VARIATION 15 
of the extreme forms. Some further account of the 
study of continuous variations will be given in 
Chapter IV. 
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. 
1. 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 
