erent way
to what we should have had to do in its native country; for we should
have to give it some advantage over a different set of competitors or
enemies.

It is good thus to try in imagination to give to any one species an
advantage over another. Probably in no single instance should we know
what to do. This ought to convince us of our ignorance on the mutual
relations of all organic beings, a conviction as necessary as it is
difficult to acquire. All that we can do is to keep steadily in mind
that each organic being is striving to increase in a geometrical ratio;
that each at some period of its life, during some season of the year,
during each generation or at intervals, has to struggle for life and to
suffer great destruction. When we reflect on this struggle, we may
console ourselves with the full belief that the war of nature is not
incessant, that no fear is felt, that death is generally prompt, and
that the vigorous, the healthy, and the happy survive and multiply.

3. Competition, Specialization, and Organization[186]

Natural selection acts exclusively by the preservation and accumulation
of variations, which are beneficial under the organic and inorganic
conditions to which each creature is exposed at all periods of life. The
ultimate result is that each creature tends to become more and more
improved in relation to its conditions. This improvement inevitably
leads to the gradual advancement of the organization of the greater
number of living beings throughout the world.

But here we enter on a very intricate subject, for naturalists have not
defined to each other's satisfaction what is meant by an advance in
organization. Amongst the vertebrata the degree of intellect and an
approach in structure to man clearly come into play. It might be thought
that the amount of change which the various parts and organs pass
through in their development from the embryo to maturity would suffice
as a standard of comparison; but there are cases, as with certain
parasitic crustaceans, in which several parts of the structure become
less perfect, so that the mature animal cannot be called higher than its
larva. Von Baer's standard seems the most widely applicable and the
best, namely, the amount of differentiation of the parts of the same
organic being, in the adult state, as I should be inclined to add, and
their specialization for different functions; or, as Milne Edwards would
express it, the completeness of the di