GENETICS 419 



strates that species are capable of change but also pro- 

 vides a clue to the method whereby species may have 

 developed in a state of nature. 



Genetics. — In recent years breeding experiments have 

 been carried on by the trained biologist, not so much for 

 the purpose of bringing to a high state of development 

 some particular character in an organism as to determine 

 the underlying causes of variations and the manner of 

 their inheritance. This new science of genetics, as it is 

 termed, is thus largely a study of heredity controlled and 

 analyzed at every stage. 



A species of animal or plant is selected for the experi- 

 ment whose ancestral history or pedigree is well 

 known. Its development, at least in a general way, is 

 traced out, and the behavior and structure of the germ 

 cells is determined with a high degree of accuracy. The 

 different kinds of variations which occur during the 

 course of the experiments are also recorded, and where 

 these are inherited the mechanism determining their in- 

 heritance is analyzed by the most highly refined methods 

 known to the scientist. The determination of sex, and the 

 relation this phenomenon bears to heredity are also 

 phases of the general subject of genetics. Paleontology, 

 geographical distribution, classification, and the other sci- 

 ences previously mentioned supply proof that evolution 

 has taken place. Artificial selection demonstrates that 

 evolution is still possible and can be guided by the 

 breeder, and the results of studies in genetics have enabled 

 the biologist to form a far clearer picture of the mechan- 

 ism of evolution than was known in Darwin's time. 



