Reviewing a science book for high-school honors courses

Biology
Fourth edition, 1995. 1108 pages + appendices. ISBN: 0-03-015434-0.
Saunders College Publishing, 150 South Independence Mall West,
Philadelphia, Pennsylvania 19106.

Though It Has Some Faults,
This Is a Solid Biology Text

Susan Singer

The book has seven major parts, titled "Cells," "Information Coding and Transfer," "Evolution," "Diversity," "Animal Biology," "Plant Biology" and "Ecology."

Part One, "Cells," includes several chapters that deal with molecular biology and are illustrated with helpful figures. The coverage seems adequate, though the level of detail may not be satisfying to the most advanced students.

In Part Two, "Information Coding and Transfer," Mendelian genetics is presented in chapter 15, which includes a brief explanation of the principles of probability. There is a section about mapping (enough to enable students to solve some very simple linkage problems), and the quiz at the end of the chapter has been appropriately expanded to provide a reasonable collection of practice exercises.

Table 15-1 purports to show the seven pairs of traits that Mendel used in his work with the garden pea, but one pair -- "axial flowers" versus "terminal flowers" -- is spurious. The trait that Arms and Camp call "terminal flowers" was most likely a mutation that resulted in odd floral configurations at the tips of stems. As far as we know now, there is no single, recessive allele, in the pea, that results in true terminal flowering and the elimination of axillary flowering.

The next chapter, "Inheritance Patterns and Gene Expression," is particularly effective because it combines classical and molecular genetics with some current, real-life applications. This chapter and the one on genetic engineering (chapter 13) stand out as engaging, balanced presentations that make science relevant while providing the student with a solid base of knowledge.

Arms and Camp approach evolution in a knowledgeable manner and view it as a broad concept, rather than as mere changes in the frequencies of alleles. They are careful to point out that natural selection is an important agent of evolution, but not the only one.

In chapter 17, "Evolution and Natural Selection," and chapter 18, "Adaptation and Coevolution," the authors use engaging examples and illustrations that should help to rouse students' interest. Chapter 19 covers population genetics, but I have seen better presentations of the Hardy-Weinberg law. The authors should have used a Punnett square to help students connect the Hardy-Weinberg equations to the genetics that the students already have learned.

Part Four, "Diversity," introduces cladistics as a way of understanding relationships among the diverse organisms that evolution has produced, but the authors have not developed this topic adequately. In particular, they should have included an explanation of how outgroups are used in determining whether characteristics are ancestral or derived.

Life cycles are nightmares for many new students of biology. Arms and Camp use life-cycle diagrams that do not bury essential points in excessive detail. Their generalized diagram of the haplodiplontic cycle (near the beginning of chapter 27) is quite helpful, but would be even more useful if the authors had also compared and contrasted the haplontic and diplontic cycles as such. Likewise, the authors' treatment of meiosis would be better if they had taken care to explain where meiosis occurs in the life cycles of different organisms. Many students acquire the misconception that meiosis must always lead directly to the production of gametes. In plants, meiosis is followed by mitosis that yields a multicellular haploid; then the multicellular haploid makes gametes by mitosis.

The chapters on the biology of plants are generally accurate, but they fail to give good explanations of exciting developments that we have seen during the past decade. On page 997, for example, Arms and Camp mention that Arabidopsis has become "the workhorse of molecular embryology in plants," and there is a table that lists some Arabidopsis mutants. Diagrams of the mutant phenotypes would be more engaging and useful. When tissue culture is mentioned as a form of vegetative reproduction, the only picture shows a researcher looking at some barely discernible plantlets. Students would gain a much greater appreciation of tissue culture if they could see a series of pictures showing regeneration at different stages.

The book's last chapter ("Human Ecology and Natural Resources," chapter 50) has a section about the Green Revolution but contains no discussion of the impact of recombinant-DNA work and transgenic plants on agriculture. This seems curious. (Information about transgenic plants appears in chapter 13, "Genetic Engineering," which falls between a chapter on animal development and a chapter on eukaryotic cells.)

In contrast, the authors' presentation of photosynthesis is excellent -- one of the best photosynthesis chapters I have seen. The energetics of photosynthesis is placed in a context of leaf morphology, the chapter includes an anatomical tour of a leaf, and the authors show how anatomical form reflects biochemical function in both C₃ and C₄ plants. They also present a short section about crassulacean acid metabolism and the advantage that this mode of photosynthesis provides in very dry habitats.

