Analysis of "Biology Text Review" by POSH


A pril 27, 2000

Kenneth R. Miller
Professor of Biology

Brown University
Providence, Rhode Island 02912

This document is a response to a review of the textbook BIOLOGY by Miller & Levine (Prentice Hall, New York). The review was placed on the Internet (URL: by POSH (Parents for Objectivity in Science and History) and presented to the Board of Education in Lawrence, Kansas.


In their opening summary the POSH reviewers admitted that they had not read the entire book, which makes it difficult to understand how they could come to a fair-minded evaluation of Biology by Miller & Levine. Nonetheless, I was delighted to read that the reviewers' general appraisal of our textbook was very positive. They wrote:


Naturally, I am happy that POSH found our book to be of high quality. Unfortunately, POSH did not evaluate our book for its overall effectiveness, relevance, and accuracy. Rather, they read the book for one purpose, and apparently or one purpose only: to examine "All parts directly pertaining to, or addressing the concept of evolution...." They do not explain why they take a special interest in just this one area of biology, leaving it to the reader to determine whether they have chosen this area in order to examine our book from a particular religious or political agenda.

The POSH document identifies one "Primary Problem," which it characterizes as confusion in the use of the term evolution. It also identifies three "Secondary Problems," which are (A) Omission of information, (B) Study questions which lead to confusion, and (C) Problems of missing or false information. I have done my best in the pages that follow to respond, point-by-point, to the criticisms presented by POSH.


Primary Problem:
Confusion in the use of the term 'evolution'

According to the POSH statement, the evidence presented in our text that supports evolution is actually restricted to "microevolution," and not "macroevolution." They draw a clear distinction between these two terms:

All of the POSH criticisms in this section, which they regard as the "Primary Problem" with our book, revolve around the distinction between to "microevolution," and "macroevolution." POSH obviously believes that this is an important distinction, and that our textbook has misled students by not making the distinction clear; hence, the alleged "confusion" about the term and meaning of evolution.

RESPONSE: Evolution is not rigidly divided into two types of change, "microevolution" and "macroevolution," as POSH claims. 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 in such a manner that they ultimately cause reproductive isolation, and hence lead to speciation or "macroevolution."

Has macroevolution "not been observed?" A 1997 study by Reznick et al in the journal SCIENCE (Volume 275, 28 Mar 1997, pp. 1934 - 1937) evaluated the observed rates of evolutionary change in populations of guppies (Poecilia reticulata) in the wild. These researchers observed rates of evolutionary change "up to seven orders of magnitude greater than rates inferred from the paleontological record." In other words, field studies of natural selection show rates of change that are 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." (Reznick et al (1997) 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.")

As our textbook points out, evolution is best defined as what Darwin called "descent with modification," meaning that today's living species are the modified descendants of species that preceded them. As the most prestigious scientific body in the United States, The National Academy of Sciences, writes, evolution:

We agree with the National Academy, and we are proud that we have written a textbook that reflects the scientific viewpoint on this issue and articulates it clearly to students and teachers of biology.

The Galapagos Finches The scientific status of POSH's criticisms can be illustrated in a number of ways. Consider this statement:


As a look at our text will show, Figure 14-20 does not show finches at all, but rather several species of the Hawaiian honeycreeper. I can only assume that the POSH reviewers mis-identified the birds or failed to read the caption to the figure. The honeycreepers, of course, are excellent examples of adaptive radiation, and their evolution on the geologically-recent islands of the Hawaiian Islands is verywell-understood. However, what about the Galapagos finches (which are indeed giv en as an example of speciation on pages 306-307)? POSH's statement that the finches have "not become different life forms" says a great deal more about POSH than it does about evolution.

Darwin's finches are presented in our book as examples of the ways in which several modern species can be traced back in time to quite different ancestors. They are presented as evidence that the forces of natural selection can and do produce new species of organisms. Are these assertions supported by the scientific evidence? Yes. As the members of POSH should know, Peter and Rosemary Grant of Princeton University have gathered abundant evidence in the wild that natural selection can produce rapid morphological changes in present-day finch populations. Their work was popularized in Jonathan Weiner's Pulitzer Prize-winning book, The Beak of the Finch (Vintage Press, New York, 1994). Their studies show the efficacy of Darwinian mechanisms to drive the very mechanisms of evolutionary change that produce new species.

