Reviewing a science book for high-school honors courses

BSCS Biology: A Molecular Approach
2001. 848 pages. ISBN of the student's edition: 0-538-69039-9.
Developed and copyrighted by the Biological Sciences Curriculum
Study (Colorado Springs, Colorado). Published by the Everyday
Learning Corporation, P.O. Box 812960, Chicago, Illinois 60681.

This Extensively Revised Textbook
Merits a Strong Recommendation

David L. Jameson

In this review I will describe some of the revisions that BSCS has carried out, and then I will consider how this eighth edition of the Blue Version can be used in schools.

BSCS's writers and editors have replaced about one-fourth of the chapters that appeared in the seventh edition, have reworked most of the others, and have added new sections on genetics, development, organic diversity, and ecology. Generally, these revisions have served to improve the book, the more so because the new or revised chapters generally convey accurate impressions of our current state of knowledge about the topics that they cover.

BSCS's illustrators and graphic designers have contributed some improvements too, enabling the Blue Version to carry more information. They have tightened the typography in the book's main narrative by reducing the spacing between lines, and they have reduced the book's load of non-contributing pictures, i.e., pictures that look pleasing but don't contribute to the learning of biology.

As a whole, this new edition is a much-improved text. It does a better job of covering the traditional topics of high-school biology while, as a whole, it retains the characteristics that we have come to associate with BSCS books -- accurate representations of science, delivered in straightforward declarative sentences that are appropriate, in length and style, for high-school readers. I suspect that Charles Darwin would be pleased to read this book, for the BSCS writers' sentences seldom "want translating" (to use Darwin's phrase).

The overhauled chapter about population genetics, chapter 16, has a new section on quantitative characters, and this provides a nice basis for understanding much of the variation in size, shape and pigmentation that students see when they look at each other or at various critters that they encounter in their daily lives.

The chapter that deals with development in animals has been nicely revised to include new information about HOX genes, cellular interactions and cell determination (defined as "the process by which a cell commits to a particular course of development"). The text focuses on studies of development in fruit flies and in certain vertebrates. It would be better -- and it would help students to understand the universality of some basic developmental phenomena -- if it also presented information acquired from studies of the nematode Caenorhabditis elegans, an animal whose development has been elucidated in great detail [note 2].

The new chapter on "Advances in Molecular Genetics" covers genomics, the Human Genome Project, mutation and DNA repair. (In their next edition, the BSCS writers should point out that some 32,000 genes have been identified in man, and that most of them are similar to genes that occur in every other living creature. The writers should also emphasize the fact that knowing an organism's entire sequence tells little or nothing about other aspects of the organism's biology, such as what the organism looks like, where it occurs, how it behaves, or how it makes its living.)

The writers give a page and a half to gene therapy, starting with the declaration that the treatment or prevention of genetic defects will be the most important result of the Human Genome Project, and then they bluntly introduce the student to the potential misuse of genomic data about individuals. Bravo!

In fact, social issues that accompany advances in biology are brought up at many places in the book, and the writers are careful to avoid making judgmental pronouncements. They encourage students to think about issues, but they don't require the students to make hard-and-fast decisions. They thus acknowledge, implicitly, that issues and arguments change with changes in the available information. I suspect, by the way, that students who use this book will recognize that the recent debates about the regulation of stem-cell research have been wholly political affairs, even if some of the participants have been dealing in "scientific" rhetoric. Bravo! Producing citizens who can think so clearly that their powers of perception will be terrifying to the establishment is exactly what education should do!

The chapter "Patterns of Inheritance," covering traditional Mendelian genetics, is followed by a new chapter titled "Other Forms of Inheritance." Here the major topics are epistasis, transposable elements, genomic imprinting and cytoplasmic inheritance. Those might not have been my choices, but they represent the BSCS writers' willingness to thrust the student into realms of biology where important findings are being made -- and the chapter is well done.

The two chapters about ecology have evidently been included because chapters about ecology are considered necessary in a high-school biology text. I have been disappointed to find that there is little molecular biology in the ecological material that the BSCS writers present. (In their next edition, they should tell about some of the innovative molecular approaches that ecologists now are using to solve problems.) There are other disappointments as well:

• The section called "Origin of Species," in chapter 19, nicely catalogues a variety of isolation mechanisms, but it generally fails to reveal any genetic or molecular bases for these mechanisms. Only in the case of speciation by polyploidy do the writers connect reproductive isolation with genetic events.

• On page 467 we find the categorical statement that "An individual with an altered protein would be at a disadvantage compared with other members of the population." This claim is one of various little things that have sneaked into the book and that detract from its overall accuracy and coherence. If the claim were true, evolution would hardly happen at all. Let's hope that, at least once a year, a bright student will point out that the alteration of proteins is a pivotal source of new adaptations and of evolutionary change under natural selection.

• On page 350 we read that "The HGP [Human Genome Project] is sequencing sections of DNA from many people." Maybe a student who has learned about the HGP from other sources will provide the information that, in fact, the DNA for the HGP has come from only five individuals.

