INHERITED VARIATIONS AND FITNESS PROBLEMS 



465 



THE AGE-INCIDENCE PRINCIPLE OF INVESTIGATION 



The age-incidence finding revealed a new and useful principle in evaluat- 

 ing inherited variations, which I have called the age-incidence principle of 

 investigation. This principle is firmly grounded in the relation of heredity 



THE AGE INCIDENCE OF SCAPULAS TYPES 

 APPROXIMATE RELATIVE PESCENTASES 



10 20 30 40 SO 60 TO 80 90 100 



AGE PEEI0D5 



w m .w.seave& 

 Graph 1. Indicating the Magnitude of the Relation of Inherited Variations in 

 General and Scapular Types in Particular to Longevity 

 It portrays the approximate relative percentages of convex and scaphoid types in suc- 

 cessive age periods from fifteen to sixty-five years. It serves to explain the age incidence 

 of these types by the selective death rate expressed in the relation of heredity to longevity. 



to longevity .... a relation long recognized by physicians, biologists, actu- 

 aries and biometricians. It was Oliver Wendell Holmes who said to live to 

 be old, one should be circumspect in the choice of one's ancestors. The in- 

 vestigations of Beeton and Pearson (41), Bell (42), Ploetz (43), Forsyth (44), 



