T'he Natural History of Selborne 313 



rest build in some of the lowest and meanest thatched cottages. 

 Now as these eight 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 avriaropyr), 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 superi- 

 ority, 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 num- 

 bers 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. 



