A QUESTION OF WORDS 13 



the secondary or directive factors which operate upon the raw 

 materials of progress which variabiHty supphes — notably 

 Selection and Isolation — is not relevant at present. 



§ 4. ^ Question of Words 



In every discussion with a serious purpose it is important that 

 there should be clearness as to the terms used. We must, 

 therefore, ask the reader to notice our definition of the chief 

 terms. Thus by " heredity " we do not mean the general fact 

 of observation that like tends to beget like, nor a power making 

 for continuity or persistence of characters — to be opposed to the 

 power of varying — nor anything but the organic or genetic relation 

 between successive generations ; and by " inheritance " we mean 

 *' organic inheritance " — all that the organism is or has to start 

 with in virtue of its hereditary relation to parents and ancestors. 

 We do not forget that for man in particular there is an external 

 heritage — a social inheritance — which counts for much. By 

 innate or inborn we mean all that is potentially implied in the 

 fertilised egg-cell ; by the expression of the inheritance we 

 mean the realisation of inborn potentiahties in the course of 

 development in an appropriate environment ; by a congenital 

 character {pace many medical writers) we mean one demonstrable 

 at birth, which is not necessarily germinal, being often due to 

 peculiarities — e.g. infection or poisoning or mechanical injury 

 during pre-natal development. Thus, tubercle may be con- 

 genital, but it is never inherited. By modifications or acquired 

 characters we mean structural changes in the body induced 

 by changes in the environment or in the function, and such that 

 they transcend the hmit of organic elasticity, and therefore 

 persist after the inducing conditions have ceased to operate. 

 By a variation we mean not any observed difference between 

 offspring and parent, between an individual and the mean of 