What about the assertion that the finches are descended from a common ancestor? This testable scientific claim has now been put to the test and is strongly supported by the evidence. Ecologist Kenneth Petren, collaborating with the Grants, has used molecular methods to test the hypothesis of common descent, and has found results that support the Darwinian account of finch evolution in every detail. Their work, reported in the February 22, 1999 issue of Proceedings of the Royal Society (B), also point to a specific mainland species as the ancestor of all the Galapagos finches.

Is it scientifically sound to minimize the importance of these findings, as POSH has done, by saying that the birds have "not become different life forms?" Not at all. The 14 distinct species found on the islands are well-recognized, distinct species that have emerged in less than 3 million years (the geologic age of the islands). The fact that well-studied Darwinian mechanisms can produce novel, distinct species in just a few million years contradicts their assertions that all observed evolution change is limited to variation within a species. Their proposal to classify this as an example of "microevolution," which they define as "relatively minor variations and adaptations," makes no scientific sense. The differences between species are not minor, and I suspect that POSH dismisses them as such in hopes that students will be encouraged not to recognize the scientific importance of well-documented examples of evolution such as the finches and the honeycreepers.


The Nature of the Fossil Record

POSH argues that our discussion of common ancestry is "dogmatic," because it suggests that all living forms are related by a process of common descent. This may well be true, they admit, but they argue that the fossil record does not support this interpretation:


There is "poor science" here, but it is not in our book. The POSH claim that the fossil record lacks "transitional species" is completely false. 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:


If the members of POSH wish students in Lawrence to be taught that the lack of "transitional species" is "patently clear," it should be clear that this recommendation is at odds with the facts of the fossil record and the consensus of the working scientific community.

A more specific allegation is given in POSH's assertions regarding the fossil record of snakes. Page 284 of BIOLOGY states that "Snakes, for example, evolved from four-legged ancestors." The members of POSH dispute this, and regard it is an example of "dogmatism."


Rather than dogmatism, this is an example of scientific accuracy. Key fossil finds in recent years have removed any doubt that the ancestors of snakes were four-legged animals, and if the members of POSH are sufficiently interested to consult the original literature, I would recommend they turn to a recent issue of the journal SCIENCE. There they will find an article entitled "A fossil snake with limbs" by Eitan Tchernov, Olivier Rieppel, Hussam Zaher, Michael J. Polcyn, and Louis L. Jacobs (Science 2000 March 17; 287: 2010-2012). Is it "dogmatic" to assert that snakes evolved from four-limbed animals when the fossils that document that ancestry are in hand? Certainly no scientist would find it reasonable to conceal such fossil finds from a summary of the scientific evidence in a textbook, but that is exactly what the POSH recommendations would do.

POSH also charges that page 309, Figure 14-21 "introduces dogmatically the concept that the bear, bird, dolphin, snake, alligator, and turtle evolved from the cotylosaur." This is not true. The caption to Figure 14-21 (fifth edition) reads: "Evidence from the fossil record indicates that modern day birds, mammals, and reptiles descended from reptilian ancestors." This statement, despite POSH's assertions to the contrary, is a factual summary of the scientific record on this point, as the National Academy of Sciences has made clear:


The "dogmatic" illustration that POSH objects to is, therefore, nothing more than a fair and reasonable summary of the existing scientific evidence.


Worksheet #1

This worksheet is clearly intended to document many of POSH's statements on the "Primary Problem" seen with Biology by Miller & Levine. As noted above, the sharp distinction drawn between "microevolution" and "macroevolution" is not accepted by the scientific community at large. The worksheet also contains a number of serious errors and misrepresentations of scientific fact. According to POSH, when studying the Galapagos finches students should learn that:


This statement is false. The "minor" variations they describe are nothing less than the characteristics that distinguish one species from another. The assertion that "no new information" can be gained by such processes is not correct. Molecular analyses of evolution show quite clearly that gene duplication, followed by natural selection can indeed produce "new" genetic information.


Of course variations have limits. The existing morphological and developmental patterns of a species always constrain evolutionary innovation, as biologists have realized for decades. However, POSH is careful not to say exactly what those limits are, except for the comic and facetious example of insects being unable to evolve "resistance" to a sledgehammer.


