N0.5G2] THE PROBLEM OF INBREEDING 611 



clearly enough that practictdlt) they make inbreeding syn- 

 onymous with self-fertilization. But here it is not so 

 clear. The discussion in the first two paragraphs on p. 41 

 of the paper seem to me to indicate that in animals Kast 

 and Hayes would make homozygosity the criterion of 

 inbreeding. Thus they say : 



done there are two things to consider, the closeness of niatings and their 

 result. The statement is often made that self-fertilization in plants is a 



With a -enn-to-ge^ tra^ doubtful 

 if this is true. Thus it is perfectly clear that it is not' kinship of the 

 organisms furnishing the sex cells that determines the closeness of the 

 mating, but the similarity of the constitution of the cells themselves. ^ 



vestigations such as studies of cousin marriages in the human race 



But surely to make homozygosity, either of mated indi- 

 viduals or of progeny, a criterion of inbreeding is an un- 

 tenable position. It is the easiest of matters to do either 

 of the following things : 



(a) To produce homozygous offspring from the mating 

 of heterozygous parents (one half of all the offspring of 

 such parents will be homozygous). 



(b) To produce heterozygous offspring from the con- 

 tinued mating of brother X sister. 



(c) To produce homozygous offspring in any numbers, 

 indeed to found and perpetuate a strain purely homo- 

 zygous with reference to any desired character or char- 

 acters, without ever mating together even distantly 

 related individuals, not to mention brother and sister. 



If all of these things are possible, as they certainly are, 

 what becomes of any attempt to make homozygosity a 

 criterion of inbreeding? All effects hitherto attributed 

 to inbreeding may conceivably be due to homozygosity. 

 I am sure, however, that even East and Hayes themselves 

 would not contend that this had been proven experi- 

 mentally for animals. But even granting this to be so it 



