BIOLOGY AND PROGRESS 211 



comprehend these relations, — he must apply them 

 in his daily round of activities. 



As already indicated, there is a clear conviction 

 on the part of scientists that man's body will not 

 undergo any marked progressive changes in the 

 future. For some reason not yet perceived man's 

 body has shown but a limited range of variation 

 when compared with the flexibility of such a family 

 of fish as the Salmonidae, where one finds white- 

 fish, frost-fish, trout, charrs and salmon represent- 

 ing several distinct species; but in the Hominidae, 

 the human family, there is but one species. The 

 varieties of man are all fertile inter se which is one 

 of the criteria of species. We know nearly all 

 that we shall ever know about the physical range 

 of variation in man. To be sure refinements of 

 our knowledge will be added for many years but 

 these additions will not reveal how man can be 

 permanently modified. Thus we do not look for 

 progress to indicate how a structurally changing 

 human body can be brought about. Man must 

 get along with the kind of body that he has always 

 had. 



As long as man exists, some method must be 

 employed to keep his body going for his many 

 physiological processes all utilize energy; and the 

 changing of potential into kinetic energy is a basal 

 relation solved long ago. Man will become more 



