HEREDITY AND VARIATION 



209 



found to differ somowhat, oven thougli vcM'y slip;ht.ly, both fioin 

 its parents and from its follow offspi'ing. These differences are 

 known as variations (Figs. 119 and 120) and their presence brings 

 about that variability which is so characteristic of all living things, 

 Laws of Inheritance. — The close attention given to the problems 

 of breeding by those who have been responsible for the steady 

 improvement of our domesticated animals and plants through the 



Fig. 120. — Variation in color, shape, size, and surface in the fruit of the 

 summer squash. All of these types may appear among the descendants of a 

 single individual. 



centuries has been rich in practical gains, but it has contributed 

 little to an understanding of inheritance beyond a recognition of 

 these two main facts of heredity and variation. Man has long 

 known that "like begets like" and that offspring differ among 

 themselves, and he has used this knowledge in choosing the best 

 individuals and breeding from them. In this way breeders have 

 made steady improvement, but this improvement has been 

 largely due to sharp-sightedness in seizing upon favorable varia- 

 tions rather than to a fundamental understanding of inheritance 

 which would enable the breeder to control the process and predict 

 its results. Within the last century, however, and particularly 

 within the last twenty years, notable advances have been made 



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