An Introduction to 



Heredity and genetics 



Modern Biological Laws and Theories 

 Relating to Animal and Plant Breeding 



INTRODUCTION 



Ever since the dawn of civilization attention has been 

 given to the breeding of plants and animals, as evidence 

 the numerous strains of cultivated plants and domesticated 

 animals that now exist and have been in existence for 

 many thousands of years. There seems to be no doubt 

 that all of these domesticated forms have originated from 

 wild forms. The origin of some of the forms is actually 

 known, but that of the majority is lost in the centuries pre- 

 ceding the time of written records. 



In most cases considerable differences now exist be- 

 tween the wild and the domesticated forms. The superior- 

 ity of the latter over the former has been brought about by 

 crossing and by intelligent selection of the most desirable 

 forms, according to the purpose man had in mind. 



Man's knowledge of the laws governing the production 

 of animals and plants has been gradually acquired, slowly 

 for a long time, but more rapidly as his acquaintance with 

 the organic world increased. Especially have great strides 

 been made during the last fifty years — since the appear- 

 ance of Darwin's Origin of Species (1859), when, with over- 

 whelming evidence, it was shown that organic beings are 

 the "modified descendants of earlier forms, that in some 

 way (by Natural Selection) new forms have arisen from 

 the old ones, and have given rise, in turn, to other forms.".- 



In the chapters that follow an attempt is made to 

 outline briefly the more important theories that have been 

 put forward by biologists to explain the development of 

 plant and animal life, and to summarize the information 

 gained by experimental investigation relating to inheri- 

 tance. These will be discussed with the object of showing 

 their bearing on the important problems of breeding. These 

 chapters form, therefore, an introduction to the more 

 technical courses given in the departments of Animal Hus- 



