Mr. Gould believes that birds of
the same species are more brightly coloured under a clear atmosphere, than
when living near the coast or on islands; and Wollaston is convinced that
residence near the sea affects the colours of insects. 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. These slightly varying
organisms are interesting in as far as they present characters analogous to
those possessed by the species which are confined to similar conditions.
When a variation is of the slightest use to any being, we cannot tell how
much to attribute to the accumulative action of natural selection, and how
much to the definite action of the conditions of life. Thus, it is well
known to furriers that animals of the same species have thicker and better
fur the further north they live; but who can tell how much of this
difference may be due to the warmest-clad individuals having been favoured
and preserved during many generations, and how much to the action of the
severe climate? For it would appear that climate has some direct action on
the hair of our domestic quadrupeds.
Instances could be given of similar varieties being produced from the same
species under external conditions of life as different as can well be
conceived; and, on the other hand, of dissimilar varieties being produced
under apparently the same external conditions.
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