OLD TYPES AND NEW 209 



The difference between the unthinkable number 

 given above and the actual number of probable an- 

 cestors alive thirty generations/, : ago emphasizes the 

 fact that inbreeding must have occurred freely. 



Cousin-marriages, although producing a high per- 

 centage of defects, do not necessarily produce unde- 

 sirable traits. They simply bring , out latent or re- 

 cessive characters for the reason that under these con- 

 ditions defect meets defect instead of the opposite 

 normal condition which would dominate the defect and 

 cause it not to appear. 



Since a recessive trait may be properly regarded as 

 the absence of a positive dominant character, it more 

 frequently stands for an undesirable feature than 

 otherwise. Thus it comes about that inbreeding, by 

 combining negative features, may "produce" a defec- 

 tive strain. 



Outcrossing always increases heterozygous combi- 

 nations in the germplasm and covers up undesirable^ 

 recessive traits through the introduction of additional \ 

 dominant traits. Inbreeding, on the contrary, tends ; 

 to simplify the germplasm, that is, to make it more ; 

 homozygous, and so to bring recessive defects to the ; 

 surface. 



D. HYBRIDIZATION y/ 



Among the first to use the powerful tool of hybridi- 

 zation were Koelreuter, 1733-1806, in Germany, and 

 Knight, 1758-1838, in England. These pioneer trans- 

 gressors of the Mosaic law cited in the foregoing para- 

 graph, opened up a broad road to the army of the 

 Mendelians who were to follow them. Not only have 



