Page:The British Warblers A History with Problems of Their Lives - 2 of 9.djvu/48

 menced he would immediately join in, the clicking of all the bills making quite an unusual noise.

These examples show under what diverse conditions the inquisitiveness occurs, and all members of the species appear to be equally susceptible to the same stimulating circumstances. By the use of the term "inquisitiveness" I do not wish to imply an intelligent appreciation on the part of the bird of its various actions; the construction intended to be placed upon it is a figurative one, the purpose being to make clear the type of action when viewed from the human standpoint.

It is so generally accepted that plasticity of instinct has been established as a law of Nature that I almost refrain from questioning the correctness of this view; nevertheless, the more I reflect upon the facts, which I have from time to time collected, the more I feel disposed to regard as doubtful, not so much the possibility of isolated cases of variation arising, though there is little evidence in support of this, but whether the extent to which it has been thought to have been shown that they do occur, is sufficient to justify our accepting such a law as beyond dispute. Owing, perhaps, to the great difficulty of establishing this on the basis of actual observation, it seems to have been assumed too readily that they do occur, but whatever difficulty there may be in this direction can only arise from the rarity or possible absence of true variation, and we ought on this account to be very cautious before arriving at any definite decision.