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BOOK REVIEWS Functional Morphology of the Evolving Hand and Foot. By O. J. Lewis. Oxford: Clarendon Press, 1989. Pp. 359. $125. Contemporary evolutionary biologists who study the limbs of tetrapode generally do so from two perspectives. One group examines morphology for characters that may be useful in working out phylogenetic relationships. The other tries to reconstruct function for its intrinsic interest and for the insights it may yield into patterns of behavior. Of course, neither group works in isolation. A good systematist takes function into account in order to assess the phyletic stability of a character, the interrelationships of character suites, and the relative weight he may give a character on the basis of the two preceding factors. A conscientious functional morphologist looks at phylogenetic relationships because an extinct organism under study may harbor functional similarities with either related extant taxa that are experimentally accessible or better understood extinct taxa. These two perspectives have eclipsed a much older, and quite valuable, tradition of reconstructing structural/functional homologies and morphoclines. A classic example, from the axial skeleton, is the transformation of primitive synapsidjawjoint and lowerjaw into the mammalian middle ear. In this approach, strict adherence to cladistic taxonomy is not necessary to reconstruct transformation series. One needs to pay close attention to primitive versus derived character states, but these can be identified only given a broad understanding of phylogenetic relationships. In his remarkable monograph, O. J. Lewis has added a noteworthy chapter to the study ofevolutionary morphoclines. With primates as a focus, he has lovingly traced the history of the bones, ligaments, and muscles constituting the forearm, hand, leg, and foot. This is not simply a compilation of the many papers that Lewis has published over the last 3 decades; there is much new information. Moreover, the work is written as a grand synthesis, a seamless treatise in which morphology, function, and evolution are splendidly interwoven. In tracing the evolution of the distal limb segments, Lewis uses an admirably synthetic approach to determine homologies. While relying primarily on comparative anatomy, he supplements this with data from paleontology, embryology , and intraspecific variation. The last yields instructive atavisms and anticipations (as well as numerous misleading neomorphs). He shows that the most secure hypotheses are supported by congruent lines of evidence from all these data sources and recognizes the pitfalls of relying on a single body of data, citing Permission to reprint a book review printed in this section may be obtained only from the author. 152 Book Reviews several studies in which carpal and tarsal homologies were incorrecdy attributed on the basis of vague mesenchymal condensations in human embryos. Multiple criteria are used for establishing character homologies. These include topology, inter- and intraspecific morphoclines, and ontogenetic character precedence. He generally rejects the use of patterns of nerve supply to deduce the homologies of muscles, regarding these as too plastic. Lewis cautions his readers that it is necessary to establish homologies at each grade of major reorganization (e.g., rhipidistian, synapsid, cynodont, mammal, therian, placental) before moving on to the next most derived grade. Jumping directly from lobe-finned fish to human (and this has been attempted!) is fraught wtih uncertainty. In establishing character polarities (i.e., primitive vs. derived characters), Lewis again uses a range of different criteria. I support this, but Lewis is somewhat sloppy in the use of some of them. His applications ofoutgroup analysis are not rigorous and are sometimes downright arbitrary. To reconstruct the primitive morphotype for the synapsid ancestors of mammals, he often relies only on the rhyncocephalian Sphenodon. For the forelimb especially, he usually chooses only few representative marsupials and placentals that appear to him to be primitive, and then pronounces the skeletomuscular morphology primitive on that intuitive basis alone. Moreover, different taxa are often used to establish the primitive morphotype for each anatomical unit, producing a lack ofcomparability between units. Within primates, he implicitly places great weight on the somewhat hazardous criterion of in-group comparisons—in other words, trusting that the wider a trait is distributed, the more likely it is to be primitive. To root his morphoclines (i.e., to establish their direction), Lewis often uses an unstated weighting system based on the likelihood...

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Additional Information

ISSN
1529-8795
Print ISSN
0031-5982
Pages
pp. 152-154
Launched on MUSE
2015-01-07
Open Access
No
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