OBNITHOLOGICAL OBSERVATION IN ICELAND. 219 



incubation by the parent bird must be held to be of benefit to 

 the species, we might expect that, from this point, Natural 

 Selection would have brought it about. 



On the above view, the first early acts from which the 

 instincts both of incubation and nidification have been, through 

 Natural Selection, developed, were entirely unintelligent ones, 

 due to the intense state of sexual excitement which birds fall 

 into, every year, on the approach of the breeding-season, and, 

 under the influence of which, they may be actually seen to go 

 through the oddest and most uncouth actions, having no 

 imaginable object, unless the relief of pent-up emotion can be 

 said to be one, and which seem as little the outcome of any 

 process of reason as it is possible for an act to be. This state 

 of overwrought excitement and intense nervous energy of a 

 special kind I have called the sexual frenzy, and if the 

 important main act which arises out of it — coition, namely — 

 may be called an instinct, all those secondary ones which 

 accompany and surround it — rollings, tumblings, springings, 

 prostrations, flutterings, cryings, callings, melodisings, &c, 

 must be pronounced instinctive also. As everybody knows, 

 these storms of desire are either, in themselves, more acute, or, 

 at least, produce a greater crop of strange movements in birds 

 than in any other division of the animal kingdom. Con- 

 sequently, we have, in their case, a larger output of what one 

 may call waste material for Natural Selection, if possible, to put 

 to some use, so that, far from its being extraordinary, we might 

 have expected, if the principle relied on be a true one, that 

 something very special and particular would have been evolved 

 under its action. And Natural Selection, in my opinion, has 

 answered to the call, for out of this maelstrom of blind, formless 

 animal movement, with nothing but sheer concupiscence behind 

 it, she has, on the one hand, evolved the most elaborate, ordered 

 and beautiful forms of sexual display, and, on the other, the 

 still greater and seemingly wholly dissociated marvels of nest- 

 building. This view of the common origin of both these 

 instincts has the merit of simplicity, and moreover it strikes at 

 the root of various objections which are constantly being 

 brought against the theory of one of them only, namely, sexual 

 display, though logically they should be equally valid against 



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