ces, extremely slight modifications in
the structure or habits of one species would often give it an advantage
over others; and still further modifications of the same kind would
often still further increase the advantage, as long as the species
continued under the same conditions of life and profited by similar
means of subsistence and defense. No country can be named, in which all
the native inhabitants are now so perfectly adapted to each other and to
the physical conditions under which they live, that none of them could
be still better adapted or improved; for in all countries the natives
have been so far conquered by naturalized productions that they have
allowed some foreigners to take firm possession of the land. And as
foreigners have thus in every country beaten some of the natives, we may
safely conclude that the natives might have been modified with
advantage, so as to have better resisted the intruders.

As man can produce, and certainly has produced, a great result by his
methodical and unconscious means of selection, what may not Natural
Selection effect? Man can act only on external and visible characters;
Nature, if I may be allowed to personify the natural preservation or
survival of the fittest, cares nothing for appearances, except in so far
as they are useful to any being. She can act on every internal organ, on
every shade of constitutional difference, on the whole machinery of
life. Man selects only for his own good; Nature only for that of the
being which she tends. Every selected character is fully exercised by
her, as is implied by the fact of their selection. Man keeps the
natives of many climates in the same country; he seldom exercises each
selected character in some peculiar and fitting manner; he feeds a long
and a short-beaked pigeon on the same food; he does not exercise a
long-backed or long-legged quadruped in any peculiar manner; he exposes
sheep with long and short wool to the same climate. He does not allow
the most vigorous males to struggle for the females. He does not rigidly
destroy all inferior animals, but protects during each varying season,
as far as lies in his power, all his productions. He often begins his
selection by some half-monstrous form; or at least by some modification
prominent enough to catch the eye or to be plainly useful to him. Under
Nature, the slightest differences of structure or constitution may well
turn the nicely balanced scale in the struggle for life,