A CRITICAL EXAMINATION 19 



2. The Mendelian. 



From a methodological standpoint the Men- 

 delian mode of studying inheritance is a statistical 

 method. The fire-eating Mendelist, if any more 

 such exist, to whom biometry is anathema, may 

 object to this statement, but a little consideration 

 will show it to be true. In actual fact, the most 

 essential methodological difference between the 

 biometric and the Mendelian methods is one which 

 has hitherto been quite generally overlooked, so 

 far as I am aware. It is found merely in the fact 

 that the biometric method studies the ancestry of 

 the individual, while the Mendelian method studies 

 the individual's progeny. One goes backward on 

 the pedigree ; the other goes forward. The net- 

 work of descent may be likened to two pencils 

 of light rays both of which focus in the individual. 

 The ancestral pencil converges upon the individual. 

 The progenial pencil diverges from the individual. 

 The practical consequences to the investigator 

 of the fact that quite different possibilities are 

 opened, according to which one of these two 

 possible ways of studying genetic relationships 

 one chooses, are extremely interesting, but time 

 is lacking to go into their discussion in detail here. 

 How profound in general they are is sufficiently 

 indicated by comparing the achievements, in the 

 way of advancing our knowledge of the hereditary 

 process, of the biometric method on the one hand 

 and the Mendelian on the other hand. It is 