Each chapter has a summary that repeats the chapter's key points in a few terse, well focused statements. Among the end-of-chapter "Self-Quiz" questions, some ask for nothing more than iteration while others demand higher-order thinking. There are "Questions for Discussion" too, which may be useful in some classrooms, but a few of the questions are over the top. In chapter 20, for example, question 9 asks: "How might the invention of birth-control methods and labor-saving household appliances affect the monogamous mating system of humans?" Then question 10 challenges students to devise ways of determining whether there are genetic bases for certain forms of behavior:

1. In nonindustrial societies, infants are most often killed by parents for the following reasons: (1) doubt that the child is the parent's own, (2) conviction that the child is weak and unlikely to produce offspring as an adult, and (3) external pressures such as food scarcity . . . .

2. In industrial societies, parents are more likely to kill infants than to kill older children.

3. Mothers are more likely than fathers to kill infants.

4. Disproportionate numbers of child killings are by stepparents.

This Book's Sleepy Authors
Have Missed the Revolution

Terrence M. Gosliner

In the preface to this fourth edition, the authors say that they have pursued several goals, one of which is to strengthen their book's conceptual treatment of evolution. This is a laudable goal indeed.

Later in their preface, as they discuss some specific features of the new edition, they say that they have furnished a detailed description of "the revolution in the way we classify organisms, embracing cladistic methods." That claim, though, is not borne out. Despite the authors' good intentions, their brief account of "cladistic methods" includes misunderstandings, inconsistencies, and some examples and explanations that are just wrong. Moreover, these authors (like many others who have written biology texts in recent years) have treated cladistic classification as a sideshow: They have tried to describe it, in an isolated passage, but they haven't incorporated it into the rest of their textbook.

This warrants some detailed discussion, because cladistic analysis has fostered deep changes in classification and comparative biology. Teachers need better information about the cladistic approach than Arms and Camp have been able to provide, so I shall try to give some correct information here.

Our classifications will come to be, as far as they can be so made, genealogies; and will then truly give what may be called the plan of creation. The rules for classifying will no doubt become simpler when we have a definite object in view. We possess no pedigrees or armorial bearings [to guide us]; and we have to trace the many diverging lines of descent in our natural genealogies, by characters of any kind which have been inherited.

Darwin was quite right. Systematists soon began to rebuild their science on an evolutionary foundation, and they applied themselves to the task of classifying organisms into groups that presumably would reflect the organisms' genealogies. In defining the groups, however, they continued to rely upon a traditional technique that antedated Darwin and had been used since the time of Linnaeus: They constructed groups by observing apparent similarities and differences among organisms, then judging which similarities and differences should be considered the most significant.

This way of doing things -- which we may call classical systematics or evolutionary systematics -- prevailed into the 1960s. Then it was seriously challenged by two other approaches: phenetics and cladistics.

The pheneticists thought that classical systematics was too subjective and arbitrary, because it required the observer to decide which similarities and differences were important and which ones were not. The pheneticists suggested that classification should be separated from hypotheses about how organisms are related to each other, and they said that organisms should be grouped according to "overall similarity."

The cladists asserted that classification should reflect phylogenies (or genealogies, as Darwin had called them), just as in classical systematics. But the cladists, like the pheneticists, rejected the classical systematists' idiosyncratic methods. If we want to divide organisms into phylogenetic (or "natural") groups, the cladists insisted, the best way to do this would be to concentrate on derived features.

A derived feature, in any organism, is one that has arisen by modification of some earlier feature which was present in the organism's ancestors. If two organisms share a set of derived features, the organisms are likely to have descended from the same ancestral stock -- and this idea, the cladists said, should form the basis for all attempts to trace phylogenies. They contended that by focusing on the presence or absence of derived features, instead of trying to make subjective appraisals of countless similarities and differences, we could avoid many of the difficulties and ambiguities that classical systematics presents.

Cladists also insisted that every natural group must be monophyletic, meaning that it must include all the descendants of a common ancestor, as well as the common ancestor itself, while excluding everything else.

These bedrock precepts of cladistics had been set forth in a book that the German entomologist Willi Hennig published in 1950. Hennig's ideas were largely ignored outside of northern Europe, however, until an English translation of his book was issued in 1966, under the title Principles of Systematics. (Arms and Camp give Hennig's first name as "William," but that is incorrect.)

Cladists, pheneticists and classical systematists waged their philosophical warfare in professional journals and at scientific conferences for nearly two decades, until the cladists largely prevailed. Today, cladistics has emerged as the most acceptable means of constructing hypothetical evolutionary trees and using such trees for classifying organisms.

(I think that Darwin would have been amazed if he could have known that a full century would elapse between the publication of his book and the advent of substantive changes in the way classifications are constructed to reflect genealogies.)

Pheneticists advocate an artificial system of classification. They argue that we can never be certain that a phylogeny is correct, and therefore we should not even try to base classification on phylogeny. Instead, organisms should be classified for convenience, as we classify books in a library, according to their similarity to one another . . . . Thus, organisms that resemble each other closely should be grouped together, even in clear cases of convergent evolution from unrelated ancestors.

