with
respect to climate would clearly be an advantage to our plant; but we
have reason to believe that only a few plants or animals range so far,
that they are destroyed by the rigour of the climate alone. Not until
we reach the extreme confines of life, in the arctic regions or on the
borders of an utter desert, will competition cease. The land may be
extremely cold or dry, yet there will be competition between some few
species, or between the individuals of the same species, for the warmest
or dampest spots.

Hence, also, we can see that when a plant or animal is placed in a new
country amongst new competitors, though the climate may be exactly
the same as in its former home, yet the conditions of its life will
generally be changed in an essential manner. If we wished to increase
its average numbers in its new home, we should have to modify it in a
different way to what we should have done 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 our imagination to give any form some
advantage over another. Probably in no single instance should we know
what to do, so as to succeed. It will convince us of our ignorance on
the mutual relations of all organic beings; a conviction as necessary,
as it seems to be difficult to acquire. All that we can do, is to keep
steadily in mind that each organic being is striving to increase at 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.

4.

NATURAL SELECTION.

Natural Selection: its power compared with man's selection, its power
on characters of trifling importance, its power at all ages and on
both sexes. Sexual Selection. On the generality of intercrosses
between individuals of the same species. Circumstances favourable and
unfavourable to Natural Selection, namely, intercrossing, isolation,
number of individuals. Slow action. Extinction caused by Natural
Selection. Divergence of Character, related to the diversity of
inhabitants of any small area, and to naturalisation. Action of Natural
Selection