34 DARWINISM AND THE PROBLEMS OF LIFE 



increase already existing characteristics. Just as 

 artificial selection can produce white pigeons from birds 

 of a grey-blue colour, by choosing in each generation 

 the specimens with the largest number of white spots 

 in their plumage, so natural selection can endow animals 

 with entirely new features. Thus, for instance, our 

 hare is not easy to distinguish from the ground on which 

 it browses because of its grey colour — which is a mix- 

 ture of brown, yellow, white, and black.^ Now let us 

 suppose that a glacial period came over England again, 

 as has happened twice in the history of the earth. The 

 dark-coloured hares would then easily meet the eyes of 

 their enemies on the white snow, but there would be 

 varieties with a rather stronger mixture of white in 

 their colouring. These would be least easily seen, 

 would survive the longest, and bring most young into 

 the world ; so that the next generation would in itself be 

 of a lighter shade. Amongst these, again, the lightest 

 would survive best, and this would be repeated in each 

 generation until a pure white coat was produced, as is 

 found in the Arctic hare. We must not forget, of 

 course, that such a modification of colour could only 

 take place if the cold set in gradually, and implied 

 above all the coming of longer and more snowy winters. 

 Natural selection is powerless in face of sudden changes, 

 as it can only modify things gradually. Further, 

 selection only acts generally ; every animal does not 

 survive that is modified in the desired direction. But 

 that the modification can, generally speaking, advance 



* As mentioned in Weismann's " The Evolution Theory." [English 

 Translation.] 