This is an extraordinary statement for a group that claims to be biologically-literate. POSH claims that the "minor variations" of microevolution are limited to change within the same "family." This would mean, incredibly, that the important differences between gorillas, chimpanzees, humans, and orangutans are nothing more than "minor" changes. Each of these species is, in fact, members of the same family (Hominidae). Biologists regard the species differences between humans and these great apes to be significant and important, but POSH apparently thinks otherwise.


It's true, of course, that finches already had beaks before undergoing their dramatic adaptive radiation into 14 distinct species on the Galapagos islands. However, the assertion that genetic information is "already present" in all observed and well-documented examples of evolution is false. Controlled laboratory experiments have shown time and time again that novel genes and biochemical capabilities can arise under the influence of natural selection.


The unsupported assertion that these two breeds of dog cannot interbreed has nothing to do with "missing" genetic information, and everything to do with the differences of size between these two dogs. It certainly has nothing to do with evolution, although it would be interesting to see if an in vitro fertilization procedure between these two dogs would produce viable offspring. POSH, however, asserts that "the genetic information is no longer present" without telling us what the "genetic information" is in these breeds that might be "missing."

The worksheet next tells students that "macroevolution" involves:


POSH's assertion that macroevolution involves events like "a snake becoming a bird" is almost comic in its misstatement of the process of evolution. Evolution does not involve one type of organism changing into another, existing type of organism, as this statement claims. Rather, evolution involves the splitting of a single species into two species with different characteristics. This has been repeated observed in the fossil record, and may have been observed under human observation as well (Steven Stanley, in his book Macroevolution, © 1998, Johns Hopkins University Press, Baltimore, MD, gives a number of examples, including five species of Hawaiian moth Hedylypta, which evolved in less than 1,000 years under human observation).


Worksheet #2

This worksheet asserts that there is considerable scientific doubt about the validity of evolutionary mechanisms. It tells students that "The process of forming and testing hypotheses, investigating and observing the smallest details of life forms, and publishing and discussing (even arguing about!) findings and theories is all part of the exciting world of science." I couldn't agree more!

The specific points in the worksheet then invite students to discuss the adequacy of evolutionary theory to account for the known facts of evolutionary change over time. These points include:


There is intense discussion over the relative importance of the factors that produce evolutionary change. Scientists do indeed debate the relative importance of natural selection, sexual selection, physiological selection, gene duplication, sexual recombination, and the other mechanisms known to drive evolutionary change. Therefore, this statement in the worksheet is valuable and constructive (it also does not criticize any portion of the text of Biology)

Unfortunately, many of the "questions" in the worksheet contain hidden, erroneous assumptions of their own.


The answer to the first question is yes. The implication of the second question is that "mutations" cannot provide the information needed for the development of new functions and organs. This is simply not true. Hayashi & Lewis (2000) "Molecular architecture and evolution of a modular spider silk protein gene" (Science 287: 1477-1479) is a perfect example of the ability of mutational mechanisms to produce new genes, new proteins, and new functional information, the very things that the POSH worksheet implies is not possible.


This statement is not correct. The possession of homologous structures does indeed imply descent from a common ancestor, but not necessarily a "close" one. The forelimbs of all tetrapods are homologous and support descent from a common ancestor (an implication the fossil record supports), but this does not mean their common ancestor is "close."


This statement falsely implies that Limulus, the horseshoe crab, is a crustacean in terms of body structure but a chelicerate (the group that includes spiders and ticks) in terms of "blood chemistry." In fact, systematic biologists have long considered Limulus a chelicerate on the basis of body structure, and this classification is confirmed by biochemical studies.


Actually, I am unaware of any scientists who "struggle" with this question. Had POSH thought highly enough of its readership to document this assertion, it would be possible to answer it. Unfortunately, a lack of documentation accompanies nearly every assertion in the worksheets, making a direct response impossible.

This worksheet repeats the false claim that transitional forms are absent from the fossil record:


This is absolute nonsense, as the National Academy of Sciences has pointed out. Literally hundreds of transitional forms are known documenting many of life's major evolutionary transitions. The reptile to mammal transition, to take one specific example, contains so many transitional forms that it is different for experts to agree on exactly where to drawn the line between these two major groups of vertebrates. For details, see Crompton, A. W., and Jenkins, F. A. "Origin of Mammals" in Mesozoic Mammals: the first two thirds of mammalian history, Z Kielan-Jaworowska, JG Eaton, and TM Bown, eds., © 1979, University of California Press, Berkeley, CA. Indeed, consider this characterization of the reptile to mammal transition from Mark Ridley's book Evolution (Blackwell, 1996, Cambridge, MA):


Claims that the Cambrian explosion involves the first appearance of all the major animal phyla without ancestors are not true. The "roots" of the explosion are now known to be well before the Cambrian, and several animal phyla (the Edicarian fauna) appeared more than a hundred million years before the Cambrian. See "The Cambrian "explosion": Slow-fuse or megatonnage?" Proceedings of the National Academy of Sciences, 97: 4426-4429, (2000).

