Species

196 Species

Karl Jordan’s papers^30 seem to have had some impact on the way people discussed
variation within species, and it contains the core of the biospecies concept later pro-
pounded by Mayr, who mentions Jordan as a “forerunner,”^31 and quotes Jordan’s
statement

Individuals connected by blood relationship form a single faunistic unit in an area ...

the units, of which the fauna of an area is composed, are separated from each other by

gaps which at this point are not bridged by anything.^32

Jordan gave the criteria that he believed dened two organisms as being in the
same or different species in the context of a discussion of the variation of physical
traits in organisms that we use to establish the “blood relationships of individuals
and thus the physical gaps between species.”^33 He said that individuals of two species
announce themselves by having physiological differences that they always reproduce
in their progeny, and by being able to live in the same region without blending into
each other. He listed three criteria:

The criteria of the species [he uses the Latin word “species” here—JSW] (= Art)

concept are thus threefold, and each individual point is an applicable test: a species

requires known traits, it does not beget descendants equally well with individuals of

other species, and it does not coalesce into other species.^34

Jordan’s view seems to require not only geographical isolation, but also constancy

of characters, which Mayr’s later denition does not. He goes on to say that the

non-coalescence (non-hybridization) of species explains the “enormous number” of

extant species, and that this is due to the internal organization of the species (by

which I take him to mean of the typical genetic structure of the species). He makes

the comment that species act as if there were “no relationship between them, but as

if they were doing business for themselves.”^35

(^30) Especially Jordan 1905.
(^31) Mayr 1982, 285.
(^32) Jordan 1905, 157:
(^) Solche blutsverwandte Individuen bilden eine faunistische Einheit in einem Gebeit ...
which Jordan follows with the elided comment
(^) zu welcher Einheit wir erfährungsgemäß alle andern Individuen des Gebeits rechnen müssen,
welche ihnen gleichen
meaning roughly that we assign all individuals to these units when we empirically classify them as
identical. Again, there is an epistemological element here that is overlooked. The subsequent state-
ment Mayr quotes comes after a number of examples of this classication.
(^33) Jordan 1905, 159.
(^34) Thanks to Ian Musgrave for help with the translation:
(^) Das Kriterium des Begriffs Species (=Art) ist daher ein dreifaches, und jeder einzelne Punkt ist
der Prüfung zugänglich: Eine Art bat gewisse Körpermerkmale, erzeugt keine den Individuen
anderer Arten gleich Nachkommen und verschmilzt nicht mit andern Arten.
(^35) Op. cit., 160: “... als ob nie ein Zusammenhang zwischen ihnen gewesen, als ob jede Art für sich
geschaffen ware.” Italics represent emphatic spacing.