Biologists’ Statement on Teaching Evolution (1967) *

The following statement on the evidence for biological evolution, intended for supporting its teaching in public schools, was framed in connection with a debate on the matter held in Little Rock, Arkansas, last summer. (For an account of the occasion leading to the debate see American Biology Teacher, 1967.) Technically, at any rate, such teaching is still illegal in Arkansas, Mississippi, and Tennessee. It is expected that a court in Arkansas will decide that this ban constitutes an infringement on academic freedom. However, so long as the conception of evolution is thought to be founded on faulty evidence, and even to be subversive, by much of the public; by many of their leaders in these states; and not a few others; the teachers in the public schools there will continue, for the most part, to be afraid to teach it. In fact, a considerable fraction—even of high school biology teachers—will, as they do now, fail to regard evolution as credible for themselves.

Despite the fact that many of these teachers today are using the Biological Sciences Curriculum Study texts, in which evolution is taken very seriously, many are still omitting or soft-pedalling the subject. It is for this reason that the present statement was framed by this writer, and that he was able to obtain for it the signatures of the vast majority of biologists to whom the statement was sent. It is not intended to represent the voice of authority but to show how convincing to earnest students of evolution has been the great amount of evidence, of very diverse kinds, regarding it—evidence that has been gathered objectively and subjected to very free criticism. 

Professor Emeritus
Zoölogy Department
Indiana University


It has for many years been well established scientifically that all known forms of life, including man, have come into being by a lengthy process of evolution. It is also known today that very primitive forms of life, ancestors of present-day microbes, arose thousands of millions of years ago. They constituted the truth of a “tree of life” which in growing branched more and more. That is, some of the later descendants of these earliest living things, passing beyond the level of microbes, became ever more diverse in their kinds, and increasingly different from one another, and some of them came to have a much more complicated organization that we call more advanced. Man and the other highly organized types of today constitute the present end-twigs of that tree. The human twig and those of the ages sprang from the same ape-like progenitor twig. 

Scientists consider that none of their principles, no matter how firmly established, and no ordinary “facts” of direct observation either, are absolute certainties. Some possibility of human error, even if very slight, always exists. Therefore, instead of there being sharp lines separating “hypothesis,” “theory,” and “fact,” there is a sliding scale of probabilities. Scientists welcome the challenge of further testing of any view whatever. They use such terms as “Firmly established” only for conclusions founded on rigorous evidence that have continued to withstand searching criticism. The principle of biological evolution, as above depicted, meets these criteria exceptionally well. It rests on a multitude of discoveries of very different kinds that concur and complement one another. It is therefore “accepted” into man’s general body of knowledge by scientists and by other reasonable persons who have familiarized themselves with the evidence.

Among these sources of these different kinds of evidence are the following: (1) Fossil records, now abundantly known, of previously existing life. (2) Careful comparisons of the structure of different living things that are visible to one’s naked eye by inspection and dissection of them. (3) Careful comparisons of their inner workings, that is, their physiology, including their behavior. (4) Comparisons of their development from the earliest embryos to the oldest adult types. (5) Comparison of their microscopic and ultra-microscopic structures and of these transformations they can be seen to undergo during the course of living. (6) Comparisons of the details of the complicate chemistry of different living things, an extremely deep and intricate subject nowadays. (7) Studies of the pattern of distribution of different kinds of living things on this earth, both at present and in the past. (8) Studies of how plants now cultivated and animals now domesticated have changed as a result of selection practiced on them by man, and the elaborate and farreaching laboratory and field studies in genetics that show how, in the course of generations, separated populations of living things become different from one another in their inherited constitutions.

It would be impossible in a few hours to make clear the significance and the weight of this great mass of extraordinary and intricate findings to persons not already possessed of a considerable biological background. In fact, even they [people who do possess such a background] could hardly grasp them in full without long and deep study, preferably extending over years. Moreover, in recent years the evidence in most of the lines mentioned has accumulated much further. This has resulted in the ever firmer establishment and improved understanding of biological evolution, including the further confirmation of the principle of natural selection that Darwin and Wallace, more than a century ago, showed to be an essential part of the process of biological evolution. There are no hypotheses, alternative to the principle of evolution with its “tree of life,” that any competent biology of today takes seriously. Moreover, the principle is so important for an understanding of the world we live in and of ourselves that the public in general, including students taking biology in high school, should be made aware of it, and of the fact that it is firmly established even as the rotundity of the earth is firmly established.


The following signatories are among the 177 persons who signed the statement:

George W. Beadle, President, University of Chicago;
James F. Crow, Chairman of the Department of Medical Genetics, University of Wisconsin;
Max Delbrück, Professor of Biology, California Institute of Technology;
Bentley Glass, Distinguished Professor of Biology and Academic Vice President, State University of New York at Stony Brook;
W. W. Howells, Professor of Anthropology, Harvard University;
Bill H. Hoyer, Head, Biochemistry and Biophysics Section, Virus Laboratory, Institute of Allergy and Infectious Diseases, National Institutes of Health;
William D. McElroy, Professor and Chairman of Biology, Director of McCollum-Pratt Institute, Johns Hopkins University;
H. Malcolm Owen, Head, Biology Department, University of the South, Sewanee, Tennessee;
Gregory Pincus, Research Director, Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts;
Colin S. Pittendrigh, Professor of Biology and Dean of the Graduate School, Princeton University;
Tracy M. Sonneborn, Distinguished Professor of Biology, Indiana University;
S. Spiegelman, Professor of Biology, University of Illinois.

[Reprinted with permission from Bulletin of the Atomic Scientists 1967; 23(2): 39–40.]

Table of Contents