Statements regarding the "difficulties" of accounting for complexity are likewise incorrect. For example, the worksheet says that "Michael Behe, a biochemist, supports this theory [intelligent design] in his book, Darwin's Black Box, based on his observation of irreducible complexity at the molecular level." Behe claims that biochemical systems are "irreducible complex," meaning that they could not have evolved and therefore must have been designed by an intelligent agent. Behe's claim is simply wrong, as even a cursory search of the biochemical literature will establish. (Papers describing the Darwinian evolution of complex biochemical systems include: JM Logsdon & WF Doolittle (1997) Origin of antifreeze protein genes: A cool tale in molecular evolution. PNAS 94: 3485-3487; SM Musser & SI Chan (1998) Evolution of the cytochrome C oxidase proton pump. J. Mol. Evol. 46: 508-520; and Meléndez-Hevia, Waddell, & Cascante (1996) The puzzle of the Krebs citric acid cycle: Assembling the pieces of chemically feasible reactions, and opportunism in the design of metabolic pathways during evolution. J Mol Evol 43: 293-303.)


Worksheet #3

This worksheet attempts to address issues of facts, theories, science, and philosophy. It makes no specific criticism of the textbook, but it badly confuses the scientific usage of the words "fact" and "theory." Theories are not speculative hunches that may some day become "facts" when scientists gather enough evidence for them. Theories don't become facts, theories explain facts. This means that in scientific terms, theories actually present a higher level of understanding than facts, an appreciation that is missing from the worksheet.



Secondary Problems

POSH claims that "The text omits discussion of unsolved problems and unanswered questions in evolutionary theory, discussion of anomalous scientific data, and discussion of alternative scientific interpretations of existing evidence. Naturally, I was interested to see what these anomalous data and alternative explanations might be, which were said to be contained in worksheets 4-6.


Worksheet 4

This worksheet repeats many of the easily-refuted claims made earlier in the document, including the lack of transitional forms in the fossil record, the assertion that animal breeding could not be a mechanism of "macroevolution" (although our text never makes such a claim), and unsupported, unreferenced allegations that "some geneticists," "some biochemists," and "some mathematicians" disagree with the scientific consensus on evolution. This is no doubt true, just as "some historians" and "some political scientists" will disagree with any statement in their fields. However, since the members of POSH did not see fit to explain who these scientists might be or to provide even a cursory reference to their disagreements, it is impossible to comment on these vague assertions.

As I have noted before, the lack of even the most cursory form of literature reference in nearly every portion of the POSH statement makes it impossible for an interested reader to learn who the unnamed "scientists" and "biochemists" might be. I do not know if it was POSH's intention to make it impossible for readers to research the sources of their claims, but the poor scholarship of their documents certainly has this effect.

Worksheet 5

Worksheet 5 makes a series of incorrect and unsubstantiated claims that are easily refuted:


Natural selection is not discredited as a mechanism of macroevolution, and I would recommend interested readers consult Gordon Bell's excellent book Selection: The Mechanism of Evolution for a detailed treatment of this very topic (G. Bell, ©1996, Chapman & Hall, New York.).

POSH's statement that "mutation reduces, harms, or restructures existing DNA" is false. Most mutations are, in fact, neutral in their selective effect. This has been recognized for more than two decades and is the subject of Mootoo Kimura's ground-breaking work on the neutral theory of selection (see "The Neutral Theory of Molecular Evolution," M. Kimura, Scientific American, November 1979, pp. 98-126). I should also point out that there are many examples in the recent literature in which the acquisition of "entirely new genetic material" has been thoroughly explained. I would recommend Cheng and Chen, 1999, "Evolution of an antifreeze glycoprotein," Nature 401: 443-444 as an recent example. Curiously, POSH's worksheet challenges students to overlook or ignore scientific findings like those in this Nature paper.