There are two dozen articles labeled "Biological Challenges: Research" or "Biological Challenges: Discoveries" in which BSCS's writers try to describe some selected scientific investigations. If the writers' objective was to enable students to visualize what was done, how it was done, and what the results meant, then the writers have succeeded in only a few cases. These include the account of how Jan Baptista van Helmont analyzed vegetative growth (page 107), the account of how Joseph Priestley used a candle and a plant in experiments that suggested oxygen (page 107), the account of how Marshall Nirenberg used poly-U to achieve the first discovery of a codon (page 239), and perhaps two or three more. In most other instances, the writers provide summaries of results -- but how the results were obtained will remain mysteries to students whose only source of information is this book.

The same weakness is evident in the book's main text. The account of Spemann and Mangold's amphibian-development experiments (page 285) and the brief section about the use of auxins for manipulating the development of plants (page 302) may enable students to imagine how they might replicate those procedures -- but elsewhere the writers generally have failed to describe scientific work in ways that would allow students to understand what actually was done. Exciting (and often very simple) procedures figure in the everyday work of laboratory scientists and field scientists, but when a book describes only results and conclusions, the excitement is missed.

A crucial shortcoming of BSCS Biology: A Molecular Approach is that the BSCS writers have again failed to make a straightforward presentation of the concept of the molecular clock. Some of the elements of this concept can be found in the book, but they are scattered about and are never brought together. Yet the essential points that students must learn can be assembled and stated economically: (1) Even in the absence of selection and migration, large populations will evolve because mutations will occur continuously -- a point that was made by J.B.S. Haldane in the 1950s and then was developed by Motoo Kimura, James Crow, Masatoshi Nei, and their students and followers. (2) Analyses of mutations lead to phylogenetic trees of molecules. (3) Different molecules evolve at different rates, and different parts of a given molecule may evolve at different rates. (4) Changes in rapidly evolving molecules, such as the fibrinopeptides, can be used to discern relationships among taxa in the lower taxonomic categories (i.e., species, genera and families), while changes in slowly evolving molecules, such as the histones, can be used to elucidate relationships among taxa in the higher categories (e.g., orders and classes). (5) Within a category, the amount of difference between a molecule seen in one taxon and the corresponding molecule seen in another taxon should be proportional to the amount of time that has passed since the two taxa diverged and began to evolve separately. (6) Rates of molecular evolution can be affected by changes in population size, by migration, and by natural selection. Getting these points across to students doesn't require much chemistry or mathematics or theoretical biology.

In the index of BSCS Biology: A Molecular Approach, the entry for "molecular clock hypothesis" directs the reader to a "Biological Challenges" article (on page 473) about the classification of the giant panda, but that article doesn't do the job. Neither does the small boxed item about "Measuring the Rate of Evolution" (on page 513), though it helps by providing the information that different parts of a molecule can evolve at different rates [note 3]. In their next edition, the writers should provide an integrated article about how molecular clocks are used for estimating the ages of taxa -- an article at least as good as the one that tells how isotopic clocks are used for determining the ages of rocks and fossils (page 442). Without an understanding of molecular clocks, students cannot adequately compare and evaluate the three methods of constructing evolutionary trees, cannot understand when each method is useful, and cannot rationally approach the current question of whether the living world comprises six great divisions (kingdoms) or five great divisions or only three.

Finally, I note that section 18.1 ("The Species Concept") and section 18.2 ("Classification and Homologies") are not integrated, as they surely should be, with section 20.3 ("Comparing Molecular Evidence"). Section 20.3 includes an illustrated comparison of two evolutionary trees -- one based on anatomy, the other based on molecular data.

Whatever the answers to those questions are, BSCS Biology: A Molecular Approach may well be the right textbook for use in teaching biology to 10th-graders who are very bright, who can handle more science than regular high-school texts provide, and who perhaps will take, in grade 12, advanced-placement courses based on college texts. However, this book itself is not appropriate for use in an AP course. If AP students already have taken 10th-grade biology, whether in a conventional course or an honors course, they will be bored by this book because much of it covers 10th-grade topics. When students have to study the same material twice, boredom happens -- as I learned, the hard way, while teaching biology to college students who already had used college texts in advanced high-school courses.

Notes

1. E-mail message of 8 December 2000 from Rodger Bybee, executive director of BSCS, to the editor of The Textbook Letter. [return to text]

2. The BSCS writers are aware of such studies and briefly mention them elsewhere in the book: In discussing the sequencing of genomes, they correctly say that "The first multicellular organism sequenced was a tiny worm, Caenorhabditis elegans . . . . This animal has only 959 cells, and the fate of each cell during development from zygote to adult worm has been mapped out . . . ." [return to text]

3. The writers say that the rate of change for the functional part of a protein is generally slower than the rate for a less important region of the molecule, and they give an example: "For instance, the rate of evolution in the surface parts of the hemoglobin protein is 10 times greater than the rate of change at the site where the protein binds to heme." [return to text]

David L. Jameson is a specialist in molecular biology and a senior research fellow of the Osher Laboratory of Molecular Systematics at the California Academy of Sciences (in San Francisco). His published works include books on evolutionary genetics and the genetics of speciation.

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