300 The Natural History of Selborne 



pairs, allowance being made for accidents, breed yearly eight pairs 

 more, what becomes annually of this increase ; and what determines 

 every spring which pairs shall visit us, and reoccupy their ancient 

 haunts ? 



Ever since I have attended to the subject of ornithology, I have 

 always supposed that that sudden reverse of affection, that strange 

 avTHTTopyri, which immediately succeeds in the feathered kind to the 

 most passionate fondness, is the occasion of an equal dispersion of 

 birds over the face of the earth. Without this provision one 

 favourite district would be crowded with inhabitants, while others 

 would be destitute and forsaken. But the parent birds seem to 

 maintain a jealous superiority, and to oblige the young to seek for 

 new abodes ; and the rivalry of the males in many kinds, prevents 

 their crowding the one on the other. Whether the swallows and 

 house-martins return in the same exact number annually is not easy 

 to say, for reasons given above ; but it is apparent, as I have 

 remarked before in my Monographies, that the numbers returning 

 bear no manner of proportion to the numbers retiring. 1 



1 Here we get an early hint of that profound problem of multiplication 

 which gave rise later to Malthus's Theory of Population and also to the doctrine 

 of the Struggle for Existence, with its Darwinian and Spencerian corollaries of 

 Natural Selection and the Survival of the Fittest. It is interesting to observe such 

 first tentative advances, as showing the inevitable trend of thought towards ideas as 

 yet unborn. ED. 



