The Tangled Bank: An Introduction to Evolution

I am on the lookout for a new textbook for my non-majors Evolution course, so I was excited to check out Carl Zimmer’s new book “The Tangled Bank: An Introduction to Evolution”, published this year by Roberts and Company. For those of you who are not familiar with Carl Zimmer’s work, he is a prolific popular science writer whose clear depictions of evolutionary biology and its discoveries are featured in Scientific American,  Discover, and The New York Times. Zimmer has also written a number of books that chronicle evolution, including Evolution: The Triumph of an Idea, the companion to PBS’s Evolution series. He maintains a quality blog called The Loom.

The Tangled Bank is an interesting book, as it claims to be a textbook but gives the first impression of a book that ought to be on the shelf of the local public library. This is not an insult in the least: the ability to speak to the lay reader for whom evolution is a subject of curiosity is of unparalleled importance. But the needs of a casual-but-interested reader are different from those of an instructor charged with bringing the subject of evolution to life for non-science majors. Could The Tangled Bank serve as a textbook?

Zimmer’s renown as a writer is completely merited, as he has both the broad knowledge and exceptional clarity of writing required to successfully pull off a book of this sort. The tone of the book is spot on: conversational without seeming condescending, concise and clear yet full of intriguing content. Although I was familiar with most of the discoveries and concepts covered in the book, I found myself seeing these subjects at new angles thanks to Zimmer’s engaging narrative. I have to say that the book had me wondering about who is most qualified to write about science: those who are its chief practitioners, or those whose background is in writing.

One of the really strong features of The Tangled Bank is its ability to create an accessible interface between the reader and the process of scientific inquiry. Most evolution textbooks designed for non-majors speak broadly of discoveries and may feature a few marquee experiments, but generally do not provide much sense of how the broader field accumulates knowledge. Many more comprehensive evolution textbooks designed for majors essentially read like extended-play review papers, endlessly citing experimental results from the primary literature without feeling much burden to stop and explain. Zimmer has captured a valuable middle ground by very carefully selecting and explaining key experiments and their results, often providing the reader with figures that show these results (although see below on the overall quality of illustrations). Zimmer is also in the habit of at least naming and often acquainting us with the scientists responsible for important research, and each chapter features images of a few of these scientists. What I really like about this approach is that it gives students a much better sense of the team effort that is modern science, removing the idea that a few famous pioneers are the only scientists worth knowing about. I can see my students really enjoying the narrative stories he tells throughout the book.

Two chapters stand out as particular strong to me. Chapter Two (Biology: From Natural Philosophy to Darwin), which covers the intellectual history of evolutionary biology, is especially strong in explaining the foundation of scientific understanding that provided Wallace and Darwin with the opportunity to conceive of a comprehensive theory of evolution. At the other end of the spectrum, Chapter Thirteen (Evolutionary Medicine) allows the reader to see how all of the hard-won concepts explained earlier in the book can be applied to improve human health.

Another strength of The Tangled Bank is its overall thoroughness. It covers a hearty chunk of evolutionary biology in a manner that is up-to-date and comprehensive. It is clear just from reading the book that Zimmer does a lot of reading of his own, and a well-organized and impressive reading list is provided for those who want to pursue particular topics of interest. If I were to say that I miss one topic, it is of course the topic nearest and dearest to my heart: the evolution of cooperation. In a few scattered places Zimmer does refer to mutualism, altruism, kin selection, and multilevel selection, but these topics are not well-developed in this treatment of evolution. Were these left out to appease orthodox reviewers? Was delving into these highly-theoretical topics deemed too difficult given the target audience? These are both understandable if not defendable reasons for not having a section dedicated to cooperation, but their omission could be a deal-breaker for me. In my experience, these topics are of great interest to students because they are  applicable to their own lives, and by not confronting the balance between exploitation and cooperation this book (like many others) misses a great opportunity to expand the boundaries of student understanding. When endosymbiotic theory is not included in the section on “major life transitions”, you start to wonder…

