Page:Territory in Bird Life by Henry Eliot Howard (London, John Murray edition).djvu/57

Rh be safely accomplished, and it, too, arrives in that place in advance of the female. With these facts at our disposal, we will endeavour to find an explanation. It is unlikely that specialised behaviour would occur in generation after generation under such widely divergent conditions, and, moreover, expose the birds to risk of special dangers, if it were but an hereditary peculiarity to which no meaning could be attached. Hence the appearance of the males in their breeding haunts ahead of the females becomes a fact of some importance, and suggests that the extensive journey in the one case, and the short journey in the other, may both have a similar biological end to serve.

Darwin evidently attached importance to this difference between the males and the females in their times, of arrival. In the Descent of Man he referred to it as follows: "Those males which annually first migrated in any country, or which in spring were first ready to breed, or were the most eager, would leave the largest number of offspring; and these would tend to inherit similar instincts and constitutions. It must be borne in mind that it would have been impossible to change very materially the time of sexual maturity in the females without at the same time interfering with the period of the production of the young—a period which must be determined by the season of the year." Newton suggested the following explanation : "It is not difficult to