56 THEORIES OF HEREDITY AND VARIATION. 



change can be explained by the known means of congenital varia- 

 tion and selection, it is unreasonable to attribute that change to the 

 inherited result of use or disuse, while at the same time they admit 

 that if any change can be shown which is explained by use and dis- 

 use and is inexplicable by congenital variation, then their theory 

 falls to the ground. The introduction of the word "congenital" is 

 the key to the whole controversy, because it is universally admitted 

 that all change is due to variation. The only question is the cause 

 of variation. 



Weismann does not fully explain how variations occur, but he 

 assumes that the two uniting cells vary somewhat in size, in form, 

 in chemical formation, or in manner of uniting, and they thereby 

 cause a variation in the resultant being. This kind of variation is 

 called congenital variation. That congenital variation exists in 

 some form is shown by the variations in twins, and in the differ- 

 ences among the different individuals in a litter of puppies, kittens 

 or pigs. 



CONFLICT OF THEORIES. 



We thus have two theories which conflict with each other and 

 neither of which has been fully and satisfactorily demonstrated. 

 The issue between them is sharply defined, and consists of the ques- 

 tion as to whether or not acquired characters are inherited and thus 

 become congenital. If the answer to this question had only an 

 academical interest, or if only related to the animals and plants 

 with which man has to deal, then it would not be very important 

 whether the question were answered or not, as these animals and 

 plants may be dealt with in a satisfactory manner by selection. But 

 as it also involves man, and as we cannot use selection by killing 

 off the poor specimens of humanity and breeding only from the best, 



