some constitutional peculiarities in these beings not
suited to their new condition; though not necessarily causing an ill
state of health. Ought we then to wonder much that those hybrids which
have been produced by the crossing of species with different
constitutional tendencies (which tendencies we know to be eminently
inheritable) should be sterile: it does not seem improbable that the
cross from an alpine and lowland plant should have its constitutional
powers deranged, in nearly the same manner as when the parent alpine
plant is brought into a lowland district. Analogy, however, is a
deceitful guide, and it would be rash to affirm, although it may appear
probable, that the sterility of hybrids is due to the constitutional
peculiarities of one parent being disturbed by being blended with those
of the other parent in exactly the same manner as it is caused in some
organic beings when placed by man out of their natural conditions{255}.
Although this would be rash, it would, I think, be still rasher, seeing
that sterility is no more incidental to _all_ cross-bred productions
than it is to all organic beings when captured by man, to assert that
the sterility of certain hybrids proved a distinct creation of their
parents.

{248} <Note in original.> Animals seem more often made sterile by
being taken out of their native condition than plants, and so are
more sterile when crossed.

We have one broad fact that sterility in hybrids is not closely
related to external difference, and these are what man alone gets
by selection.

{249} See _Var. under Dom._, Ed. ii. vol. II. p. 132; for the case
of the cheetah see _loc cit._ p. 133.

{250} _Var. under Dom._, Ed. ii. vol. II. p. 148.

{251} Quoted in the _Origin_, Ed. i. p. 9.

{252} See _Var. under Dom._, Ed. ii. vol. II. p. 147.

{253} _Var. under Dom._, Ed. ii. vol. II. p. 89.

{254} See _Var. under Dom._, Ed. ii. vol. II. p. 147.

{255} _Origin_, Ed. i. p. 267, vi. p. 392. This is the principle
experimentally investigated in the author's _Cross-and
Self-Fertilisation_.

But it may be objected{256} (however little the sterility of certain
hybrids is connected with the distinct creations of species), how comes
it, if species are only races produced by natural selection, that when
crossed they so frequently produce sterile offspring, whereas in the
offspring of those races confessedly pr