io8 BIOMETRY 



very little effect. If selection is stopped after one 

 generation, and the selected stock is then inbred, it 

 was calculated that the first generation of inbred stock 

 would show 0-59 h, the second 0*56 h, the third 0-52 h, 

 and the tenth 0-35 h. If, on the other hand, in- 

 breeding was started after the selection had continued 

 for a large number of generations, the first generation 

 of inbred stock will show 0-86 h, the second 0-81 h, 

 the third 077 h, and the tenth 0-51 h. So that in- 

 breeding of a selected stock is followed by a very 

 gradual return towards the mean character of the 

 original race.* 



It must be remembered that in the calculation which 

 led to this result perfect normal variability was assumed, 

 and the contribution of every ancestor of the same 

 degree to the hereditary endowment of the offspring 

 was supposed to be exactly equal. Since both these 

 assumptions are very unlikely to be realized in any 

 actual case, the statement here given must only be 

 regarded as an approximate indication of what is 

 likely to take place. 



Some remarkable observations have recently been 

 published by Professor Johannsen, of Copenhagen, and 

 from them are drawn conclusions which seem likely to 

 lead to a distinct advance in our understanding of 

 the process of so-called continuous variation, and of 

 the way in which such variations are transmitted. 



* From this it seems necessarily to follow that it is impos- 

 sible to establish a permanent breed simply by a process of 

 selection. 



