Evolutionary Pathways in Nature
By Yee, Danny
Evolutionary Pathways in Nature – John C. Avise. 2006. Cambridge University Press, Cambridge, UK. 286 pp. ISBN 0-521-85753-8, 70, US$120 (hardback); ISBN 0-521-67417-4, 35, US$65 (paperback).
There are works of popular science with enough substance that they can usefully be read by professional scientists, and there are also academic books that are accessible enough that they can easily be read by nonspecialists. Such books are more common in some subject areas than in others, however, and phylogenetics has been relatively neglected, at least in comparison with natural history or the flashier areas of evolutionary theory and paleontology.
An introduction to phylogenetic theory and methods in this vein remains to be written-the closest we have is perhaps a textbook like Page and Holmes’ Molecular Evolution-but Avise’s Evolutionary Pathways in Nature offers a broad survey of phylogenetic applications. Summarizing recent research, and moving from general context to focus on results, it is pitched at biologists working outside phylogenetics, but it is also a good fit for students, potential students, and generalists like myself.
Evolutionary Pathways explores applications of comparative phylogenetics to natural history, ethology, biogeography, taxonomy, and other areas of biology. Each of its 70 essays follows a similar pattern, giving some background to a group of organisms, posing a question about their evolutionary history, and attempting to answer that question using phylogenetic analysis. The essays are independent, with just the occasional cross-reference, and they can be read in any order.
At the heart of each essay is a phylogenetic tree, taken from the most recent studies and illustrated with a figure specifically drawn for this book. How these trees were obtained is not covered, however: the captions offer only such information as “from mtDNA gene sequences” or “based on DNA sequences from four nuclear genes,” and there is no discussion of phylogenetic methods. Nor is there any detail about the matching of phenotypic characters to extant species and the estimation of the most likely states at ancestral nodes, although an appendix explains the basic theory of phylogenetic character mapping.
The substance of Evolutionary Pathways lies not in phylogenetic theory itself but in its applications. The sections into which the essays are grouped give a feel for its reach: anatomy and morphology, body coloration, sex and reproduction, behavior and ecology, cell biology and physiology and genetics, and biogeography. It ranges from theoretical insights into these domains to more isolated facts that are nevertheless striking.
There is one essay on bacteria, exploring the origins of magnetotaxis; one on the origins and spread of the HIV virus; one on lichens; and one on the base of the tree of life, looking at DNA repair mechanisms. There are three essays on plants: on the coevolution of monkeyflowers with hummingbirds; on overseas plant dispersal in the Australian genus Scaevola, which appears to have reached Hawaii four times independently; and on lateral gene transfer between parasitic Rafflesia plants and their hosts. The other 60 essays span a huge zoological range, from shrimps to whales and from Australia to the Arctic.
Some of the conclusions are of relatively narrow taxonomic interest. For example, New Zealand’s giant extinct Haast eagle was more closely related to the small Hieraaetus eagles of Eastern Asia rather than to the more obvious candidate, the large and geographically closer Australian wedge-tailed eagle. Similarly, toucans are not just related to barbets but are actually embedded within the barbet clade. Other taxonomic questions are broader: one essay reviews the latest work on the relationship of microbats, megabats, and primates, for example.
Evolutionary Pathways covers more than taxonomy, however, with essays that range right across biology, often touching on broader theory as well as addressing specific questions: sexual dichromatism and monochromatism in bird coloring; Dollo’s law, which says that complex adaptations once lost are never regained in the same form; the possibility of a nonmonophyletic species, resulting from chirality-controlled mating in the Japanese land snails Euhadra; a possible case of Mullerian mimicry in the poisonous Pitohui birds of New Guinea; oviparity and viviparity in lizards; placentas in fish; convergent evolution in the stomach lysozymes of vertebrate foreguts; and much, much more.
A few excerpts will give the flavor of the topics:
“At least some parthenogenetic vertebrates can experience considerable ecological success despite their extinction-prone clonal nature. However, molecular phylogenetic analyses have confirmed that, in nearly every case, any ecological good fortune that a unisexual biotype might enjoy is evolutionarily fleeting.”
“The category ‘lichen/although ecologically meaningful, is not a coherent unit in terms of phylogenetic origins … the lichen lifestyle is a derived condition that emerged from multiple types of ancestral association, and … the progression is not always from aggressive parasitism to friendly mutualism.”
“Jamaican land crabs evolved their diverse adaptations for non- marine life and complex brood care over the relatively short evolutionary span of just a few million years. By contrast, pairs of marine crabs in the Atlantic and Pacific Oceans, isolated by the Isthmus of Panama for roughly the same amount of time, have remained ecologically and morphologically very similar to one another. Thus, newly available terrestrial habitats in Jamaica … must have opened novel ecological opportunities that provided an evolutionary impetus for rapid diversification.”
Evolutionary Pathways in Nature is not popular science in the narrow sense. It makes no explorations into biography and touches only very occasionally on the history of the science. Neither the title nor the term “phylogenetic character mapping” are attention- grabbing, and there is no attempt to simplify technical terminology, although a glossary is provided. Perhaps most significantly, Evolutionary Pathways is not published as popular science: it is a large-format work printed on high-quality paper, with a recommended retail price that puts it outside popular reach.
On the other hand, such brief, independent essays obviously can’t go into any technical detail, and there’s nothing in Evolutionary Pathways that a keen reader of popular biology or a bright high school student couldn’t follow. Avise’s enthusiasm is obvious, and the content is also highly accessible, with most of the essays being on vertebrates and many on “charismatic megafauna”-elephants, polar bears, yetis, and so forth. The background material is often intriguing in its own right and many of the conclusions have a strong “Wow, did you know that …” element. Although there are no photographs, there are a few attractive line drawings of some of the animals discussed. Evolutionary Pathways in Nature can be appreciated simply as an exploration of “the marvelous workings of the natural world.”
So, in some ways Evolutionary Pathways sits awkwardly between two stools: general readers may find it daunting or dry, whereas specialists may find it lacks depth and detail. There are, however, plenty of potential readers in between those two categories.
Many readers of popular science want more science and less digression. In the hands of someone like Stephen Jay Gould, each of Avise’s topics would have become an essay a dozen pages long, offering insights into the history and philosophy of science, presented with literary aplomb. That would have made a fine volume, but it would also have been three times the length without offering any more actual science; and in the hands of less skilled and knowledgeable popularizers, this kind of expansiveness can easily descend into vague, unfocused, and inaccurate meandering.
It is still possible to do a degree in biology without being exposed to much phylogenetics; and increasing specialization means that even research scientists need nontechnical reviews, summaries, and overviews to keep up with work outside their fields. Here, as a show case of the ways in which “comparative phylogenetic perspectives can contribute to the process of biological discovery,” Evolutionary Pathways may help biologists understand what phylogenetics has to offer their own research. There are no notes in the text, but the bibliography lists the sources for each essay separately; there are also pointers to works on theory and methods.
Avise’s approach is not necessarily appropriate for every subject, but it is one I think should be considered more often. If scientists can step back a little, distill key ideas and results, and write clear and lucid prose, then they can make science accessible to a broader audience without having to take on literary ambitions, become biographers and historians, or oversimplify their material.
Danny Yee, 1 McKye Street, Waverton NSW 2060, Australia; E-mail: editor@ dannyreviews.com
Copyright Society of Systematic Biologists Apr 2007
(c) 2007 Systematic Biology. Provided by ProQuest Information and Learning. All rights Reserved.