Artificial and Natural Selection 805 



This change was not permanent, but was ob- 

 served to diminish rapidly and to disappear 

 entirely, whenever the Norwegian strain was 

 cultivated in the southern part of Germany. It 

 was a typical improved race, dependent on con- 

 tinual selection by the short summers which had 

 produced it. Similar results have been reached 

 by Von Wettstein in the comparison of kinds 

 of flax from different countries. The analogy 

 between such cultivated local races and the lo- 

 cal races of nature is quite striking. The prac- 

 tice of seed-exchange rests for a large part on 

 the experience that the characters, acquired un- 

 der the definite climatic and cultural conditions 

 of some select regions, hold good for one or two, 

 and sometimes even more generations, before 

 they decrease to practical uselessness. The 

 Probstei, the Hanna and other districts owe 

 their wealth to this temporary superiority of 

 their wheat and other cereals. 



Leaving these intermediate forms of selec- 

 tion, we now come to our principal point. It 

 has already been discussed at some length in the 

 previous lecture, but needs further consider- 

 ation. It is the question whether intra-specific 

 selection may be regarded as a cause of last- 

 ing and ever-increasing improvement. This 

 is assumed by biologists who consider fluc- 

 tuating variability as the main source of pro- 



