OKLAHOMA ACADEMY OF SCIENCE 53 



These are the four fields which are most worked at the present 

 time. 



If the evolutionary problem be critically analyzed it becomes 

 apparent that our conceptions must depend upon studies of inheri- 

 tance, for the heart of the problem is the means by which the 

 transmission of characters from one generation to the succeeding is 

 accomplished. This, the present day approach to the evolution 

 problem, is the field of genetics. E. B. Wilson, one of the world's 

 greatest zologists, in his address of 1914 as president of the 

 American Association for the Advancement of Science, said,' 

 "Biologists turned aside from general theories of evolution and 

 their deductive application to special problems of descent, in order 

 to take up objective experiments on variation and heredity for 

 their own sake. This was not due to any doubts concerning the 

 reality of evolution or to any lack of interest in its problems. It 

 was a policy of masterly inactivity deliberately adopted ; for 

 further discussions concerning the causes of evolution had clearly 

 become futile until a more adequate and critical view of existing 

 genetic phenomena had been obtained." 



Modern genetics is little more than a dozen years old, but ir 

 that time it has accomplished wonders. "Inheritance includes all 

 qualities or characters which have physical basis in the fertilized 

 egg coil, . . . and which become expressed during the develop- 

 ment of the organism." Wa unders'l'and that in the germ, cell, 

 that is, the egg or sperm cell, there exist units or factors, technically 

 ca led genes, that represent every character that comes to expres- 

 sion during the later- development of the organism. Tliere rnay be 

 seen at certain stages in the division of every cell of the body, if 

 microscopi.al^y examined, definite bodies, which in general are 

 constant in size, shape, and number, and which are called chromo- 

 somes because of their tendency to staii'x dark with many dyes that 

 are used for the purpose. These chromosomes are found to be the 

 seat of the hereditary characters, and according to the present con- 

 ception the genes are arranged in linear order along these chrom.o- 

 somics. Since there are only a few chromosomes in the cell of any 

 one animal, and since the genes are very numerous indeed, it fol- 

 lows that in inheritance many characters must be bound together 

 in groups ; these groups are known as linkage groups, all the genes 

 that are located in any one chromosome being thus linked together. 

 But it sometimes happens that in the early stages of cell division a 

 pair of chromosomes will become twisted about each other, so 

 that when they separate, an exchange of material takes place and 

 each chromosome gets part of- the chromatim of the other; this is 



