Page:The British Warblers A History with Problems of Their Lives - 9 of 9.djvu/54

 put forward that climate may exercise some influence upon the vocal muscles irrespective of natural selection, and thereby contribute towards the differences we discern. The problem is a difficult one and recent observation adds to the complexity. One wants to know whether it is an isolated phenomenon, removed from the general course of evolution, or whether it is linked with other physiological differences which we cannot yet fully determine, though we are beginning perhaps to understand them in part. As our knowledge of local races increases, so the importance of this vocal variation looms large in our field of inquiry. We cannot altogether disregard it. For even if it could be shown that varying climates could exercise differential effects on the vocal muscles, there would still remain plenty of matter for debate. Is there such a thing in song as a definite ancestral type? And if not, at what period in the life of the individual is the voice fashioned? This is the crux of the whole matter. I have suggested climate and I still hold to it as a directing influence, because, if we regard the facts presented as a whole, we find one feature which arrests our attention and may almost be spoken of as universal, namely, an alteration of the pitch in different districts; the farther we travel west—I am speaking of Europe—the more we observe the phenomena in districts dominated by the Atlantic, the lower we find the pitch becomes. If every individual of the same species and in the same locality presented this peculiarity in a similar degree, the matter would be more simple. But this is not the case. Two Chaffinches will utter their spring call side by side in Donegal, both in a lower pitch than one is accustomed to hear in the Midland counties of England, but the one so very much lower as to make the possibility of recognition by other members of the same species in other localities somewhat remote. With the meagre facts at our disposal it would be unwise to attempt to arrive at any decision. The phenomenon is probably part of the larger problem of local races, but whether the delicate adjustments which these slight differences imply are due