24 GENETICS 



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veloped within recent years. Sir Francis Galton, Dar- 

 win's distinguished cousin, may be regarded as the 

 pioneer in this field of research, while Karl Pearson and 

 his disciples are representatives of the modern school 

 of biometricians. 



Although mathematical analysis of biological data 

 when not sufficiently ballasted by biological analysis 

 of the same facts may sometimes lead the investigator 

 astray, yet often the only way to formulate certain 

 truths or to analyze data of some kinds is by resort to 

 statistical methods. Biometricians are quite right in 

 insisting that it is frequently necessary to go further 

 than the fact of variation, which may be apparent 

 from the inspection of an individual case, and to deal 

 with cumulative evidence as presented through statisti- 

 cal analysis. 



In matters of heredity, however, facts as they occur 

 in single cases and definite pedigrees seem to offer a 

 more hopeful line of approach than statistical generali- 

 zations. It is better to become acquainted with the real 

 parent than to evolve a hypothetical "mid-parent" 

 mathematically. In this connection it is well always to 

 bear in mind the warning of Johannsen, himself a past 

 master in biometry, when he writes : "3f it Mathematik 

 nicht als Mathematik treiben wir unsere Studien." 



6. FLUCTUATING VARIATION 



With respect to any measurable character there 

 are bound to be deviations from an average condition. 

 According to the mathematical laws of chance these de- 