Possibly. But POSH seems to have forgotten that they are critiquing a book that readily admits: "No part of this [living] system can exist without the others. So how could the whole thing have gotten started in the first place? No one knows for certain, but scientists have offered some interesting hypotheses." (BIOLOGY, page 344). Our book correctly indicates the exact level of scientific uncertainty that POSH itself holds about the ultimate origin of life, and in their haste to condemn the text they have overlooked this.

As I have already explained, POSH's assertion that the fossil record lacks transitional species is false. As the National Academy has written: "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." (Science and Creationism, page 21. National Academy Press, 1999).

Punctuated Equilibrium POSH's repeated use of Stephen Jay Gould's hypothesis of punctuated equilibrium bears special mention here. It is especially important to understand that Gould did not claim that his ideas were:

The key to understanding this statement is the term "geologically instantaneous," a term that the anti-Darwin movement, including POSH, conveniently glosses over when invoking the punctuational description of the fossil record. What, exactly, does this mean? Once again, Gould and Eldredge have made this clear:

This statement means that appearance of "instantaneous" speciation is really just an artifact of the compression of time that takes place each time a new layer is formed in the fossil record. Another of Gould's essays makes this point abundantly clear:

In other words, the process of speciation advanced by Gould is, in fact, entirely consistent with what we understand about the observable mechanisms of evolutionary change, and entirely consistent with what is seen in the fossil record. POSH's statement therefore misrepresents Gould's theories.

It explains them beautifully. More than 20 years ago, E. O. Wilson's book Sociobiology, The New Synthesis explained how each of these examples of biological cooperation and interdependence could be explained by Darwinian evolutionary biology. Far from presenting a problem for evolution, the successful explanations of these characteristics represent one of evolutionary theory's great triumphs.

It is also quite low, but this is not how evolution occurs, and POSH should know this. Evolution is a successive process, and when a beneficial mutation occurs, it spreads rapidly throughout the population. Multiple positive mutations arise not simultaneously, but in a successive selective process, as the scientific literature documents. (See, for example, "Punctuated Evolution Caused by Selection of Rare Beneficial Mutations," Santiago F. Elena, Vaughn S. Cooper, and Richard E. Lenski, in Science 1996 June 21; 272: 1802-1804.)

Without explanation, this statement seems to refer to Richard Goldschmidt's "hopeful monster" hypothesis of evolutionary change. Our book does not make reference to this idea, and it is difficult to understand why POSH would include it as a criticism of our text.

This is a good question, and one that students might benefit from studying. Unfortunately for the ideas advanced by POSH, here's what students are likely to find from a careful study along these lines:

A non-biological cultural or political agenda seems to be behind this statement, which has nothing to do with any of the material presented in BIOLOGY, and is, obviously, entirely non-biological in character. Evolutionary theory is a biological theory, not a linguistic one, and I am surprised that POSH does not appreciate the difference. Nonetheless, the inclusion of this point in the worksheet is particularly revealing, because it demonstrates that POSH's ultimate concerns are not accuracy in science teaching, but the advancement of an agenda that has to do, among other things, with the origins of language.


Actually, the Cambrian explosion confirms, rather than denies, the pattern of evolutionary change that POSH seems to object to. Therefore it is strange to seem them ask students about the Cambrian. Clearly, a dramatic diversification of body plans occurred at this point in time, but evolutionary theory easily accommodates the notions of innovation and diversification that drove the Cambrian explosion. See Simon Conway Morris's recent article for details ("The Cambrian "explosion": Slow-fuse or megatonnage?" Proceedings of the National Academy of Sciences, 97: 4426-4429, (2000)).


Worksheet #6

This worksheet poses a number of interesting questions regarding the importance of homology in biological classification and how true homologies can be recognized and distinguished from cases of convergent evolution. In places where the worksheet poses general questions, it does a fine job:

Unfortunately, when it gets down to specifics, the worksheet contains so many misunderstanding and misstatements of biological fact that it is almost useless as an analytical or teaching tool. Some examples:

The notion that homology is determined by whether one pair of forelimbs is "more similar" than another pair is false. What biologists actually look for are the presence of shared, derived characters, not overall similarity. The suggestion statement that the "blood chemistry" (an undefined term) of humans might be more similar to snakes than dogs is false and misleading. I am puzzled as to why POSH felt it necessary to bring such false statements into this worksheet.


