VARIATION 15 



oi the extreme forms. Some further account of the 

 study of continuous variations will be given in 

 ChapterJV. 



A second kind of variation is variously known as 

 abnormal, definite* and discontinuous variation, and 

 includes what are known as sports and mutations. 

 Such variations, as is indicated by the terms applied 

 to them? involve definite differences usually of con- 

 siderable amplitude. A good example of a discon- 

 tinuous variation would be afforded by the appear- 

 ance of a child having six fingers in a family in which 

 this abnormality was not previously known to occur. 

 We shall pursue the discussion of discontinuous varia- 

 tion and of the methods of perpetuation of the types 

 which thus arise in Chapters V. and VII. 



A short account of the historical development of the 

 theory of organic evolution is given in Chapter II. As 

 alternatives to the theory of the special creation of 

 each individual species, a number of more or less crude 

 speculations were indulged in by the philosophers of 

 ancient Greece. Passing to more recent times, three 

 distinct accounts of the method of origin of specific 

 differences have been proposed almost within the last 

 century, and each of these theories still finds a number 

 of supporters. 



i. The view of Lamarck, published first in 1801, and 

 in an enlarged form in 1809, was briefly as follows ; 

 Noticing that the organs of men and other animals are 

 increased and strengthened by use, and particularly 

 by conscious use, Lamarck assumed that this effect 



