A CRITICAL EXAMINATION 21 



but they are offspring individuals, not ancestral. 

 The generations which the Mendelist discusses 

 are, in Bateson's now universally adopted ter- 

 minology, the filial generations. From the stand- 

 point of mathematics Mendelian statistical 

 methods are crude and simple. Mendelism has 

 unfortunately had no Karl Pearson to work out a 

 special statistical technique directly adapted to 

 the requirements of its data. Such a special 

 technique may, however, be expected slowly to 

 develop as time goes on. 



I should like to digress here a moment to dis- 

 cuss a particular instance of the crudity of current 

 Mendelian mathematics. In recent developments 

 of Mendelian theory it has been a common prac- 

 tice to assume the existence of multiple factors 1 

 as the causal agents of a single character. There 

 can be no a priori logical objection to this pro- 

 cedure. Its mathematical dangers are not usually 

 perceived, however. Viewed as a logical method 

 the multiple factor hypothesis is simply the well- 

 known mathematical procedure of increasing the 

 number of constants of a theoretical equation 

 for the purpose of making a better "fit" to the 

 data (in this case the observed ratios). But any 

 one expertly acquainted with the general theory of 



1 This hypothesis was first used, at least on any considerable scale, 

 by Nilsson-Ehle, " Kreuzungsuntersuchungen an Hafer und Weizen." 

 Lunds Univ. Arsskr., N. F. Afd. 2, Bd. 5, pp. 1-122, 1909. It has 

 since been widely adopted by other Mendelian workers. 