These animals don't posses similar skeletal features, unless the test of "similarity" is being a four-legged carnivore with a body mass of 40 to 60 kilograms. In fact, the differences in skeletal anatomy between the Tasmanian tiger the wolf are profound. They include differences in the structure of the jaw, the skull, and the auditory apparatus. The Tasmanian tiger is, in fact, easily identified as marsupial on the basis of skeletal characteristics alone. Therefore these statements are misleading at best.

These statements about the platypus are similarly misleading. The bill of the platypus is only superficially similar to the bill of a duck, and the shoulder girdle of this organism is not "reptilian" in any sense that would make it possible to classify this organism as a reptile. The body hair and mammary glands of the platypus make it very clear that this egg-laying animal is a mammal. Naturally, none of these assertions are documented by reference to the scientific literature, which makes it impossible to research the unsupported claims of POSH.


Worksheet #7


This worksheet reiterates a number of claims made by other worksheets. It invites students to present alternative answer to several questions in the Section Reviews of Biology by Miller & Levine. Some examples:

Actually, this is not true. A student who "does not believe macroevolution occurred" would likely believe that species were created simultaneously at some moment in the recent past. The fossil record, the factual fossil record, dramatically contradicts this preconceived view of natural history. POSH recommends that "philosophical presuppositions" take center stage when the fossil record is analyzed. Good scientific practice, however, demands a different standard - that the facts of natural history take precedence over those presuppositions.

I agree with POSH that a student reply of this sort must not be ridiculed or dismissed, and I challenge them to find any place in our textbook or teaching materials that calls for such disrespectful treatment of any student. However, POSH's true intentions come through quite clearly in this statement. They worry that evolution implies the absence of a Creator, and that arguments against evolution amount to support for the idea of a Creator. I and many other scientists have written at great length as to why Darwinian evolution does not contradict the idea of a Creator, and I would be glad to explain these ideas in detail. They are contained in a recent book, Finding Darwin's God (K. R. Miller, HarperCollins, New York, 1999). Neither I nor Joseph Levine would countenance disrespect of a student who voiced concern on these issues, and POSH, naturally, cannot point to anything in our text that claims otherwise.

Another statement in this worksheet asks teachers to ask a question like this, and to anticipate the answer that follows:

The worksheet asserts that Prof. Behe's book contains scientifically-valid arguments in favor of common design of biochemical systems by an Intelligent Designer. Unfortunately, this is not the case. The members of POSH might do well to examine the devastating reviews of Behe's books that have appeared in respected journals such as Nature and the American Scientist. As H. Allen Orr wrote, "[Behe's] latest attack on evolution is cleverly argued, biologically informed – and wrong." (December 1996 Issue of The Boston Review.)




Secondary Problems - Appendix 1


This Appendix purports to deal with problems of "Missing or False information in the Text." Five specific examples are given, and, incredibly, every one is incorrect.

The text never claims that life has been created by experiment. However the experiment is discussed in the text in a way that mentions the "negatives" quite clearly (Biology, page 343):

It should be clear that our text does not claim what POSH implies it does, and dutifully notes that Miller's original experiments used an atmosphere that is now thought to be unlike that on the primitive earth.

The POSH document complains that:

Unfortunately, POSH is wrong about the composition of the atmosphere on the primitive earth. Geologists believe that the ancient atmosphere most likely contained water vapor (H2O), carbon monoxide (CO), carbon dioxide (CO2 ), hydrogen (H2 ), and nitrogen (N2). It may also have contained ammonia (NH3) and methane (CH4). It did not contain oxygen gas, and thus could not have supported life as we know it. Geological evidence supports this hypothesis because rocks from this time contain almost no rust or other compounds that require oxygen to form. Source: Science 259: 920-926 [1992]

A re-reading of Miller & Urey's actual research paper shows that this claim is false. They simply ran their experiment and then analyzed, at the end of the experiment, the composition of the liquid in their experimental flask. They did not trap or filter products to "protect" them from the spark, as claimed.

I must sincerely hope that the authors of this document are not involved in science education, since any biology teacher should know that DNA and RNA are not composed of amino acids. They are in fact composed of nucleotides. Furthermore, neither Miller nor anyone else engaged in origin of life research has ever claimed that polypeptides as large as 70-100 amino acids could have assembled spontaneously.


