304: THE WHENCE AND THE WHITHER OF MAN 



ously and correspondingly. Correlation and combina- 

 tion are just as essential as variation. And evolution 

 often demands the disappearance of less fit structures 

 just as much as the advance of the fittest. Says Os- 

 borne, " It is misleading to base our theory of evolution 

 and heredity solely upon entire organs ; in the hand 

 and foot we have numerous cases of muscles in close 

 contiguity, one steadily developing, the other degen- 

 erating." Weismann offers the explanation that " if 

 the average amount of food which an animal can as- 

 similate every day remains constant for a considerable 

 time, it follows that a strong influx toward one organ 

 must be accompanied by a drain upon others, and 

 this tendency will increase, from generation to genera- 

 tion; in proportion to the development of the growing 

 organ, which is favored by natural selection in its 

 increased blood-supply, etc. ; while the operation of 

 natural selection has also determined the organ which 

 can bear a corresponding loss without detriment to 

 the organism as a whole." * 



Here again natural selection of individuals, not the 

 diminished supply of nutriment, has to determine 

 which of many muscles shall be poorly fed and which 

 favored. But natural selection can favor special 

 organs only indirectly through the individuals which 

 possess such organs. Variation is fortuitous, and there 

 is nothing, except natural selection, to combine or 

 direct them. And, I think, we have already seen that 

 any theory which neglects or excludes such directing 

 and combining agencies must be unsatisfactory and 

 inadequate. Weismann has promised us an explana- 

 tion of correlation of variation in accordance with his 



* Weismann, Essays, p. 88. 



