range peculiar to itself.[A]

[G] The distinctions which Naegeli here erects are, of course,
purely arbitrary, and his definitions are suitable for use only
in his own thesis.--_Trans._

18. SOCIAL AND INDIVIDUAL ORIGIN OF SPECIES.

The species arises neither from the _nutrition variety_ nor from the
_race_; it is always a more advanced variety, and hence species
formation is identical with variety formation. Cause for variation and
consequently for variety formation is always shown, either when,
environment remaining the same, the automatic variation of the idioplasm
has advanced so far that the ontogeny is raised to a higher grade of
organization and division of labor, or when external stimuli act for a
sufficiently long time in a manner not in harmony with the previous
adaptation. Hence various varieties arise easily from a uniform kinship,
when these are thrown among unlike external influences by local
separation, because in the separated places on the one hand the
automatic evolution proceeds with unequal rapidity, and on the other
hand adaptation takes place unequally.

But in general different varieties arise socially from a uniform
kinship. This is because the related individuals living together are
unequally stimulated on account of the great inequality of external
influences which may exist at the smallest distances; and also because
with slight individual differences unlike reactions often follow upon
the same external influences. If identically similar individuals are
equally inclined to very different reactions toward the same stimulus,
sometimes the direction of the first variation decides the character of
the adaptation and therefore the nature of the variety, because the
variation, when once begun, progresses unswervingly even under somewhat
different circumstances.[H] Hence divergent variations are found growing
together in all places, which variations have begun at different though
neighboring points by transformation of the idioplasm and are soon
intermingled on account of the easy dissemination of seed.

[H] It is interesting to compare this statement with Weismann's
recent theory of Germinal Selection.--_Trans._

The social formation of varieties is not in general interrupted by
crossing, a process which governs only the formation of races. It is
confirmed according to experience by the universally recurring fact that
several beginnings of the most closely related varieti