ay be, which
distinguishes natural species of animals. Can we find any approximation
to this in the different races known to be produced by selective
breeding from a common stock? Up to the present time the answer to that
question is absolutely a negative one. As far as we know at present,
there is nothing approximating to this check. In crossing the breeds,
between the fantail and the pouter, the carrier and the tumbler, or any
other variety or race you may name--so far as we know at present--there
is no difficulty in breeding together the mongrels." However, he
continues, as soon as you remove the conditions which produced the new
variety,--as when you permit pigeons to mate promiscuously,--no matter
how different the varieties may have been, you will have, in a few
generations of pigeons, the same blue rock pigeon with the black bars
across the wings. No new species has originated. All varieties, in a
free state, revert to type. "This," says Huxley, "is certainly a very
remarkable circumstance."

Fairhurst points out the difficulties in which the evolutionist becomes
involved through the fixity of species. He writes: "It is well known
that as a rule distinct species will not cross, and that if they do
cross the offspring are not fertile. On the other hand, it is true that
all _varieties_ of a species readily cross, producing fertile offspring.
This has commonly been regarded as a well-defined distinction between
varieties and species. If the varieties of pigeons which are so
different from each other did not freely cross, and if the mongrel
offspring were not fertile, Darwin's argument as to the production of
new _species_ under domestication would be complete. The fact is, we do
not know of the origin of any two species of animals that do not cross
and whose offspring are not fertile; in other words, we do not know of
the origin of _species,_ but only of _varieties_. The origin of species
that will not cross and produce fertile offspring is _assumed_ from the
origin of varieties that do cross and produce fertile offspring. This
leaves the evolutionists to account for one of the most difficult things
in connection with this theory, namely, how did varieties of animals of
the same species become cross-sterile?* [[*So that they were unable to
interbreed. Only if such cross-sterility exists, could they exist
thereafter as independent new species.--G.]] Several things must occur
simultaneously before cross-sterility betw