An Introduction to a Biology 



tially based on statistics of average condact. Corpuscles 

 in each other's presence are supposed to obey certain laws 

 of motion, but no explanation has hitherto been given of 

 these laws. So it is with vital units ; they vary, why they 

 vary we know not, and we explain nothing by attributing 

 it to bathmic influences. As we can predict little or nothing 

 of the individual atom, so we can predict little or nothing 

 of the individual vital unit. We can deal only with statistics 

 of average conduct. We have laws of variation and laws of 

 heredity, in themselves quite as general and as definite as 

 the majority of those we meet with in physics." 



I may perhaps take this opportunity to explain that I 

 have used the term biometric theory advisedly, and that 

 the definition of it that I have had before my eyes is not 

 merely " the application of exact statistical methods to the 

 problems of biology," ^ but the aspect of vital phenomena, 

 just quoted from the " Grammar of Science," which prompts 

 that application. 



And I believe that I am justified in including under the 

 term " biometric " both Pearson's and Galton's theories 

 which, though in one respect they are radically different, ^ 

 resemble each other in regarding heredity as a mass-pheno- 

 menon and in treating it by the statistical method. 



The Mendelian, on the other hand, w^ith a new appli- 

 cation of experiment, is a biological demon who, " perceiving '* 

 and " handling the separate " units themselves, tries to 

 find out their properties by mating them with other units. 

 But here again I need not expatiate on the closeness of the 

 parallel I have suggested w^hen w^e have these words from 

 the champion of Mendelism in this country : ^ " In the Men- 

 dehan method of experiment the one essential is that the 

 posterity of each individual should be traced separately. 



1 



Nature, Oct. 27, 1904, p. 626. 



* Karl Pearaon, Bloynetrika, Vol. 3, pp. 110-11. 



* Presidential| Address to Section D, Brit. Assoc, 1904, in Nature, 

 August 25, p. 409. 



157 



