Darwin and the Darwinians 155
... repugnance generally to marriage before domestication, ... marriage never prob-
ably excepting from strict domestication, offspring not fertile or at least most
rarely and perhaps never fertile.—No offspring: physical impossibility to marriage.
[ B12 0]
Instinctive feelings against other species for sexual ends... [B161]
There is in nature a real repulsion amounting to impossibility holds good in plants
between all different forms... [B189]
The dislike of two species to each other is evidently an instinct; & this prevents
breeding. [B197]
The existence of wild close species of plants shows there is tendency to prevent the
crossing of animals where there is much facility in crossing there comes the impedi-
ment of instinct [E143f]Kottler observes that at this stage, Darwin agreed with Lyell that intercross-
ing was forced in domestication, and he made non-interbreeding a test of being a
species:
... now domestication depends on perversion of instincts ... & therefore the one dis-
tinction of species would fail [B197]
Definition of species: one that remains at large with constant characters, together
with beings of very near structure [B213]
My definition of species has nothing to do with hybridity, is simply, an instinctive
impulse to keep separate, which no doubt be overcome, but until it is these animals are
distinct species [C161]
A species as soon as once formed..., repugnance to intermarriage—settles it [B24]
Species formed... keep distinct, two species made; ... [B82]Clearly, Darwin is more concerned with the behavior of organisms in natural con-
ditions, not with the mere possibility of intercrossing. A species is to him at this stage
an interbreeding group that is kept separate from other groups not only by the impos-
sibility of hybridization, but also by the mating behaviors of each group. Hence, it
is not a notion that can be lab-tested, although Buffon had famously, and with some
success, tested his idea that Linnaean-level species were geographical variants of the
premiere souche, or primary stock (see above). It has to be observed in the field. But
there were ways to test species:
It is daily happening, that naturalists describe animals as species... There is only two
ways [sic] of proving to them it is not; one where they can [be] proved descendant
[Kottler interpolates: descent from common parents], which of course most rare, or
when placed together they will breed. [B122]The standard view of species at the time, since the original definition by Linnaeus,
was that any two organisms were of the same species if they shared ancestry (in
Linnaeus’ pious formulation, from the pair of creatures created by God). Species are
real, according to Darwin here, when they do not interbreed:
As species is real thing with respect to contemporaries—fertility must settle it [C152]
If they [systematists—JSW] give up infertility in largest sense as test of species—
they must deny species which is absurd. [E24].