14 THE CHARACTERS OF LIVING BEINGS 



one stimulus, some under another, and some under a third, and all 

 developing in proportion, the infant gradually becomes adapted to 

 the environments of the child and the adult. If he be injured, 

 development begins by stoppage of the blood-flow and continues till 

 growth is complete and a scar forms. Since every one is injured atone 

 time or another, without this healing life would be impossible under 

 conditions normal for the species. As we have just seen, growth 

 under the stimulus of use is also a part of normal development- 

 The human being cannot become a normal adult, fit for the struggle 

 of existence, without it. 



27. It is clear then that all characters that it is possible for the 

 individual to develop are equally rooted, as it were, in the germ- 

 plasm. Manifestly no character is more closely or less closely 

 connected with it than any other. But the traits which develop 

 under the stimulus of nutriment have two characteristics which 

 have so impressed students of heredity that attention has been 

 especially concentrated on them. 



28. First, since no individual can develop without food as 

 material for growth, the stimulus of nutriment is always present ; 

 and, therefore, if the individual lives long enough, all the characters 

 that arise under its influence inevitably appear unless prevented 

 by injury. 1 On the other hand, characters, which arose in the 

 parent under the stimulus of injury or use, may not arise in the 

 child, for similar stimuli may not be received. Thus the only 

 effect of injury which inevitably appears in the human being is the 

 navel. Other scars are not reproduced unless, as is unlikely, 

 exactly similar injuries are received by parent and child. In 

 every normal child and adult certain effects of use (e.g. the 

 muscular development of the limbs) are always present, but 

 though in practice we recognize them as effects of use (for the 

 physical and mental exercises we give our children are nothing 

 other than conscious attempts to develop them in this way), yet in 

 theory they are seldom recognized as such. Like other people, 

 students of heredity tend to think in compartments, and in their 

 discussions they have usually argued as if reactions to use were 

 limited to such exceptional and trivial developments as the extra 



1 This statement is not quite correct. Thus, though male characters are 

 latent in the female and vice versa, and though they arise under the stimulus of 

 nutriment, they do not develop. The individual has two sets of sexual characters, 

 the development of one of which is a bar to the development of the other. But, 

 apart from such cases of alternative reproduction in which the development of 

 one character prevents the development of another, the statement that characters, 

 which arise in response to the stimulus of nutriment inevitably appear is true. 



