THE STATISTICAL STUDY OF EVOLUTION. 459 



Femur and tibia 81 to .89 



Femur and humerus 84 to .87 



Humerus and radius 74 to .84 



Humerus and ulna 75 to .86 



Clavicle and humerus 44 to .63 



Clavicle and scapula 12 to .16 



Stature and femur 80 to .81 



Stature and humerus 77 to .81 



Stature and fore-arm .37 



Stature and cephalic index — .80 



Length and breadth of skull 29 to .49 



Breadth and height of skull 10 to .34 



Length and capacity of skull 50 to .89 



Length x breadth x height and capacity of skull 70 to .80 



Weight and length (babies) 62 to .64 



\Veight and stature (adolescents) 50 to .72 



Right and left femur .96 



llight and left first joint of ring finger .93 



First joints of right hand, index and middle fingers .90 



First joints of right hand, index and little fingers .82 



Metacarpal phalanges, right hand, index and middle fingers. .94 



Metacarpal phalanges, right hand index and little fingers . . .89 



Strength of pull and stature 22 to .30 



Strength of pull and weight 34 to .54 



A study of this table shows us how justified was Darwin's con- 

 tention that the evolution of one organ necessarily means the evolution 

 of many parts of the body. 



The modern methods of studying evolution have still another appli- 

 cation. It is sometimes said that variation and heredity are the two 

 factors of evolution. Heredity is, however, only a special case of 

 correlated variation; a correlation between parents and offspring or 

 between any two blood relatives. So evolution is reduced to a single 

 factor — variation, simple and correlated. 



As a criticism of the new methods of studying variation it has 

 been urged that, after all, they deal not so much with the causes of 

 evolution as with the mere results. To this criticism it may be 

 rejoined that the first step toward the determination of the causes of 

 a phenomenon is a precise knowledge of the limitations and condi- 

 tions of the phenomenon itself; and this is what the quantitative 

 study of variation gives. Science has been more retarded by wasted 

 efforts to explain erroneous data than by conscientious attempts to dis- 

 cover the precise facts. For when the facts are correctly known the 

 true explanation often follows at once. Even if the explanation does 

 not follow at once the proper direction of experimentation to discover 

 causes is indicated. Statistics tell us not only the exact static condi- 

 tion of species to-day under the varying circumstances of environ- 

 ment; but they will enable us to measure precisely the results of any 

 change in environment, artificially or naturally brought about. We 



