CHAPTER XXXIV 

 HEREDITY 



461. Importance of the Study. — i. To Pure Science. — 

 Xo knowledge is more fundamental than a correct under- 

 standing of the laws of heredity. Its fundamental im- 

 portance to pure science becomes evident at once when we 

 consider that, since evolution has been accomplished by 

 the descent of one organism from another, there have been 

 one or more unbroken lines of inheritance from the dawn 

 of plant life to the present. Hence, until we know the 

 laws of heredity, we cannot fully understand expression, 

 reproduction, development, variation, sex, or evolution. 



2. To Applied Science. — Correct ideas concerning he- 

 redity are absolutely essential to such phases of applied 

 science as animal and plant breeding. In the light of such 

 knowledge the breeder can avoid making useless experi- 

 ments, and can accomplish desired results more quickly, 

 more cheaply, and with greater certainty of success. 



3. To Man. — A correct knowledge of the principles of 

 heredity is vital to mankind ; no knowledge is more so. To 

 realize this, we have only to reflect that our own characters 

 are very largely the result of inheritance from our ances- 

 tors; and not only our characters, but our physical char- 

 acteristics, our vigor of mind and body, our capacity for 

 education, our susceptibility to disease, and often the 

 actual existence of some disease within our bodies or minds. 



462. Heredity Reduced to Its Lowest Terms. — We may 

 study heredity under the very simplest conditions in the 



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