ON VARIATIONS. 



351 



slightly shorter, though one cannot speak with any cer- 

 tainty. The habits of the mice had changed in addi- 

 tion, as they were found to burrow their own holes, no 

 holes burrowed by other animals being available, as in 

 the case of the typical wild mouse. 



The development of the protective colouration and 

 habits probably owes its origin to the short-eared owls 

 and hawks which were noticed to frequent the sand- 

 hills, and which would more readily perceive and cap- 

 ture the darker mice. These would gradually be 

 weeded out, therefore, whilst the light-coloured indi- 

 viduals would survive and propagate their more favour- 

 able characteristics. 



Perhaps the most interesting point of all about these 

 observations is that it has been found possible to fix a 

 time limit for the duration of the evolutionary process. 

 The sandbanks are known to be gradually increasing in 

 area, and, by a careful study of old maps, Jameson 

 found that previous to 1780 they did not exist at all. 

 In 1810 the island was only a quarter of a mile long, 

 so we may conclude that the pale race of mice has had 

 not more than about a hundred years for its evolution. 



Are Acquired Characters Inherited? We see that 



