482 EVOLUTION, GENETICS, AND EUGENICS 



COEFFICIENTS OF CORRELATION BETWEEN TOTAL 

 RIDGE COUNTS OF FIVE FINGERS 

 OF EACH HAND 



Correlation between right and left hands of same 

 individual r=o. 93 + 0.01 



Correlation between right plus left hands of identical 



twins r = 0.95 ±0.01 



Correlation between right plus left hands of fraternal 



twins r=o.46 + o.o8 



Correlation between right plus left hands of 30 pairs 



of brothers and sisters (Bonnevie) r= 0.59 + 0.08 



Correlation between right plus left hands of 30 un- 

 related individuals (Bonnevie) ^ = 0.27 + 0.12 



It will be seen that identical twins are even more alike in total 

 ridge counts of finger patterns than are the two sides of the bodies of 

 single individuals. This is in itself strong proof of the hereditary 

 character of finger patterns. Fraternal twins are no more alike (in this 

 series not as much alike) as are ordinary sibs. The extremely close 

 resemblance between identical twins should be contrasted with the 

 very low correlation in unrelated individuals. The slight positive cor- 

 relation in unrelated individuals may be taken as a residuum of racial 

 heredity. 



In contrast with finger patterns, which everyone knows are fixed 

 at birth and do not change throughout life — a fact that makes them 

 valuable as an aid in personal identification — let us examine the degree 

 of correlation in mental qualities as exhibited by groups of varying 

 grades of relationship. Taking the Intelligence Quotient (I.Q.) as a 

 measure of mental capacity, the following table was worked out by 

 Kohn, a capable German student of twins: 



COEFFICIENTS OF CORRELATION BE- 

 TWEEN INTELLIGENCE 

 QUOTIENTS (I.Q.) 



Identical twins o . 90 



Fraternal twins 0.59 



Sibs o. 50 



Sisters 0.47 



Brothers, o . 46 



It is highly significant that mental differences show substantially 

 the same grades of correlation as do the finger patterns, which are 

 generally admitted to be purely hereditary. Various other authors, 

 including our own local investigators, have found essentially the same 



