254 EFFECTS OF SEXUAL REPRODUCTION. 



PERSISTENCY OF ADVANCED AND RETROGRADE STEPS. 



If a son conceived by a functionally active parent when at the age 

 of 50 reverts to the normal condition and himself produces a son 

 when at the age of 30, this son in the third generation will be, like 

 the one in the second generation, an advance upon the first but not 

 on the second, and the same advance will be maintained from gen- 

 eration to generation. Thus a single step in advance w T ill constitute 

 a step in advance through succeeding generations, and a single 

 retrograde step will cause the retrograde condition to be trans- 

 mitted through an indefinite number of generations. As, however, 

 each individual is the product, not of one parent but of two, each 

 step in one direction will be divided among a number of individuals 

 or neutralized by a step in the opposite direction unless two steps 

 in the same direction happen to unite. 



INHERITANCE BY SEX. 



The rule relating to this appears to apply to all characters which 

 appear in the individual after the age of puberty, irrespective of 

 whether they arise congenitally or are the result of development 

 due to voluntary actions of ancestors. By characters which arise 

 congenitally I mean characters such as the beard on man, orna- 

 mental plumage on birds, and all of those forms which are in no 

 way connected with the volition of the individual. Such characters 

 have been pretty fully dealt with by Darwin and need not be further 

 referred to. 



Acquired characters are those which are enlarged, developed 

 and strengthened by functional activity, or are degenerated by the 

 lack of such activity. The amount of such development or degen- 

 eracy is measured by the time during which the process continues,. 



