Yet it has been shown, I think, that this mode of coloration is almost equally important, since it not only aids in the preservation of existing species and in the perpetuation of pure races, but was, perhaps, in its earlier stages, a not unimportant factor in their development.

To it we owe most of the variety and much of the beauty in the colours of animals; it has caused at once bilateral symmetry and general permanence of type; and its range of action has been perhaps equally extensive with that of coloration for concealment.
_Influence of Locality or of Climate on Colour._ Certain relations between locality and coloration have long been noticed.

Mr.Gould observed that birds from inland or continental localities were more brightly coloured than those living near the sea-coast or on islands, and he supposed that the more brilliant atmosphere of the inland stations was the explanation of the phenomenon.[90] Many American naturalists have observed similar facts, and they assert that the intensity of the colours of birds and mammals increases from north to south, and also with the increase of humidity.
This change is imputed by Mr.J.A.Allen to the direct action of the environment.

He says: "In respect to the correlation of intensity of colour in animals with the degree of humidity, it would perhaps be more in accordance with cause and effect to express the law of correlation as a _decrease_ of intensity of colour with a _decrease_ of humidity, the paleness evidently resulting from exposure and the blanching effect of intense sunlight, and a dry, often intensely heated atmosphere.

With the decrease of the aqueous precipitation the forest growth and the protection afforded by arborescent vegetation gradually also decreases, as of course does also the protection afforded by clouds, the excessively humid regions being also regions of extreme cloudiness, while the dry regions are comparatively cloudless districts."[91] Almost identical changes occur in birds, and are imputed by Mr.Allen to similar causes.
It will be seen that Mr.Gould and Mr.Allen impute opposite effects to the same cause, brilliancy or intensity of colour being due to a brilliant atmosphere according to the former, while paleness of colour is imputed by the latter to a too brilliant sun.