INHERITANCE OF FECUNDITY 263 



key on the inside, proceeded to attempt to get out by beating 

 and kicking against the door in bhnd fury, rather than take the 

 trouble to find the location of the key and unlock the door. There 

 is just a possibility that he could finally get out in a very few 

 instances by the first method, but even in those cases he would be 

 regarded by sensible men as rather a fool for his pains. 



Of course what has been said is not meant to imply that selec- 

 tion on the basis of somatic conditions may not have a part in a 

 well considered system of breeding for a particular end. In 

 many cases it certainly will have. Thus in the case of fecundity 

 in the fo"^ls, selection of mothers on the basis of fecundity records 

 is essential in getting male birds homozygous with respect to 

 Li and L^. But the point which seems particularly clear in the 

 light of the present results is that blind mass selection, on the 

 basis of somatic characters only is essentially a haphazard system 

 of breeding which may or may not be successful in changing the 

 type in a particular case. There is nothing in the method per se 

 which insures such success, though that there is inherent potency . 

 in the method per se is precisely the burden of a very great pro- 

 portion of the teaching of breeding (in whatever form that teach- 

 ing is done) at the present time. 



It seems to me that it has never been demonstrated, up to 

 the present time, that continued selection can do anything more 

 than: 



1. Isolate pure biotypes from a mixed population, which con- 

 •tains individuals of different hereditary constitution in respect 

 to the character or characters considered. 



2. Bring about, as a part of a logical system of breeding for 

 a particular end, certain combinations of hereditary factors which 

 would never (or very rarely) have occurred in the absence of such 

 systematic selection ; which combinations give rise to somatic types 

 which may be quite different from the original types. In this 

 way a real. evolutionary change (i.e., the formation of a race 

 of qualitatively different hereditary constitution from anything 

 existing before) may be brought about. This can unquestion- 

 ably be done for fecundity in the domestic fowl. But here 'selec- 

 tion' is simply one part of a system of breeding, which to be suc- 

 cessful must be based on a definite knowledge of gametic as well 



