PRESIDENTIAL ADDRESS. 265 



cLaracter in the individuals born is marl^edly inferior to the 

 mean value of the character in the few individuals which 

 would normally be selected for survival. It might be found 

 that the inferior individuals are for some reason prepotent 

 over superior individuals, so that when an inferior and a 

 superior individual are mated, the offspring inherit the in- 

 feriority to a greater degree than the superiority. Carefully 

 directed experiments in which the possible effects of disuse 

 were carefalty excluded might do much to put this matter 

 upon a more satisfactory basis of observed fact. 



It has often been pointed out that reversion to mediocrity 

 places a serious obstacle in the way of the establishment of 

 new varieties when such arise sporadically. It is of course 

 clear that where the variation is merely quantitative, a 

 matter of excess or deficiency, this obstacle will not occur. 

 There will be a certain proportion of variations in excess of 

 the mean, and a certain proportion in the direction of defi- 

 ciency. The latter will be eliminated, the former selected. 

 There is no difficulty here. But if the variety.be a peculiar 

 and special one, not liable to frequent occurrence, the 

 chances against those which happen to possess it mating 

 together would be numerous, and, on the principle of blended 

 inheritance, the reversion to mediocrity would tend to obli- 

 terate the new character. On the principle of exclusive 

 inheritance this would not be so ; and if, as in the case of 

 the Ancon breed of sheep, the variety preferred to mate 

 together rather than to mate with the parent form, segrega- 

 tion would take place, and reversion to mediocrity would be 

 barred. But without some mode of segregation the sporadic 

 variety Vv^ould stand but a poor chance. 



Take in further illustration of this point the shifted eyes 

 of flat-fish. In the absence of distinct and definite evidence 

 of the fact, one may suppose that an asymmetrical disposi- 



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