Chap. VII.] THEORY OF NATURAL SELECTION. 309 



that this ^svill have occurred only with plants which had 

 already acquired the power of revolving, and had thus 

 become twiners. 



I have already endeavoured to explain how plants 

 became twiners, namely, by the increase of a tendency 

 to slight and irregular* revolving: movements, which were 

 at first of no use to them ; this movement, as well as that 

 due to a touch or shake, being the incidental result of 

 the power of moving, gained for other and beneficial 

 purposes. Whether, during the gradual development of 

 climbing plants, natural selection has been aided by the 

 inherited effects of use, I will not pretend to decide ; but 

 we know that certain periodical movements, for instance 

 the so-called sleep of plants, are governed by habit. 



I have now considered enough, perhaps more than 

 enough, of the cases, selected with care by a skilful 

 naturalist, to prove that natural selection is incompetent 

 to account for the incipient stages of useful structures ; 

 and I have shown, as I hope, that there is no great diffi- 

 culty on this head. A good opportunity has thus been 

 afforded for enlarging a little on gradations of structure, 

 often associated with changed functions, — an important 

 subject, wliich was not treated at sufficient length in 

 the former editions of this work. I will now briefly 

 recapitulate the foregoing cases. 



AVith the giraffe, the continued preservation of the 

 individuals of some extinct high-reaching ruminant, 

 which had the longest necks, legs, &c, and could browse 

 a little above the average height, and the continued de- 

 struction of those which could not browse so high, would 

 have sufficed for the production of this remarkable quad- 

 ruped ; but the prolonged use of all the parts together 



