The Character Concept in Evolutionary Biology edited by Gunter Wagner, Academic Press, $79.95, ISBN 0127300554
A LOT of time and energy is going into investigating the relationship between evolution and development. 杏吧原创s want to understand how changes in the development of organisms caused by changes in gene activity can account for the evolution of the enormous variety of animal forms. A key question is, are all the different shapes of animals due to changes in just a few small groups of genes or modules?
Early on, Gunter Wagner defines a 鈥渃haracter鈥� as any structure or function in an organism governed by a gene or group of genes, such as eye colour. But lengthy discussions of the nature of characters add little to his original definition. 鈥淲hat is a part?鈥� asks one chapter, while another deals with homology and DNA sequence data.
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But there are rewards. You鈥檒l find some very interesting information buried here. For example, skull shapes in cichlid fish vary enormously both within individuals and species. This raises the fascinating question of whether a highly plastic trait can be conserved during evolution.
Be warned that much of this book is highly technical. For example, researchers ask if it鈥檚 possible to study the adaptation of individual parts more or less independently of the rest of the organism. You鈥檒l need a good grasp of advanced mathematics even to understand this question. I found much of this difficult to follow.
The second half of the book gets back to development and genetics. Are eye spots on butterfly wings a character? There鈥檚 an investigation of the genetics of quantitative traits, such as how the number of bristles varies in the fruit fly, and whether a single gene controlling several different traits (pleiotropy) is responsible for the form of the mandible. This raises a central question: do patterns of pleiotropy evolve so that related characters share a common set of genes? This might help us to understand how muscles and tendons evolve in relation to bones to give a functioning limb.
The extent to which the limbs and segments of arthropods are based on modular elements is another important issue. But the writers seem to prefer philosophical issues, rather than concentrating on the developmental processes themselves and the genes that control them. How can one mutation in the fly convert an antenna into a leg?