clear how, as I believe, natural selection acts, I must beg permission
to give one or two imaginary illustrations. Let us take the case of a
wolf, which preys on various animals, securing some by craft, some by
strength, and some by fleetness; and let us suppose that the fleetest
prey, a deer for instance, had from any change in the country increased
in numbers, or that other prey had decreased in numbers, during that
season of the year when the wolf is hardest pressed for food. I can
under such circumstances see no reason to doubt that the swiftest and
slimmest wolves would have the best chance of surviving, and so be
preserved or selected, provided always that they retained strength to
master their prey at this or at some other period of the year, when
they might be compelled to prey on other animals. I can see no more
reason to doubt this, than that man can improve the fleetness of his
greyhounds by careful and methodical selection, or by that unconscious
selection which results from each man trying
to keep the best dogs without any thought of modifying the breed.
Even without any change in the proportional numbers of the animals on
which our wolf preyed, a cub might be born with an innate tendency to
pursue certain kinds of prey. Nor can this be thought very improbable;
for we often observe great differences in the natural tendencies of our
domestic animals; one cat, for instance, taking to catch rats, another
mice; one cat, according to Mr. St. John, bringing home winged game,
another hares or rabbits, and another hunting on marshy ground and
almost nightly catching woodcocks or snipes. The tendency to catch rats
rather than mice is known to be inherited. Now, if any slight innate
change of habit or of structure benefited an individual wolf, it would
have the best chance of surviving and of leaving offspring. Some of its
young would probably inherit the same habits or structure, and by the
repetition of this process, a new variety might be formed which would
either supplant or coexist with the parent-form of wolf. Or, again, the
wolves inhabiting a mountainous district, and those frequenting the
lowlands, would naturally be forced to hunt different prey; and from
the continued preservation of the individuals best fitted for the two
sites, two varieties might slowly be formed. These varieties would
cross and blend where they met; but to this subject of intercrossing we
shall soon have to return. I may add, that, according to Mr. Pierce,
there are two varieties of the wolf inhabiting the Catskill Mountains
in the United States, one with a light greyhound-like form, which
pursues deer, and the other more bulky, with shorter legs, which more
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