BIOMETRICS 143 



and especially in his Natural Inheritance (1889), laid the 

 foundation for all modern researches of Biometrics. His 

 foremost pupil is Karl Pearson, who has made this subject 

 especially his own, and to whom we owe the name of this 

 science, Biometrics. 



II.— VARIABILITY AND NORMAL FREQUENCY CURVE. 



It is a well-known fact that Darwin based his theory of 

 Natural Selection on the existence of individual differences 

 which occur as a regular phenomenon among plants and 

 animals of any species. These variations, as they are 

 called, form, according to him, the material of all organic 

 evolution, which takes place by small insignificant steps, 

 accumulating in successive generations, and thus leading 

 to a gradual transformation of species. While the battle 

 had to be won for the principle of evolution, little attention 

 was paid to the basic material of evolution, and it is only 

 lately that variations have been investigated in a methodical 

 manner, chiefly by W. Bateson and De Vries. They dis- 

 covered that, in addition to the small individual differences 

 which occur between all members of any given species, 

 there are cases where the differences are larger, more 

 abrupt, and distinct. While the former variations are 

 called normal, fluctuating, or continuous, the latter are 

 called abnormal, definite, and discontinuous. For instance, 

 the normal differences in the stature of man are slight, and 

 range themselves easily into a graduated scale from very 

 small to very great heights ; on the other hand, the number 

 of petals in certain flowers (ox-eye daisy, primrose, etc.) 

 may vary very considerably, each additional petal meaning 

 a distinct and sudden variation of the flower in that 

 direction. De Vries has called the discontinuous variations 

 " Mutations," and maintains that Natural Selection takes 

 place only by their means, new and distinct varieties being 

 established in one bound, while the individual variations are 

 due to differences of nourishment, etc., and are ineffective 



