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204 5 Biological Species and Speciation—Mayr’s First Synthesis
limited. (Regarding Mayr’s conceptualization of typological versus population
thinking since the late 1940s see p. 350.) 7
(2) The biological species concept states that a species is a group of interbreeding
natural populations that is reproductively (genetically) isolated from other
such groups because of physiological and/or behavioral barriers; the limits of
biological species are open.
Other “species concepts” proposed are those of the “vertical” (historical) cladistic
“species” (W. Hennig) and of the paleontological or evolutionary “species”
(G. G. Simpson) which, however, refer to portions of phyletic lineages rather than
species (see p. 213). The “chronospecies” of paleontologists, i.e., artificially delimited
subdivisions of phyletic lineages, are not species in the sense of biological
species. Mayr (1942e: 154) stated: “The ‘species’ of the paleontologist is not necessarily
always the same as the ‘species’ of the student of living faunae.” The
recognition concept is a different formulation of the biological species concept
(Mayr 1988h). Under each of these as well as the typological and biological species
concepts mentioned above authors delimit narrow, intermediate or wide species
taxa, depending on whether they place the taxonomic species limits at relatively
low, intermediate or rather high levels of differentiation among the geographically
representative populations, respectively. Narrow species limits emphasize differences,
wide species limits emphasize similarities among the various geographically
representative taxa. The so-called phylogenetic species concepts are instructions of
how to delimit particularly narrow species taxa, but not theoretical species concepts.
Hey (2006) reviewed the long-standing discussion on species concepts under
the title “On the failure of modern species concepts.”
In their comprehensive treatise of speciation Coyne and Orr (2004) basically
adopted Mayr’s biological species concept, because the problem of speciation is
“the origin of discrete groups of organisms living together in nature. […] It seems
undeniable that nearly all recent progress on speciation has resulted from adopting
some version of the biological species concept” (pp. 6–7).The conceptual reasoning
as to species limits in molecular population studies is also based on the biological
species concept.
While a student in Berlin under Erwin Stresemann, Ernst Mayr had become
a representative of the Seebohm-Hartert “school” of European systematic ornithology
which had originated in the late 19th century and, during the course of 100
years, widely influenced ornithology through the work of several well-known
scientists: Seebohm-Hartert-Hellmayr-Stresemann-Rensch, and later Ernst Mayr
himself (Fig. 5.2). The views of these ornithologists as well as those of E.B. Poulton,
K. Jordan, and Ludwig Plate on biological species, subspecies and speciation
7 This was the species concept of numerous 19th century biologists prior to Darwin (1859)
regardless whether they believed in the origin of species through divine intervention
(i.e., creation) or through autochthonous (spontaneous) generation from organic matter
during periods of special environmental conditions. The views of Linnaeus himself and
of several other early naturalists on species were less essentialistic than often stated
(Mayr 1982d: 259; Winsor 2006).