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, 
109g 
