Somatic Variations 



to be born white. In such a case, it is unlikely 

 that the fur of an organism which is naturally 

 coloured will be completely bleached by the 

 snow, and, even if it be, the bleaching process 

 will take time, meanwhile the creature will be 

 comparatively conspicuous. So that those which 

 are naturally whiter than the average, that is to 

 say, those in which the tendency to whiteness 

 appears as a germinal variation, will be less con- 

 spicuous than those which tend to be the ordinary 

 colour. Thus the former will enjoy a better 

 chance of survival, and will be likely to transmit 

 their whiteness to their offspring in so far as it 

 is due to a germinal or congenital variation. 



Thus, although none of the whiteness due to 

 somatic variations is transmitted to the offspring, 

 such variations are of considerable importance 

 to the species, as they enable it to survive and 

 allow time for the germinal variations in the 

 required direction to appear. 



That this case need not be purely hypothetical 

 is shown by the fact that dun domestic pigeons, 

 which are of an earthy-brown colour when fresh 

 moulted, soon fade in the sun to a dull creamy 

 hue. Thus a coloration adapted to an ordinary 

 soil could soon be suited to a desert environ- 

 ment. The ruddy sheldrake also, normally a 

 bright chestnut- coloured bird, and one that haunts 

 exposed sunny places, in many cases fades very 

 much, becoming almost straw-coloured. 



109 



