662 Studies in the Theory of Descent. 



increase to a higher percentage of the total 

 population ; nevertheless their numbers would 

 constantly but very slowly augment. In the 

 course of time this increase would become more 

 rapid for two reasons first, because even a very 

 small advantage in favour of the increasing 

 number of individuals would always leave a 

 greater number of these victorious; and secondly, 

 because on the whole as the climate became more 

 arctic, the advantage of being* white would con- 

 tinually become more decisive in determining 

 which should live and which should succumb. 



Thus I see no reason why individual variations 

 which do not appear only once, but which fre- 

 quently recur in the course of generations, should 

 not acquire predominance under favourable con- 

 ditions. All facts are in accord with this. Even 

 the common hare shows us that it would be quite 

 capable of becoming coloured in a similar manner. 

 In the museum of Stuttgart there are three speci- 

 mens of Lepus timidus, killed in Wurtemburg, 

 which are completely white, and several others 

 which are silver-grey or spotted with white. In 

 eastern Russia the common hare possesses a 

 light grey, almost white, winter coat, and Seid- 

 litz 8 makes known the interesting observation 

 that such light specimens occur singly in Livpnia, 

 where " the common hare has become naturalized 

 since the commencement of the century." 

 8 "Die Darwin'sche Theorie," Dorpat, 1875. 



