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The Tangled Bank: an introduction to evolution


The Tangled Bank: an introduction to evolution
Carl Zimmer 2009. Roberts and Company Publishers

He lies there on the cover, a large mischievous fishy grin on his face, but with his un-fish-like neck and weight-bearing elbows flexed, as if ready to take a quick dash across an exposed rock as imagined by Gary Larson in a Far Side cartoon as a Great Moment in Evolution. However Tiktaalik roseae probably never did dash out on land, this proto-tetrapod most likely lived its whole life in shallow coastal waters and simply used its lobe-fins and bending wrists to move about its habitat and lift its mouth up to take a gulp of fresh Devonian air. Carl Zimmer uses this amazing creature, not only as a cover model, but to unspool a well-honed tale of evolutionary discovery and adventure. Within just a few pages, this example is expertly wielded to cast light upon how evolutionary biologists create phylogenetic trees, attempt to reconstruct the ancestral tetrapod body plan, and create detailed hypotheses based on the fossil record.

Zimmer, best known for his popular science writing and blogging, describes the details of evolution with clarity and excitement in his new introductory evolution textbook, The Tangled Bank. The text is intended ‘for those who are not planning to be biologists – in other words, most people’ and reads like a hybrid between a standard text book and a popular science piece á la Richard Dawkins or Steven J. Gould.

Opening the cover, the first thing you encounter are the eye-catching end pages, which are color-coded time scales of the history of life on earth, useful in helping to put his marvelous examples into the context of geological history.

After the contents page, Zimmer dives right into the excitement of discovery with paleontologist Hans Thewissen digging up a 49-million-year-old ‘whale with legs’ in Pakistan. The leggy whale is seen on the facing page in full color, looking much like a long-snouted sea lion about to snatch up a minishark with its huge fanged mouth. Zimmer uses this first chapter, organized around the evolution and biology of whales, to investigate ‘What Is Evolution?’ what kind of Evidence evolutionary biologists use, and finally the case study of ‘Why do Whales Have Blowholes’ which draws on fossils, morphology, genetic changes, life history, parasites, social interactions and the modern-day threat of extinction. He uses each story to illuminate many topics.

Following chapters explore Natural Philosophy up to and including Darwin segueing into Natural Selection, Fossils, The Tree of Life, Genetics and Heredity, Mutation, Drift and Selection, Genetic History, Adaptation, Speciation, Radiations and Extinctions, Species Interactions, Sexual Selection, Evolutionary Medicine and the Evolution of Behaviour. The book closes with a glossary, an index and a very solid reference section, which is divided by chapter, and then further into general references for the topic and specific references to the studies that are described in each chapter.

The first page of each chapter does a wonderful job of plunging the reader right into the action of research, from fossil hunting in Australia to the Arctic Circle, to catching lizards and deadly snakes, to shooting needles into giraffes in order to collect DNA samples, and even to measuring the gigantic sexual organs of wild Alaskan ducks! Each of these research scenarios acts as a teaser to an important example which will be picked up later in the chapter, creating a stronger narrative thread throughout.

Zimmer uses both tried and true examples, such as the beak of the finch and adaptive radiation of cichlid fishes, but also brings to the table cutting edge science from the last few years, like the discovery of Tiktaalik, announced just 3 years ago, work on the gene HMGA2, a version of a gene that has a strong effect on height which made headlines 2 years ago, to the discovery of a 1.5-million-year-old set of footprints created by ancestors of modern humans that was just announced this year.

The Tangled Bank is not the doorstop of a first year biology text book, but heftier than a paperback sized popsci book, with 350 pages full of text and illustrations. Zimmer’s writing style is simple and wonderfully readable, using clarity of words and thought with no serious equations to be seen at all. The fact that Zimmer can get across most of the complexity of the Hardy–Weinberg model simply using percentages and genotypes is very impressive. This is not to say that the book shies away from complex topics or reduces every idea to a simplified cartoon version, the complexity is well represented, but explained at a nontechnical level that a general reader could grasp.

Zimmer’s writing really shines when he is explaining the research of others in clear and easy to understand terms, effortlessly making some complex subjects comprehensible. A perfect example is how Zimmer explains scientists are ‘pinpointing some of the genes that may have helped to make us uniquely human’ in his treatment of the analysis of the FOXP2 gene. I was also impressed with an elegant summary of recent hypotheses about the evolution of the vertebrate eye, a topic that stretches back to Darwin, but one that modern evolutionary data continues to elucidate.

Although Zimmer is upfront about the textbook’s intended audience, from my perspective as an undergraduate biology instructor, I found it difficult to pinpoint how to best use this text. Nonbiology/evolution majors would definitely benefit from the captivating, but straightforward style, but I’m not sure that they will be able to build a strong mental map of the discipline without more of the structure being provided for them (see below). Without a more comprehensive examination of evolutionary genetics, The Tangled Bank is not quite sufficient for a 2nd–3rd year major’s course in evolution (granted that this is not the targeted audience). It could possibly be used as a compliment to a more rigorous Evolution text in a major’s course, but it might instead be more useful as a source of examples and case studies solely for use by the instructor.

Irrespective of the audience, what it is lacking is most of the support that comes from current advances in pedagogy. For example, there are no focus questions, no bolded key terms, and no ‘test your knowledge’ summary questions. These are many of the elements that can help add needed structure to a student wading into a discipline that is new to them. Some will find this lack of ‘hand-holding’ refreshing and will be able to build that structure into the course themselves, but many faculty members have their time so thinly stretched that they appreciate any and all teaching support that a text book can offer.

I did have a few other minor issues with the text. Zimmer takes an interesting approach to human evolution, weaving it throughout the entire book, rather than devoting a chapter to the subject. This accomplishes the goal of showing how the field can be applied to humans in the same way it can be used to explore the evolution of any other animal, but at the same time makes it very difficult to assign reading for a specific lecture on the subject. He has also decided to stick with the more traditional use of the term hominid for human ancestors, rather than the newer taxonomic term hominin, which appears to be gaining in popularity.

Also, there’s only a brief mention of the difference between positive and stabilizing selection, which seems like it should have been used in a stronger role in describing how selection works. Zimmer uses many common sense, simple analogies that should work well with his nonmajor target, like the classic pulling colored jellybeans to illustrate genetic drift, or how small differences in fitness can have magnified effects over the generations, just like monetary investments earning interest in a bank account. But in the same chapter he also has six graphs from computer simulations. These might have worked better in a lab setting, where students could manipulate values to see how the outcomes change. But these are small quibbles, most of the text and pictures do a wonderful job in getting across their point.

Overall, The Tangled Bank is an attractive and captivating book, masterfully told, but like Tiktaalik, is not really a fish and not really an amphibian. The marketplace and readers will have to decide if this new kind of hybrid text will work better in the classroom or as an entry level evolution book for the self motivated learner looking to go beyond the popsci books in their local bookstore. Readers may love the unique format, or they might end up feeling like a fish out of water, slightly disoriented from being out of their element. What is certain is that all readers will be able to immerse themselves in the captivating field of evolutionary biology as written by a master storyteller.