INHEraTANCE of" FECUNDITY IN DOMESTIC EOWI,. 389 



in the same case as a man who, finding himself imprisoned in a 

 dungeon with a securely locked and very heavy and strong door 

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

 beating and kicking against the door in blind 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 

 man}^ cases it certainly will have. Thus in the case of fecundity 

 in the fowls, selection of mothers on the basis of fecundity re- 

 cords is essential in getting male birds homozygous with respect 

 to Li and Z.2. 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 proportion of the teaching of breeding (in whatever 

 form that teaching 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 

 contains individuals of different hereditary constitution in re- 

 spect 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 woukl never ( or very rarely) have occurred in the ab- 

 sence O'f 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 forma- 

 tion of a race of cjualitatively different hereditary constitution 

 from anything existing before) may be brought about. This 

 can unquestionably be done for fecundity in the domestic fowl. 



