202 HEREDITY AND ENVIRONMENT 



stronger or weaker build, is inherited, and 

 while diminished resistance is not the direct 

 cause of tuberculosis it is a predisposing cause. 

 The same is probably true of many other 

 diseases, the immediate causes of which are 

 extrinsic, while only the more remote, or pre- 

 disposing causes, are hereditary. 



(c) Physiological peculiarities are inherited 

 as well as morphological ones ; indeed function 

 and structure are only two aspects of one and 

 the same thing, namely organization. For all 

 morphological characters there are functional 

 correlatives, for functional characters morpho- 

 logical expressions, and if the one is inherited 

 so is the other. But there are certain char- 

 acters in which the physiological aspect is 

 more striking than the morphological one. 



For example, longevity is a physiological 

 character which is undoubtedly dependent 

 upon many causes, but in the case of species 

 which differ greatly in length of life there can 

 be little doubt that we are dealing with an in- 

 herited character. The great differences in 

 the length of life of an elephant and a mouse, 

 of a parrot and a pigeon, of a cicada and a 



