464 THE POPULAR SCIENCE MONTHLY 



about the central theme of human ability and its dependence upon the 

 stock. In a study of three hundred eminent English families, Galton 

 found the descent of great mental capacity to be far more intensive 

 than i» less eminent families; and found, further, that the closer the 

 blood-relationship, the greater was the number of eminent individuals. 

 Later studies, for example, Galton's own recent inquiry into the family 

 history of Fellows of the Eoyal Society, have likewise shown that the 

 person of superior mind is much more likely than the average to pos- 

 sess superior ancestors and descendants. These facts are justly inter- 

 preted as an indication that mental endowment depends in large meas- 

 ure upon direct inheritance. 



This kind of inquiry then — the kind that takes human beings in the 

 mass and applies a rough unit of measurement — reveals in a striking 

 way the importance of the hereditary factor in mental ability. How- 

 ever, the method does not constitute a science of heredity. No evolu- 

 tionist would be satisfied to know that large horses beget large horses, 

 and small horses small horses. It is the degree of likeness of some 

 particular organ, or quality, or function, or peculiarity that the student 

 of heredity now attempts to state, and to state often in numerical 

 terms. 



So the present psychological problem of heredity comes back to the 

 question of mental characters and of the best methods for their descrip- 

 tion and measurement. The psychologist may answer this question in 

 either one of two ways. First, he may fall back upon the distinctions 

 of every-day or popular psychology and say that " a good memory," 

 " sound judgment," " conscientiousness," " affability," " sentimental- 

 ity " and " industry " are mental characters, and that the way to cal- 

 culate their heritability is to take a large number of persons, related 

 and not related, estimate the eminence of these qualities in each, note 

 their distribution and derive laws of resemblance. If you find that a 

 good memory, or affability, or industry " runs in families," and is not 

 to be attributed to a common environment, you may conclude that the 

 characteristic in question is heritable. As a matter of fact, this is the 

 method that, for the most part, has been employed within the last ten 

 years; and it has been used either by biometricians themselves, or by 

 the psychologist who has followed their initiative. 



' Let me cite two or three instances. Professor Karl Pearson, of the 

 University of London, the leader of the biometrical school, collected 

 from teachers data regarding some four thousand children. Color of 

 hair and eyes and cephalic index were among the physical characters 

 graded, and conscientiousness, temper and assertiveness among the 

 mental traits. The degree of likeness between brothers and sisters was 

 found to be substantially the same for plrysical and mental qualities ; 

 in Pearson's terms, each showed a correlation of about 0.5. Again, 



