Reports of the National Center for Science Education
September 17, 2008
Cladistics: A Practical Primer on CD-Rom
Peter Skelton and Andrew Smith
accompanying booklet by Neale Monks, 80 pages, Cambridge: Cambridge University Press, 2002.
Alan Gishlick, Gustavus Adolphus College
Teaching cladistic methodology has always been a challenge, especially if you want to present an in-depth introduction to the topic as opposed to a brief overview. One of the standard sources for teaching cladistics in upper-level systematics classes was The Compleat Cladist (Wiley and others 1991). That book, however, has long been out of print, and unless you wanted to send your students to a used book dealer to find a textbook, there were few decent choices other than photocopies and primary literature.
With the publication of the Cladistics CD-ROM and booklet, there is now a good introductory resource on cladistics available for teachers. The CD-ROM is meant to be the main teaching source and can be used on its own; the booklet, by itself, can also serve as a good stand-alone text. The descriptions are clear and easily understandable in both media, with the booklet helping to elaborate the concepts presented in the CD-ROM. Used together, they constitute perhaps the best widely available resource for teaching introductory cladistics.
The booklet is meant as a companion for students using the CD-ROM to learn the basics of cladistics as well as the way phylogenies are computed. Its five chapters are well-organized, progressing logically from the very basic concepts behind cladistics to defining characters and character homology, generating cladograms, and testing the robustness of those cladograms, and finally to a practical hands-on exercise that allows the student to generate both molecular and morphological trees of several species of echinoids and to compare the results of the analyses.
The booklet has an excellent introduction to parsimony, and it goes through a series of complex topics with clarity and simplicity. It has a very clear introduction and explanation of molecular-based cladistics absent from previous texts. I do wish that there were more of a focus on morphological characters at the beginning. It contains an excellent discussion of homology and homoplasy in respect to pleisiomorphy and synapomorphy. It also offers perhaps the clearest discussion I have read for determination of homology in molecular data.
The CD-ROM is both informative and interactive. It is especially useful for teaching about molecular characters. The final section gives the student the opportunity to code characters from raw morphological and molecular data and then perform the analysis with the aid of the CD-ROM.
The chapters in the CD-ROM are interspersed with interactive exercises that test the student’s understanding of the various concepts as they are presented. I found them to be, on the whole, rather good. There were a few places where the exercises were not quite clear. Although the CD-ROM gives the student a chance to create matrices from raw morphological and molecular data, I think that there still is a lot of value in working out the transformation series the old-fashioned way, by hand. That is how to acquire a real understanding of what modern computer programs for cladistics are doing inside the “black box”. So there is room for improvement in the exercises, but otherwise I have no problem with them. Indeed, I think that more exercises, especially in the booklet, would be useful.
Perhaps the biggest problem with the CD-ROM is the narration. The text of the CD-ROM is spoken in a rather stuffy and pedantic British accent, which cannot be turned off. This conjures visions of American students sitting in their computer labs imitating the voice in horrible American British accents, saying things like “These parsimony criteria are jolly good.” I mean no offense to speakers of the Queen’s English, whose accents I generally find to be quite pleasant; however, in this case, I could have done without. I have no idea how British students may perceive the narration, but for Americans, the ability to replace the narration with a more familiar accent or at least on-screen text would be a welcome addition to the CD-ROM. Of course, such a minor point should by no means deter both students and teachers alike from acquiring this excellent introduction to a very important topic in the modern life sciences.
Overall, Cladistics is an excellent resource for learning the methods that are universal in systematics today. The booklet is an excellent learning resource useful for students in systematics classes or for people who wish to learn the methods of cladistics for themselves. The interactive CD-ROM exercises provide good hands-on activities, and the focus on molecular methods is invaluable, given their significance to current phylogenetics. Now if only there was a way to turn off the stuffy British narration ...
This version might differ slightly from the print publication.