One of the biggest questions about the viability of using this book as the basis for a non-majors course is Zimmer’s background. He neither teaches nor does research in evolutionary biology (although he does teach writing at Yale), so is he qualified to write a textbook? One of the interesting things about this book is that it maintains a set of scientific advisors, each of whom is a prominent researcher in a major area of evolutionary biology: Joel Kingsolver, Kevin Padian, Gregory Wray, and Marlene Zuk. Although it is hard to tell how each of these advisors contributed to the book, it is undeniable that their involvement lends validity to its content. Perhaps it was a comfort to Zimmer or his editor to know that the book would be vetted by the pillars of the field, but I actually trust Zimmer to get the evolutionary biology right. What I wonder is whether he knows how to provide a book that works for the non-majors classroom, an environment I doubt many prominent researchers see too often.

It is in this arena that I wonder most about the value of The Tangled Bank as a non-majors textbook. Leading non-majors through the complex conceptual landscape of evolutionary biology is an art, and if done improperly can lead to a lot of confusion. I would argue that the sequence in which topics are introduced is of paramount importance, as understanding is built sequentially by building different concepts on top of one another. At times The Tangled Bank can feel like a big list of topics (albeit compellingly depicted) rather than a coherent journey through the field.

I do not like the ordering of topics in The Tangled Bank. This might be a matter of personal taste, but I have a hard time teaching about selection on genes before discussing selection on traits, and I do not see how students can fully appreciate phylogenies until they grasp the concept of speciation. Presenting the evidence for evolution before explaining the mechanistic theories that underly evolutionary change is also a problem for me, although there are plenty who are in the “pattern before process” camp. I would never organize my class so that the concepts of natural selection and adaptation were left to the middle of the semester, but this would be the consequence of following The Tangled Bank’s idiosyncratic sequencing. It is not uncommon to be at odds with the author of one’s chosen textbook over the issue of topic sequence, and the usual solution to this problem is to just assign chapters out of order. But the integrative, non-modular approach of The Tangled Bank might make it less easy to slice and dice without putting students in the position of reading explanations that presuppose knowledge they will not have when reading the book out of order.

The weirdest decision of all was to “sprinkle” the text with elements of human evolution rather than follow the conventional route of providing a stand-alone chapter on the subject towards the end of the text. While I respect the embodied stance of this decision — that humans are just another animal so why wait to talk about them until the end — it is my experience that students benefit from waiting to consider the complexities of human evolution until after they have been given the chance to learn the basic mechanisms of evolution by considering other organisms. There is something special about human evolution — most notably our cultural evolution — and a bit of that story is lost in The Tangled Bank.

Some instructors will be frustrated to learn that The Tangled Bank lacks many of the features of a conventional textbook, especially questions at the end of each chapter. While there is a great glossary and thorough index as well as the aforementioned reference list, the chapters end rather abruptly and unsatisfactorily with some pretty sundry concept lists. For those who want the textbook author to do all the work, there is also no test bank available for instructors. I personally could do without these extras, but they contribute to the concern that this might not be a suitable textbook for most non-majors instructors. I actually had a brief phone and email conversation with Ben Roberts, publisher of the book, and he told me that the next edition will contain some of the missing aids that are usually expected to come with non-majors textbooks. That these were not included in the first edition kind of makes me wonder whether this book was initially conceived of as a textbook, which might explain the odd structure it employs. Whether the retrofit works will have to be judged when the second edition comes out.

I have some other minor quibbles with the book. While The Tangled Bank has some beautiful figures and illustrations (which Roberts and Company will make available to instructors for the inclusion in lecture presentations), some of the more technical illustrations can be confusing and the captions the accompany these illustrations (which often are needed in order to understand what they depict) are of far lower clarity than the text itself. While it is somewhat expected that an instructor might have to explain technical illustrations during the class lecture, if I used this book in my class I would prepare myself for regular student confusion.

So will I use this book in the Spring? The jury is still out. I am in the process of reviewing several other candidates, but I have to say that the available contenders are less than impressive so far. With all my objections to the sequencing of The Tangled Bank, it is quite possible that Zimmer’s impeccable prose may win me over, especially when placed next to his competitors. After all, we can only select from available variation.