THE LIVING MACHINE BUILDING FACTORS. 191 



years led many biologists to deny the possibility 

 of the latter. The debate which arose has con- 

 tinued vigorously, and can not be regarded as 

 settled at the present time. One result of this 

 debate is clear. It has been shown beyond 

 question that while the inheritance of congenital 

 characters is the rule, the inheritance of acquired 

 characters is at all events unusual. At the 

 present time many naturalists would be inclined 

 to think that the balance of evidence indicates 

 that under certain conditions certain kinds of 

 acquired characters may be inherited, although 

 this is still disputed by others. Into this discus- 

 sion we cannot enter here. The reason for refer- 

 ring to it at all is, however, evident. We are 

 searching for nature's method of building ma- 

 chines. It is perfectly clear that variations 

 among animals and plants are the foundations 

 of the successive steps in advance made in this 

 machine building, but of course only such varia- 

 tions as can be transmitted to posterity can 

 serve any purpose in this development. If there- 

 fore it should prove that acquired characters can 

 not be inherited, then we should no longer be 

 able to look upon the direct influence of the sur- 

 roundings as a factor in the machine building. 

 We should then have nothing left except the con- 

 genital variations produced by sexual union, or 

 the direct variation of the germ plasm as a factor 

 for advance. If, however, it shall prove that 

 acquired characters may even occasionally be in- 

 herited, then the direct effect of the environment 

 upon the individual will serve as a decided 

 assistance in our problem. 



