46 HEREDITARY CHARACTERS 



The characters of the adult are not, however, all of the 

 same kind, at any rate among the higher animals. Some of 

 them are inborn, and under normal conditions of nourish- 

 ment will develop without any other stimulus. Others 

 depend upon various kinds of stimuli to produce them. 

 We will take a concrete case as an example the possession 

 of two arms with the normal complement of bones and 

 muscles is an inborn character in man. By exercise he is 

 able to increase the size of the muscles in one or in both 

 arms, and even the size of the bones if the exercise is begun 

 early and continued long enough. These are not inborn but 

 acquired characters, often called modifications. They are 

 due to stimuli acting upon the cells derived from the 

 fertilised ovum. The potentiality of producing them is 

 present, but only comes into action in the presence of 

 suitable stimuli. Such characters will not be produced 

 without the stimulus, as we see from the converse case. 

 A man might not use one of his arms at all through disease 

 or accident, and in this case the muscles and bones will 

 not be developed to anything approaching the normal 

 extent. If he uses his arms less than is usual with men, 

 his muscles will be less developed than is normally the case. 



The failure to produce acquired characters does not 

 mean that the potentiality of producing them is absent. 

 Given similar stimuli the offspring will produce the acquired 

 characters of the parent, very often with a greater degree of 

 accuracy than the inborn characters. Leaving this question 

 for the moment, we shall consider the nature of inborn and 

 acquired characters a little further. 



Inborn characters are those due to the potentiality of the 

 ovum to develop along certain lines under normal conditions 

 of nourishment and when protected from injury. They are 

 the characters that are developed merely by nourishment 

 irrespective of any other stimulus. It must be clearly 

 understood that the inborn characters do not necessarily 

 include all the characters that are present when the indi- 

 vidual is born, for environment may have acted upon the 



