improved races of domesticated plants and animals:

"One need not be a pessimist to assert the actual evidence thus far
obtained indicates that the supposed progress made in the improvement of
domesticated animals and plants is nothing more than the sorting out of
pure lines, and thus represents no advancement."--Prof. L.B. Walton,
_Science_, April 3, 1914.]

Nor is there any other method known to modern science by means of which
new factors can be originated which were not potentially latent in the
ancestry. The much heralded new "species" of de Vries and others are now
known to be merely new factors cropping out;[31] for though they remain
constant and breed true, they obey Mendel's Law when crossed with their
parental forms, and hence are merely the result of some new combination
of factors which can be reproduced at will by using the same method of
combination and segregation. The real scientific test for any form
supposed to be a new "species" would be twofold: (1) to show that some
new character had been added which no ancestor ever possessed; and (2)
to show that this new character will breed true under all circumstances
of hybridization and not merely segregate as a unit character or mere
analytic variety after hybridization. It is almost superfluous to say
that no "new species" originating in modern times has ever justified
itself under these tests.

[Footnote 31: Some of our leading biologists are now disposed to grow
somewhat humorous when speaking of this mutation theory of de Vries, as
may be illustrated by the following:

"The mutation theory of de Vries appears accordingly to lag useless on
the biological stage, and may apparently be now relegated to the limbo