236 Animal Life and Intelligence. 



advantage. Among thousands of independent variations 

 in the lengths of the bones there would be occasional com- 

 binations of variations, giving either increased length or 

 increased breadth to the wing. In the noctule, the former 

 would tend to be selected; in the horse-shoe, the latter. 

 Thus the wing of the noctule would be lengthened, and that 

 of the horse-shoe broadened, through the selection of for- 

 tuitous combinations of variations which chanced to be 

 favourable. Now, each individual bone-variation is, we 

 believe, due to some special cause ; but the fortunate com- 

 bination is fortuitous, due to what we term " mere chance." 



Darwin believed that chance, in this sense, played a 

 very important part in the origin of those favourable 

 variations for which, as he said, natural selection is con- 

 stantly and unceasingly on the watch. And there can be 

 little question that Darwin was right. 



We must now consider very briefly some of the proxi- 

 mate causes of variations. In most of these cases we 

 cannot hope to unravel the nexus of causation. When a 

 plexus of environing circumstances acts upon a highly 

 organized living animal, the most we can do in the present 

 state of knowledge is to note — we cannot hope to explain — 

 the effects produced. 



All readers of Darwin's works know well how insistent 

 he was that the nature of the organism is more important 

 than the nature of the environing conditions. " The 

 organization or constitution of the being which is acted 

 on," he says,* "is generally a much more important 

 element than the nature of the changed conditions in 

 determining the nature of the variation." And, again,f 

 " We are thus driven to conclude that in most cases the 

 conditions of life play a subordinate part in causing any 

 particular modification ; like that which a spark plays 

 when a mass of combustible matter bursts into flame — the 



* " Animals and Plants under Domestication," vol. ii. p. 201. 



t Ibid. p. 282. The phenomena of the seasonal dimorphism of butterflies 

 and moths show that changes of temperature (and perhaps moisture, etc.) 

 determine very striking differences in these insects. 



