more or less liability to reversion during many subsequent generations, and it
is this fact which has probably led authors to maintain that a score or more
of generations are requisite for one race to absorb another. In considering
the final result of the commingling of two or more breeds, we must not forget
that the act of crossing in itself tends to bring back long-lost characters
not proper to the immediate parent-forms.

With respect to the influence of the conditions of life on any two breeds
which are allowed to cross freely, unless both are indigenous and have long
been accustomed to the country where they live, they will, in all probability,
be unequally affected by the conditions, and this will modify the result. Even
with indigenous breeds, it will rarely or never occur that both are equally
well adapted to the surrounding circumstances; more especially when permitted
to roam freely, and not carefully tended, as is generally the case with breeds
allowed to cross. As a consequence of this, natural selection will to a
certain extent come into action, and the best fitted will survive, and this
will aid in determining the ultimate character of the commingled body.

How long a time it would require before such a crossed body of animals would
assume a uniform character within a limited area, no one can say; that they
would ultimately become uniform from free intercrossing, and from the survival
of the fittest, we may feel assured; but the characters thus acquired would
rarely or never, as may be inferred from the previous considerations, be
exactly intermediate between those of the two parent-breeds. With respect to
the very slight differences by which the individuals of the same sub-variety,
or even of allied varieties, are characterised, it is obvious that free
crossing would soon obliterate such small distinctions. The formation of new
varieties, independently of selection, would also thus be prevented; except
when the same variation continually recurred from the action of some strongly
predisposing cause. We may therefore conclude that free crossing has in all