chaptp:r XVII 



The outlook. Some unsolved prohlenis of biology. Possibil- 

 ities of larger service. 



It is as profitable for Science as for the individual to pause 

 now and then and take an inventory ; to view in retrospect 

 its successes as well as its failures, and in prospect its possi- 

 bilities and its problems — such a backward glance over the 

 pages of biology in America has been taken in the preceding 

 chapters. In closing let us draw aside the veil for a moment, 

 and view the opportunities for future service of biology to 

 man. 



The most urgent demand upon biology today is for a 

 study of the factors of evolution. In spite of Darwin, Weis- 

 mann and DeVries and the host of splendid workers who have 

 devoted their lives to a solution of this problem in the past, 

 the final answer, or answers, for there are doubtless many, is 

 still shrouded in mystery. The ultimate causes of vanation, 

 the creative power of selection, the possibility of the inherit- 

 ance of characters acquired during the lifetime of the indi- 

 vidual — these and many others are still unsolved problems. 



Closely allied to, nay, inseparable from the problem of 

 evolution is that of inheritance. Is the "unit-character" the 

 Ultima Thule of the explorer of life's mysteries? Or is it 

 in itself a little cosmos of characters acting and reacting 

 upon one another to produce the end result? Is the behavior 

 of "unit characters" fixed and immutable, like the laws of 

 the Medes and Persians, or is it subject to environmental 

 influence, yielding different results according to the condi- 

 tions imposed upon it? And what is the nature of the 

 "determiners" of these "unit characters"? Are they con- 

 stant physical or chemical entities, pereistent from generation 

 to generation of the cell, or are they variables, which pass 

 through a complex series of developmental changes beginning 

 in the fertilized egg and reaching fruition only in the adult 

 organism? Are these determiners restricted to the chromo- 

 somes or ai'e they present in the cytoplasm as well? And if 

 restricted to the former does the latter exercise no influence 

 upon them? Is the entire organism a complex of unit char- 

 acters, or is it the superficial characters alone, such as color, 



478 