The first three sentences correctly describe the pheneticists' basic argument, but the last sentence has two flaws. First: Most biologists agree that life on Earth has originated only once. This means that all of the ancestors of all living things are related at some level, and that "unrelated ancestors" don't exist. Second: In a phenetic context, the phrase "clear cases of convergent evolution" is meaningless. If (as the pheneticists claim) we can never be certain about phylogenies, then the we can never be certain that we are looking at convergence.

Arms and Camp go on to say that "Phenetic criteria are used to classify bacteria, because the phylogeny of most bacteria is not known." This is highly misleading; the authors do not disclose that, besides phenetic schemes for classifying bacteria, we have some cladistic hypotheses about how various bacteria are related to each other. It would be better to tell students that there is no consensus about relationships among bacteria, and that the students themselves may someday want to take part in investigations of such relationships.

When they turn to classical systematics, the authors say that classical systematists seek classifications which "simultaneously reflect genealogy (common ancestry) and genetic relationships (shared characters)." This use of the term genetic is misleading. Shared characters are the entities on which genealogical hypotheses are based. Shared characters have little or nothing to do with genetics (beyond the fact that characters are expressions of genes), and I don't understand why the authors have used genetic in this context.

Next, Arms and Camp tackle cladistics, but they confuse genealogy, genetics and the concept of the monophyletic group. When they try to explain that concept, they get things wrong -- and they show little understanding of how to construct a cladogram (i.e., the kind of diagram that cladists use for depicting phylogenies based upon derived features).

On page 466 Arms and Camp tell us that birds and reptiles have a common ancestor, and that birds and reptiles therefore constitute a single monophyletic group. But then -- on page 467 -- a purported cladogram entitled "Cladistic classification" shows this bird-plus-reptile assemblage to be paraphyletic, not monophyletic. A paraphyletic group is one that includes only some -- not all -- of the descendants of a common ancestor. The rules of cladistics prohibit paraphyletic groups, and cladists do not accept them as legitimate. This is why, for example, cladists do not accept the group that the classical systematists call "fishes." This group is paraphyletic: It includes some of the descendants of an ancient vertebrate that had jaws and limb girdles, but it does not include all such descendants. [For a diagram showing a cladistic classification of the vertebrates, see Kevin Padian's article in The Textbook Letter, November- December 1993.]

Arms and Camp's illustration on page 467 also indicates that the birds and reptiles share a common ancestor with mammals. If that is true, then the monophyletic group that includes birds and reptiles should also include mammals, but Arms and Camp do not seem to grasp this. Their illustration is not consistent with what they say in their text, and it does not represent current thinking about the phylogeny of the amniotes.

The authors finish their flirtation with cladistics, on page 469, by trying to show cladistic diagrams of three historical hypotheses about the phylogenies of humans and the anthropoid apes. The first diagram is a legitimate cladogram, in that it shows the Anthropoidii to be a monophyletic group. In the two other diagrams, the anthropoids are paraphyletic and hence do not constitute a valid group.

And that is the end of that. After telling the student that cladistics is the best thing since sliced bread (which it is), the authors completely ignore cladistic principles when, in the rest of their book, the present a multitude of diagrams that supposedly depict evolutionary relationships. Arms and Camp talk the talk, but they don't walk the walk.

Perhaps the most egregious example of how these authors have failed to honor contemporary biological thinking comes when they address the subject of dividing living things into distinct kingdoms. They present the obsolete five-kingdom scheme, and they tell one reason why it is flawed: The kingdom Protista is not monophyletic and therefore is not a natural group. But then they cave in to tradition, attempting to justify the continued use of the five-kingdom scheme by noting that this scheme is convenient, even if it isn't natural!

By paying lip service to cladistics, the authors have tried to make their book seem up-to-date. In fact, however, Arms and Camp are still trapped in a conceptual framework that contemporary biology has discarded, and their failure to deal seriously with contemporary classification and today's comparative biology has me up in arms. These authors are clearly in the wrong camp.

Postscript: Science educators who want to learn more about the principles and implications of cladistics should read The Compleat Cladist: A Primer of Phylogenetic Procedures, by E.O. Wiley, D. Siegel-Causey, D.R. Brooks and V.A. Funk. It can be ordered from the publications division of the Museum of Natural History, University of Kansas, Lawrence, Kansas 66045 (telephone: 913-864-4540).

Susan Singer, a professor of biology at Carleton College (in Northfield, Minnesota), specializes in the developmental biology of plants, and she has chaired the Education Committee of the American Society of Plant Physiologists. Her current research focuses on the developmental genetics of flowering in the garden pea.

Terrence M. Gosliner is a zoologist, a specialist in the biology of marine invertebrates, and a staff scientist at the California Academy of Sciences, in San Francisco.

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