WILLIAM G. STEVENSON. 65 
enable an individual to become ‘‘ eminent’”’ or even ‘ il- 
lustrious.”’ 
Heredity is, therefore, the silent conservator and di- 
recting factor of mental life; it is that inborn power of 
organization which enables ‘‘one out of a million’’ to 
become a genius, and to surmount all obstacles and neu- 
tralize every repressive influence, while others who have 
not this exalted birthright fall by the way and lose 
their individuality in the vast throng of a common 
humanity. 
That there is a profound principle of truth involved in 
the question of heredity cannot be denied, and that the 
factor of inheritance is the most essential of any which 
enters into the complex equation of mind as well as of 
body, is a well-established fact; but it is not the only 
factor which determines mental expression, nor can a 
complete classification of known facts be made from it 
alone. Heredity explains the existence of a general 
nervous constitution, a brain-fiber, having definite apti- 
tudes or ‘‘ organic dispositions,’ which are transmitted 
from parent to offspring, securing thereby not only a 
continuity, but a conservation of psychical as well as of 
physical properties ; but the special way in which this 
mental aptitude shall show itself is largely dependent 
upon external influences or an unexplained spontaneity. 
Organization limits the influence exerted by environ- 
ment, while environment limits and modifies the devel- 
opment of the capacities of the organization. 
The explanation of genius through the operation of 
the biologic law of heredity is very satisfactory so long 
as antecedent and sequence bear to each other defi- 
nite and ascertainable relations ; but trouble begins 
when the genetic record fails in its apparent unity—as 
when genius and mediocrity have kinship. 
Whence came the genius of Phidias, which enabled 
him with such immortal art to createin carved ivory and 
