CHAPTER VIII 



CONTINUOUS AND DISCONTINUOUS VARIATION AND 



HEREDITY 



The two terms continuous and discontinuous variation refer 

 to the succession or inheritance of the variations rather than 

 to the actual conditions amongst a group of individuals liv- 

 ing at the same time ; but this distinction has only a subor- 

 dinate value. The term fluctuating, or individual variation, 

 expresses more nearly the conditions of the individuals of a 

 species at any one time, and the continuation of this sort of 

 difference is the continuous variation spoken of above. The 

 discontinuous variations are probably of the same nature as 

 those that have been called mutations, and what Darwin some- 

 times called sports, or single variations, or definite variations. 



Continuous Variation 



If we examine a number of individuals of the same species, 

 we find that no two of them are exactly alike in all particulars. 

 If, however, we arrange them according to some one character, 

 for example, according to the height, we find that there is a 

 gradation more or less perfect from one end of the series to the 

 other. Thus, if we were to take at random a hundred men, and 

 stand them in line arranged according to their height, the 

 tops of their heads, if joined, would form a nearly continuous 

 line ; the line will, of course, incline downward from the 

 tallest to the shortest man. This illustrates individual varia- 

 tion. An arrangement of this kind fails to bring out one of 

 the most important facts connected with individual differences. 



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