No. 586] 



SELECTION OF A CHARACTER 



607 



IV 



What bearing have these results upon the general prob- 

 lem of the effectiveness of selection in modifying ger- 

 minal determiners ! Let us at the outstart endeavor to 

 be quite clear as to the problem. It lias been shown in 

 what has preceded that in the long experiment a change 

 in the average condition of the population has occurred, 

 and has been coincident with selection. The writer has 

 no hesitation in saying that the increase in average pro- 

 ductiveness since 1908 has been caused by the particular 

 kind of selective breeding practised. Furthermore the 

 average productiveness at the present time transcends 

 any average known in the previous history of the stock. 



Granting all this, however, as plain matter of fact, it 

 does not, in the writer's opinion, afford one iota of evi- 

 dence that through the process of selection the hereditary 

 determiners of fecundity either have been or can be 

 changed. All that the selection has done, so far as we 

 have any evidence, is to change the constitution of the 

 population in respect of fecundity genotypes. There is 

 no evidence that the genotypes themselves have been 

 changed. On the contrary, everything indicates that they 

 have not been changed. During the last seventeen years 

 we have merely sorted out from a mixed population, by a 

 systematic method of breeding, those individuals which 

 were alike in one respect, and have sold all the rest to the 

 butcher. That one respect was that each individual bore 

 progeny which were high producers. 10 Those individuals 

 chosen as breeders in 1908 and 1914 were precisely alike 

 in this particular There were more of them available 

 in proportion to the whole flock in 1914 than in 1908, but, 

 as individuals, I am unable to discern any particular in 

 which they were different in 1914 from what they were in 

 1908. 



The general point here involved is essentially the same 

 as one with which we are more familiar in demographic 



