Chapter 35 



VARIATIONS AND ADAPTATIONS 

 IN ANIMALS AND PLANTS 



Variations (L. variare, to change) are diflferences, both structural and 

 functional, which exist between offspring of the same parents or in in- 

 dividuals of the same species. Variation also may be considered as the 

 process of changing from one organic condition to another. The ability 

 to vary is an inherent property of living organisms by means of which 

 they attempt to live more or less successfully in their changing environ- 

 ment. 



Adaptations (L. ad, to; aptere, to fit) are the result of structural or 

 functional changes on the part of an organism whereby it attempts to 

 adjust itself, directly or indirectly, to the influences of the environment 

 in order to live more or less successfully. The powers of adaptation are 

 the result of the inherent responsive ability (irritability) of living sub- 

 stance to stimuli. Since environment is changing constantly, a living 

 organism must have a corresponding ability to change in order to attempt 

 to adapt itself to these environmental changes. 



IMPORTANCE OF VARIATIONS 



Variations make it possible for individual organisms to differ from 

 each other and thus express their individualities. Educational, cultural, 

 or sociologic progress is due to the inherent abilities of living organisms 

 to vary. Differences in variations are due to (1) a difference in the 

 hereditary materials with which the organism starts its life, (2) the 

 effects of different environmental factors, external and internal, upon 

 these original hereditary materials, and (3) the interaction of the above 

 factors. 



Variations are of great importance in our studies of heredity. The 

 causes, limitations, heritability, and effects of variations must be fully 

 understood in order to draw correct conclusions in the study of heredity. 

 It can be readily seen that ignorance of variations might lead to the 



721 



