CHAPTER I 

 INTRODUCTION 



It should be realized that genetics is a natural out- 

 growth from the study of organic evolution. The con- 

 ception of evolution began as a speculation, but became 

 scientific in connection with the work of Lamarck and 

 Darwin. In such work the method used was that of 

 observation and inference. Facts were observed and 

 an explanation was devised that would relate them. 

 Resemblances and differences among species were 

 noted, and it was inferred that these indicated degrees 

 of relationship. It was assumed that closely related 

 species must have had a comparatively recent common 

 ancestry and that more distantly related species must 

 have had a more remote common ancestry. Through 

 comparisons of structure and of geographical distribution 

 systems of phylogeny have been inferred, and an outline 

 of the evolution of the plant and animal kingdoms has 

 been the result. All of these conclusions are based upon 

 comparison and inference. 



This method reached its extreme application in the 

 work of Darwin, whose observations included a range 

 of forms and an extent of time unequaled by any pre- 

 ceding student of evolution. It may be said that in 

 Darwin's work the method of comparison and infer- 

 ence reached the hmit of its possibilities. The students 

 of evolution were chiefly concerned with explaining 

 the changes that resulted in phylogeny. In other words, 



