190 INBREEDING AND OUTBKEEDING 



any clear-cut segregation. Yet reduction in fertility is 

 noticeable only so long as there is a change in other char- 

 acters, constancy in visible characters being accompanied 

 by a constancy in the matter of fertility. In other words, 

 there is no more an accumulation of sterility on con- 

 tinued inbreeding than there is an accumulation of any 

 other effect. Any reduction in fertility ceases when 

 homozygosity is reached, but the end result may be 

 decidedly different in various lines coming originally from 

 the same stock. 



Many other instances of an effect of inbreeding upon 

 fertility might be given, particularly the appearance of 

 abnormalities in the genital organs, both external and in- 

 ternal. But what we desire is to show their meaning 

 rather than to catalogue them, and for this purpose no 

 data have been gathered as valuable as those upon the 

 much cited maize. Examination of all the isolated facts 

 brought to light in both animals and plants shows such a 

 similar trend that there is no reason to believe we are not 

 dealing with manifestations of one and the same law, yet 

 only in this species do we have a critical test of the hypoth- 

 eses involved. And here it can be stated unequivocally 

 and without reservation that the effect of inbreeding on 

 fertility is exactly the same as its effect upon other char- 

 acters. Recessive combinations deleterious to the func- 

 tion of reproduction are brought to light. But this is not 

 the only conclusion to be drawn. The frequency with 

 which depression of fertility occurs during inbreeding, the 

 slowness with which it is brought to an end, the variety 

 of differences which is brought out, all show how complex 

 one must conclude the function of reproduction to be, and 

 how many variations affecting it must be constantly occur- 



