limate, food, etc., produces on
any being is extremely doubtful. My impression is, that the effect is
extremely small in the case of animals, but perhaps rather more in that
of plants. We may, at least, safely conclude that such influences cannot
have produced the many striking and complex co-adaptations of structure
between one organic being and another, which we see everywhere
throughout nature. Some little influence may be attributed to climate,
food, etc.: thus, E. Forbes speaks confidently that shells at their
southern limit, and when living in shallow water, are more brightly
coloured than those of the same species further north or from greater
depths. Gould believes that birds of the same species are more brightly
coloured under a clear atmosphere, than when living on islands or near
the coast. So with insects, Wollaston is convinced that residence near
the sea affects their colours. Moquin-Tandon gives a list of plants
which when growing near the sea-shore have their leaves in some degree
fleshy, though not elsewhere fleshy. Several other such cases could be
given.

The fact of varieties of one species, when they range into the zone of
habitation of other species, often acquiring in a very slight degree
some of the characters of such species, accords with our view that
species of all kinds are only well-marked and permanent varieties. Thus
the species of shells which are confined to tropical and shallow seas
are generally brighter-coloured than those confined to cold and deeper
seas. The birds which are confined to continents are, according to
Mr. Gould, brighter-coloured than those of islands. The insect-species
confined to sea-coasts, as every collector knows, are often brassy or
lurid. Plants which live exclusively on the sea-side are very apt to
have fleshy leaves. He who believes in the creation of each species,
will have to say that this shell, for instance, was created with bright
colours for a warm sea; but that this other shell became bright-coloured
by variation when it ranged into warmer or shallower waters.

When a variation is of the slightest use to a being, we cannot tell how
much of it to attribute to the accumulative action of natural selection,
and how much to the conditions of life. Thus, it is well known to
furriers that animals of the same species have thicker and better fur
the more severe the climate is under which they have lived; but who
can tell how much of this difference may be due t