124 



THE AMERICAN NATURALIST 



[VOL.LV 



Many of the older writers on heredity have held that 

 inbreeding is a cause of degeneration. In avoiding am- 

 biguous words ' ' cause ' ' is one of the first that must go. If 

 forced to define their position this school would probably 

 be content with the statement that degeneration is a nec- 

 essary consequence of inbreeding, the intermediate steps 

 or nature of the process being unknown. Is this concep- 

 tion really at variance with the idea that degeneration 

 results from the increased number of unfavorable re- 

 cessive characters brought into expression by increasing 

 homozygosity? Does not this conception rather amplify 

 the older, general and indefinite position by explaining 

 how the degeneration may be brought about? 



It excites unnecessary opposition, and is not entirely 

 fair, to read into the early writings the idea that inbreed- 

 ing was held to be the immediate and direct cause of the 

 subsequent degeneration. Such words as "cause" and 

 "per se" have perhaps been used, but is there not suflB- 

 cient latitude in their meaning to allow the later dis- 

 coveries to be looked upon as explaining rather than re- 

 futing the old doctrine ? 



In the attempt to bring the two views into sharp con- 

 trast the newer explanation is sometimes stated in terms 

 which likewise must be interpreted with latitude if the 

 explanation is to be accepted. Thus East and Jones (p. 

 123) state one of the results of inbreeding maize as fol- 

 lows: "There is a reduction in size of plant and produc- 

 tiveness which continues only to a certain point and is in 

 no sense an actual degeneration." It is difficult to 

 imagine a degeneration more "actual" than that usually 

 following the inbreeding of maize. 



In another place (p. 139) the same authors say: "The 

 only injury proceeding from inbreeding comes from the 

 inheritance received." Such statements have an unfor- 

 tunate air of finality that probably was not intended. 

 The relation between inbreeding and degeneration has 

 been greatly clarified by the work of these authors, but 

 the above statement taken literally places them in a posi- 