Unfortunately, POSH is quoting from an old edition of our text. In 1996 we updated this section to more properly define vestigial organs as those whose size or function are mere vestiges (traces) of those in other organisms:

POSH also believes that our text's discussion of equine evolution is incorrect:


This statement is dramatically wrong. What has been "discredited" is Marsh's old idea that horse evolution followed a straight-line, orthogenic pathway of increasing size and perfection. We now appreciate that equine evolution followed a branching series of transformations that were entirely Darwinian in character, and we presented a detailed diagram (Figure 13-15) documenting that pattern (shown at right) beginning with the fourth edition of our text.

The rich, detailed fossil record of equine evolution has not been discredited by recent work. In fact, it has been strengthened by it. If the members of POSH are interested in the authentic evolutionary record of horses, they would do well to consult Fossil Horses (Macadden, 1992, Cambridge University Press, New York).

The statement that animal nearly identical to Hyracotherium is found alive today is laughable, especially when that animal is described as a "meat eater." Hyracotherium was a browsing herbivore. Typically, the authors of this statement do not provide a reference or even name this "nearly identical" animal.

This is not correct. A detailed analysis of recent events in the peppered moth story was posted on our book's web site during the summer of 1999. A copy of that analysis is attached to the end of this report. As the reader will see, Kettlewell was not dishonest in his work, nor has the evolutionary validity of the peppered moth story been called into question [Please refer to attached document: "The Peppered Moth - an Update].


The authors of the POSH statement fail to explain how our current understand of Haeckel's incorrect drawings came about. In August 1997 a team of British Researchers, led by Michael Richardson, discovered that a series of drawings made more than 100 years ago by German embryologist Ernst Haeckel exaggerated the similarities between the early developmental stages of vertebrate embryos. Unfortunately, Haeckel's drawings had been used by nearly all publishers as the basis for their own drawings, and therefore their textbooks (and ours) contain figures that are mistaken on this point.

What did we do when we learned of this mistake? We corrected it immediately.

Joseph Levine and I quickly prepared a web page (placed on our textbook's Internet Web Site) describing the error and showing actual photographs of the stages of embryonic development. This web page appeared in December, 1997, literally 3 weeks after I first learned of the mistake.

The Internet address of this Web Page is:

At the same time, I wrote to Prentice Hall, indicating that it was imperative we correct this mistaken figure as quickly as possible. A few months later, using photographs (not Haeckel's drawings) as the source, our publisher's artists produced the following figure, which now appears in the current printings of our text:

I believe that our actions in this particular case are indicative of the degree of personal responsibility that Joseph Levine and I take in the accuracy of our texts. Upon finding a mistaken drawing, we acted quickly and decisively to ensure that inaccurate information was corrected, and that the students and teachers who rely upon or textbooks would be given immediate access to a correction. Quite frankly, this particular objection of POSH, instead of pointing to a deficiency in our text, highlights instead our diligence in presenting students with the best and most accurate scientific information available.





The Peppered Moth - An Update


 For years the story of the peppered moth, Biston betularia, has provided one of the best-known examples of natural selection in action. The story of the moth was outlined on pages 297-298 of the Elephant Book, and highlights the field experiments of British ecologist H. B. D. Kettlewell.

However, a recent book by Michael Majerus (Melanism -Evolution in Action) makes it clear that the peppered moth story will need to be rewritten. Joe Levine and I will post a revision of pages 297-298 here just as soon as we can, but in the meantime, here is an update of what the fuss is all about:


The Peppered Moth is routinely used as an example of evolution.

But is this well-known story wrong?

The "typica" form of the moth.


The light-colored form of the moth, known as typica, was the predominant form in England prior to the beginning of the industrial revolution. Shown at left, the typica moth's speckled wings are easy to spot against a dark background, but would be difficult to pick out against the light-colored bark of many trees common in England.

Around the middle of the 19th century, however, a new form of the moth began to appear. The first report of a dark-colored peppered moth was made in 1848. By 1895, the frequency in Manchester had reached a reported level of 98% of the moths.

 This dark-colored form is known as carbonaria, and (as shown at right), it is easiest to see against a light background. As you can well imagine, carbonaria would be almost invisible against a dark background, just as typica would be difficult to see against a light background. The increase in carbonaria moths was so dramatic that many naturalists made the immediate suggestion that it had to be the result of the effects of industrial activity on the local landscape.

The "carbonaria" form.

