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, t 

 " 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. 



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

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

 determine very strikiug differences in these insects. 



