certain limits, and which, in all likelihood, is by no means exclusively
exerted by our species.[233] The growth of human population cannot take
place without diminishing the numbers, or causing the entire
destruction, of many animals. The larger beasts of prey, in particular,
give way before us; but other quadrupeds of smaller size, and
innumerable birds, insects, and plants, which are inimical to our
interests, increase in spite of us, some attacking our food, others our
raiment and persons, and others interfering with our agricultural and
horticultural labors. We behold the rich harvest which we have raised by
the sweat of our brow, devoured by myriads of insects, and are often as
incapable of arresting their depredations, as of staying the shock of an
earthquake, or the course of a stream of lava.

A great philosopher has observed, that we can command nature only by
obeying her laws; and this principle is true even in regard to the
astonishing changes which are superinduced in the qualities of certain
animals and plants by domestication and garden culture. I shall point
out in the third book that we can only effect such surprising
alterations by assisting the development of certain instincts, or by
availing ourselves of that mysterious law of their organization, by
which individual peculiarities are transmissible from one generation to
another.[234]

It is probable from these and many other considerations, that as we
enlarge our knowledge of the system, we shall become more and more
convinced, that the alterations caused by the interference of man
deviate far less from the analogy of those effected by other animals
than is usually supposed.[235] We are often misled, when we institute
such comparisons, by our knowledge of the wide distinction between the
instincts of animals and the reasoning power of man; and we are apt
hastily to infer, that the effects of a rational and irrational species,
considered merely as _physical agents_, will differ almost as much as
the faculties by which their actions are directed.

It is not, however, intended that a real departure from the antecedent
course of physical events cannot be traced in the introduction of man.
If that latitude of action which enables the brutes to accommodate
themselves in some measure to accidental circumstances could be imagined
to have been at any former period so great, that the operations of
instinct were as much diversified as are those of human reas