CHAPTER XV. 



REPRODUCTION, PUBERTY AND LONGEVITY. 



Nearly a century ago Lamarck told us that ''the development of 

 organs and their force, or power of action (functional capacity) 

 are in direct relationship to the employment of these organs" and 

 that "all that has been acquired or altered in the organization of 

 individuals during their lives is preserved by generation, and trans- 

 mitted to individuals which spring from those which have under- 

 gone these changes." In stating his laws Lamarck laid particular 

 stress on the fact that acquired changes are proportional to the 

 activity of the organs and the length of time during which the 

 activity was continued, and he states that the transmission of ac- 

 quired characters takes place after the acquirement. By the very 

 simple process of comparing the offspring of individuals "which 

 have undergone these changes" in different degrees, we have found 

 that "the development of organs and their force, or power of action" 

 in the offspring are "proportional to the length of their employ- 

 ment" in parents, exactly as Lamarck told us they were. 



This process of comparison has been carried through various 

 animals, the different races of men, and different men in the higher 

 races. Taking the series as a whole, we find that the inheritance 

 by offspring, if not absolutely proportional to ancestral acquirement 

 by use, is so nearly proportional that we are not able to point out 

 the discrepancies. 



THE FACTORS OF ANCESTRAL USE. 



Ancestral use is made up of two factors, activity, and length 

 of time during which activity is continued before reproduction. 



