1999; 19 [6]: 11-2, and 2000; 20 [1-2]: 21). RNCSE readers will recognize that the wording of the Oklahoma disclaimer is taken directly from the infamous original textbook disclaimer proposed for textbooks in Alabama (see NCSE Reports 1995; 15 [4]:10-1). Unfortunately, the disclaimer is laden with scientific inaccuracies and distortions that will confuse students about the nature of science and the science of evolution. Such statements place an unwelcome burden on teachers, who must correct this misinformation for their students. They also introduce the dangerous precedent of setting official statements by public officials at odds with scientific accuracy and good educational practice.

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).

By Kenneth Miller
This version might differ slightly from the print publication.