GENETICS 



CHAPTER I 



INTRODUCTION 



1. THE TRIANGLE OF LIFE 



WITHIN a generation the center of biological inter- 

 est has gradually been swinging from the origin of 

 species to the origin of the individual. The nine- 

 teenth century was Darwin's century. His monu- 

 mental work "On the Origin of Species by Means of 

 Natural Selection," which appeared in 1859, not only 

 dominated the biological sciences but also influenced 

 profoundly many other realms of thought, partic- 

 ularly those of philosophy and theology. 



Now, at the beginning of the twentieth century, 

 a particular emphasis is being laid upon the study 

 of heredity. The interpretation of investigations 

 along this line of research has been made possible 

 through the cumulative discoveries of many things 

 that were not known in Darwin's day. Trained 

 students have been patiently and persistently bend- 

 ing over improved microscopes, untangling the 

 mysteries of the cell, while an increasing host of in- 

 vestigators, inspired by the Austrian monk Mendel, 

 have been industriously devoting their energies to 



