228 Heredity and Environment 



physiologically related to other cells and to other plasms, and 

 similarly there is no doubt that the germ plasm although very 

 stable can and does change its constitution under some rare 

 conditions. But in the main the germ plasm theory is accepted by 

 the great majority of biologists to-day, and recent work in 

 genetics and cytology has brought many confirmations of this 

 theory. 



Distinction between Hereditary and Acquired Characters. — As 

 long as it was believed that the developed characters of an or- 

 ganism could be transmitted as such to its -descendants it was cus- 

 tomary to speak of developed characters as hereditary or ac- 

 quired and to talk of the inheritance or non-inheritance of acquired 

 characters. This distinction is not a logical one for all developed 

 characters are invariably the result of the responses of the ger- 

 minal organization to environmental stimuli ; and of course no 

 developed character can be purely hereditary or purely environ- 

 mental. But when a given character arises in many individuals 

 of the same genotype under different environmental conditions it 

 is probable that heredity, which is the constant factor in this 

 case, is also the determining factor for that character. On the 

 other hand if a character develops in response to peculiar stimuli 

 and does not appear in other individuals of the same genotype in 

 which such stimuli are lacking it is said to be an environmental 

 or acquired character. In fine, inherited characters are those 

 whose distinctive or differential causes are in the germ cells, 

 while acquired characters are those whose differential causes are 

 environmental. 



Statement of Problem. — Briefly stated the question of the in- 

 heritance of acquired characters is this : Can the differential 

 cause of a character be shifted from the environment to the germ 

 plasm? Can peculiarities of the environment which influence 

 the development of somatic characters so affect the germ cells 

 that they will produce these somatic characters in the absence of 

 the peculiar environment? Can the characteristics of a developed 

 organism enter into its germ cells and be born again in the next 



