Cook: Reticular Heredity 



347 



stands in a more effective relation with 

 general ideas of evolution and heredity 

 than any of the character-concepts that 

 have been based on the wholly hypo- 

 thetical "units." There is no objection, 

 of course, to particularizing the charac- 

 ters in any way that the facts warrant, 

 or to recognizing any ascertained rela- 

 tions to cheinical substances or to 

 physical conditions, but all this can be 

 done without abandoning the general 

 idea of multiple descent and multiple 

 transmission of alternative ancestral 

 characters. 



CONCLUSIONS. 



The Mendelian theory of heredity 

 may be described as monogenic because 

 it assumes the transmission of only one 

 set of gens or character-units in each 

 germ-cell. A polygenic theory is re- 

 quired to account for the fact that latent 

 or suppressed characters are trans- 

 mitted, as well as those that are brought 



into expression. The polygenic nature 

 of heredity is also indicated by the fact 

 that mutative changes of expression 

 usually affect many characters at once, 

 instead of single characters. A further 

 advantage of the polygenic conception 

 is that it allows characters to be brought 

 into analogy with ancestral lines that 

 form the network of descent of the 

 species. 



The assumption that characters are 

 pre-existent in the protoplasm of germ- 

 cells as discrete particles or independent 

 units of any sort is not justified by 

 observation or by logical necessity. 

 Equally convenient and more truly 

 biological methods of thinking about 

 the problems of heredity can be devel- 

 oped by recognizing the relation of 

 heredity to the network of descent of 

 the species. This conception allows 

 characters to be thought of as repre- 

 senting lines of descent instead of as 

 discrete particles in the protoplasm. 



Value of a Knowledge of Heredity 



It seems to me that no kind of study can be made to bear intellectual fruit of 

 nearly such value as the study of heredity. It lies at the root of every science 

 and every study connected with life from botany and zoology to medicine, soci- 

 ology or pedagogy. Who knows it not knows not life except in its superficial 

 aspects. He may be a student of philosophy or a worker in biological science, 

 but in these days when heredity enters so much into philosophy and links together 

 so many biological sciences, he cannot be a very effective thinker or worker. It 

 furnishes a master-key to the more tremendous events of history, and is our only 

 hope against disasters that loom great and terrible in the near future. It goes 

 deep down to the springs of human life, and thought, and conduct, and explains 

 why some nations are inheriting the earth and the fruits thereof, while others are 

 dying physically or mentally. The philanthropist must know something of this 

 science or he will grope in the dark. The statesman must know something of it 

 or he may labor in vain. Transcending all else in importance is the educational 

 value of heredity. No nation in which a knowledge of it was widespread could 

 possibly be stupid or brutal. The habits of thought which must be brought to 

 its study are exactly those which counteract best the tendencies which have plunged 

 so many nations into their Dark Ages. So few are the essential facts of heredity, 

 but so prolonged, close and accurate must be the reasoning founded on them, that 

 no great strain is placed on the memory while the reflective faculties are exercised 

 in the highest degree. So largely would the student's learning link up with the 

 subsequent experiences of his whole life that little would be forgotten, and a sure 

 foundation would be laid for a clear and wide intellectual outlook. — G. Archdall 

 Reid: The Principles of Heredity (1904). 