As noted on page 297, coal burned during the early decades of the industrial revolution produced soot that blanketed the countryside of the industrial areas of England between London and Manchester. Several naturalists noted that the typica form was more common in the countryside, while the carbonaria moth prevailed in the sooty regions. Not surprisingly, many jumped to the conclusion that the darker moths had some sort of survival advantage in the newly-darkened landscape.

In recent years, the burning of cleaner fuels and the advent of Clean Air laws has changed the countryside even in industrial areas, and the sootiness that prevailed during the 19th century is all but gone from urban England. Coincidentally, the prevalence of the carbonaria form has declined dramatically. In fact, some biologists suggest that the dark forms will be all but extinct within a few decades.

For evolutionary biologists, the question behind the rise and fall of the carbonaria form is "Why?" Why should the dark phenotype have appeared so suddenly, come to dominate the population in industrial areas, and then have declined just as sharply when levels of pollution declined? To many biologists, the answer seemed obvious. In areas where pollution had darkened the landscape, the darker moths were better camouflaged and less like to be eaten by birds. Under less-polluted conditions, the light-colored moths prevailed for similar reasons.

But was the obvious answer correct? That's what Kettlewell set out to check in a series of classic studies carried out in the 1950s. As described in Chapter 14 of the text, his results seemed to confirm that background camouflage was the key:

 BIOLOGY by Miller & Levine,
page 298:

"Kettlewell found that in unpolluted areas, more of his light-colored moths had survived. In soot-blacked areas, more of the dark-colored moths had survived. Thus Kettlewell showed that in each environment the moths that were better camouflaged had the higher survival rate. It was logical to conclude that when soot darkened the tree trunks in the area, natural selection caused the dark-colored moths to become more common. Today Kettlewell's work is considered to be a classic demonstration of natural selection in action."

 However, in 1998, Michael E. N. Majerus of the Department of Genetics at the University of Cambridge carefully re-examined Kettlewell's studies, as well as many others that have since appeared. What he reported, first of all, was that Kettlewell's experiments, indicating that moth survival depends upon color-related camouflage, were generally correct:

" Differential bird predation of the typica and carbonaria forms, in habitats affected by industrial pollution to different degrees, is the primary influence on the evolution of melanism in the peppered moth."

(P. 116, Melanism - Evolution in Action, M. E. N. Majerus, Oxford University Press, New York, 1998).

However, Maj erus also discovered that many of Kettlewell's experiments didn't really test the elements of the story as well as they should have. For example, in testing how likely light and dark moths were to be eaten, he placed moths on the sides of tree trunks, a place where they rarely perch in nature. He also records how well camouflaged the moths seemed to be by visual inspection. This might have seemed like a good idea at the time, but since his work it has become clear that birds see ultraviolet much better than we do, and therefore what seems well-camouflaged to the human eye may not be to a bird. In addition, neither Kettlewell nor those who checked his work were able to compensate for the degree to which migration of moths from surrounding areas might have affected the actual numbers of light and dark moths he counted in various regions of the countryside.

These criticisms have led some critics of evolution to charge that the peppered moth story is "faked," or is "known to be wrong."

Neither is true. In fact, the basic elements of the peppered moth story are quite correct. The population of dark moths rose and fell in parallel to industrial pollution, and the percentage of dark moths in the population was clearly highest in regions of the countryside that were most polluted. As Majerus, the principal scientific critic of Kettlewell's work wrote, "My view of the rise and fall of the melanic form of the peppered moth is that differential bird predation in more or less polluted regions, together with migration, are primarily responsible, almost to the exclusion of other factors." (p. 155).

So, what's going on here?

Well, the best way to put it is that what we are seeing is the scientific process at its best. Majerus and other ecologists have carefully examined the details of Kettlewell's work and found them to be lacking. As Majerus explains, to be absolutely certain of exactly how natural selection produced the rise and fall of the carbonaria form, we need better experiments to show that birds (in a natural environment) really do respond to camouflage in the ways we have presumed, that the primary reason the dark moths did better in polluted areas was because of camouflage (and not other factors like behavior), and that migration rates of moths from the surrounding countryside are not so great that they overwhelm the influence of selection in local regions by birds. Until these studies are done, the peppered moth story will be incomplete. Not wrong, but incomplete.

What we do know is that the rise and fall of dark-colored moths, a phenomenon known as "industrial melanism," remains a striking and persuasive example of natural selection in action. What we have to be cautious about is attributing 100% of the work of natural selection in this case to the camouflage of the moths and their direct visibility to birds.