438 EVOLUTION AND GENETICS 



Conversely an acquired character or adaptive response will 

 appear in every generation if the proper stimulus is available. 

 As long as the same conditions obtain, the character will appar- 

 ently be inherited because it will appear in all individuals. It 

 appears during the independent life of the individual, and its 

 appearance is directly associated with an external condition, but 

 these things are no less true of many of our inherent structures. 

 Such a character is therefore fundamentally similar to inherited 

 characters, save only that the heritage in no case provides the 

 stimulus for its development. 



Permanence of a character is due to permanence of the con- 

 tri})uting factors, heritage and environment. Every character has 

 a basis in the heritage which will be handed down from generation 

 to generation as a part of the normal functions of the living sub- 

 stance, but to the same degree every character depends for its 

 appearance upon the presence of the proper condition in the 

 environment for the normal response of this heritage. How then 

 can a change come about in the heritage? 



The Process of Evolution. In answer to this question two 

 interpretations may be based on the facts thus far set down: 



1. The power of an organism to develop any character is a 

 part of its heritage. Whatever the nature of the character, it is 

 a product of genes derived from the germ cells of the previous 

 generation and some outer stimulus. Hence even so-called 

 acquired characters may be regarded as an expression of hereditary 

 qualities resident in the germ plasm from which the individual 

 arose. If an existing individual acquires a character, then the 

 germ cells contained genes with the power to produce such a 

 character under the proper stimulus. The parents which produced 

 the germ cells therefore had genes with the same power, and so, 

 step by step, the idea can be carried in either direction through 

 successive generations, even back to ancestral species. 



This interpretation, carried to its logical extreme, would include 

 the idea that even the most primitive living matter possessed the 

 inherent ability to produce any of the characters of existing ani- 

 mals in response to the proper stimuli. To a certain extent this 

 must be as true as evolution, but it would require great credulity 

 to believe that an amoeba-like ancestor could develop the char- 

 acters of man in a generation if given the proper surroundings. 

 The view becomes acceptable only through recognition of the 



