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332 10 Systematics and Classification
in 1959. Therefore only a summary of his findings is included in the book, Animal
Species and Evolution (Mayr 1963b: 398 and Fig. 13-9). S.J. Gould later continued
the study of Cerion snails and summarized his findings in his recent book (2002).
Two Empires of Organisms or Three?
The difference between a Hennigian cladification and a Darwinian classification
underlies the argument between a group of microbiologists and Ernst Mayr (1990o,
1991h, 1998c) regarding the basic structure of the living world. There are two major
groups of organisms, the prokaryotes (bacteria) and eukaryotes (organisms with
nucleated cells). The bacteria comprise the eubacteria and the archaebacteria from
which latter group the eukaryotes derived an important part of their genome. In
reliance on the joint possession of derived (synapomorphous) characters and ignoring
autapomorphous characters the microbiologist C. Woese established three
groups (“empires”): (1) the eubacteria, (2) archaebacteria and (3) eukaryotes. Mayr
pointed out that the acquisition of nucleus, chromosomes and other characteristics
by the eukaryotes was perhaps the most important evolutionary event in the
whole history of life, separating the prokaryotes (all bacteria) from the eukaryotes.
Moreover, genetic studies showed that eubacteria and archaebacteria are far more
similar (i.e., more closely related) to each other than the archaebacteria are to the
fully evolved eukaryotes. The principle of balance clearly favors combining eubacteria
and archaebacteria in the empire Prokaryota. There is a huge gap between
these and any protist, plant or animal belonging to the Eukaryota. Their world
is entirely different from the world of the two kinds of bacteria, the Prokaryota
(a “paraphyletic” group under cladistic principles). According to Mayr (1998c)
only a two-empire classification correctly reflects the structure of the living world
(see also Mayr 2001f: 45–46).
Zoological Nomenclature
It is largely unknown that for many years Mayr was one of the leaders in this
neglected and little respected field—the system of scientific names applied to taxonomic
units of extant or extinct animals. Most of those zoologists who showed
an interest were occupied only with the paragraphs of the rules, and not with
the basic meaning of the Code of Nomenclature and its rules, i.e., conveyance of
information. Eventually Mayr was deeply engaged and developed what one might
call a philosophy of nomenclature, publishing actively in this field during the 1950s
and 1960s (Fig. 4.2). His main concern has always been the stability of names under
which animals are known. The names are more important than the nomenclatural
rules. According to his recommendations the International Commission of Zoological
Nomenclature approved, at the XIVth International Congress of Zoology
at Copenhagen (1953), a Preamble of the Code of Nomenclature stating that its
primary aim is “to promote stability and universality in the scientific names of
animals, and to ensure that each name is unique and distinct.” The whole purpose