SCIENTIFIC RESEARCH 257 



like those who have just effected a landing upon a new con- 

 tinent, whose supply camps are established, whose ax-men 

 are out, and who are beginning the march. This is a field 

 of investigation where discoveries are so new that men have 

 not yet grasped their importance nor set the facts to work 

 in ways to suit their needs. This is a problem of the future, 

 and as such appeals more strongly to imagination. 



The fact of hereditary resemblance must have been recog- 

 nized since man first gave attention to the breeding of domes- 

 ticated animals, or first saw that his offspring were like him- 

 self. But heredity remained rather the plaything of the 

 philosopher than the problem of the scientist, until the man- 

 ner of individual generation had become established and the 

 germ-cells recognized as its physical basis. All the earlier 

 work upon reproduction and development, all the investi- 

 gations which centered around the discussion of spontaneous 

 generation, all the studies which led to the cell-theory were 

 necessary to establish our present position, and to give the 

 modern investigation of heredity its point of departure. 

 With these things behind it, heredity has become a subject 

 of prime interest in present-day biology, and only in the last 

 quarter century has our attack begun. 



Two men stand out as pioneers of the recent advance 

 Gregor Mendel, whose work was the earlier done but the later 

 known; and Francis Galton, who should be credited with 

 collecting valuable data and with arousing public interest 

 by his eugenic propaganda, although his laws of heredity 

 now seems of small value. 



Without attempting an explanation of either the Galto- 

 nian or the Mendelian theory of heredity, a word may be said 

 in illustration of an essential difference between the two. 10 

 Most of us are familiar with the tables, published by insur- 

 ance companies and stating the expectation of life for a man 

 at a given age. You are, say thirty years old. The table 



10 The cellular aspects of Mendelian heredity have been briefly discussed in 

 Chapter VII, pp. 130-44. 



