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322 10 Systematics and Classification
Part 1 (60 pages) of the first edition of this textbook includes brief discussions
of “new systematics,” of taxonomic categories and concepts, species and lower
categories, classification and the higher categories. While it is the function of the
species to denote distinction, it is the function of the genus to denote association.
The (subjective) genus is a systematic category including one species or a group
of species of presumably common phylogenetic origin, separated by a decided
gap from other similar groups. Part 2 (140 pages), the largest portion of the
book, introduces the reader into various taxonomic procedures (techniques of
collecting, identification and discrimination, quantitative methods of analysis, and
presentation of the results). Part 3 (80 pages) comprises treatments of zoological
nomenclature, its historical and philosophical basis, the principle of priority, the
type method and the names of systematic categories.
The text of the second version (1969b) by Mayr alone is thoroughly reworked
and represents virtually a new book. It includes discussions of the species category,
polytypic species taxa, the higher categories, and theories of biological classification,
methods of zoological classification (identification, analysis of variation,
procedures of classifying and taxonomic publications). Part 3 of the book presents
the International Code of Zoological Nomenclature. Its entire revised edition of
1964 is accompanied by much more detailed interpretations of the Rules than in
the Code itself. Most of the text is updated, incorporating a large part of recent literature.
Problems at the species level are treated with frequent references to Mayr’s
Animal Species and Evolution (1963b). The sections on quantitative procedures and
methods of illustration as well as the section on zoological nomenclature are more
condensed than in the first edition. New material includes recent developments in
taxonomic theories of classification on which Mayr (1965b,k, 1968j) had published
before: (1) Phenetics or numerical taxonomy is dismissed because important and
unimportant characters are not distinguished and because of the arbitrary levels
of phenetic distance on which phenetic categories and the delimitation of taxa are
based. (2) Cladistics: The grouping of taxa is based on the inferred branching pattern
of phylogeny determined through the distribution of derived (apomorphous)
and primitive (plesiomorphous) characters. The interpretation of character polarityiscriticalinthisanalysiswhichMayrpraisedasasoundwayofestablishing
the phylogenetic (branching) pattern of groups of related species. He criticized,
however, cladistic classifications based exclusively on branching or splitting events
without taking into consideration different rates of phyletic evolution after splitting
of the daughter species (autapomorphies). This is simply not part of the concept
of cladistic classification and thus ignored. (3) Evolutionary classification: Taxa are
delimited according to common ancestry and subsequent divergence, classification
is based on the dual results of speciation (cladogenesis) and phyletic evolution
(anagenesis) of organisms. It represents a synthesis or compromise of the best of
the two more extremist schools of thought (Fig. 10.1). Established groups should be
monophyletic (following the definition of Simpson, i.e., derived from the nearest
common ancestor); their rank in classification (genus, subfamily, family) is then
assigned on the basis of overall similarity or total information content of weighted