1897.] The Biologie Origin of Mental Variety. 11 
many difficulties; and why it is imperative that its several 
propositions should henceforth be taken to heart in all prac- 
tical investigations both of Biology and of Psychology. 
By way of establishing the roads of sound attack, certain 
false paths must be pointed out that, heretofore, have continu- 
ally led our subject to obscurity and to contempt. Some of 
the errors here indicated have been made by Biologists, and 
others by Psychologists; but most of them are made by bot 
alike. Biologists are wont either to underrate the part that 
mind, or its physical equivalent plays in evolution, or to read 
into it, everywhere, the same world of psychic life that we our- 
selves experience. The doctrine of Parallelism is responsible 
for the first mistake ; for in conceiving that all conduct must be 
accounted for within physical forces alone, there is a tendency 
to fail of full recognition of the facts themselves. The marvel- 
ous variety of our mental life is nearly sure to be left out of 
practical account. Nor is it any excuse for this to say that our 
notions of “ molecular differences” and “specific energies” are 
vague; for once having adopted Parallelism, it is hardly con- 
sistant to ignore the most important factors in the whole 
course of Evolution, on the ground that they are too complex 
to reckon with. This is the crucial error made in our problem 
to-day ; for since mind would not be mind without this variety, 
therefore all that “ mind” means in the vast region of conduct, 
and all that “conduct” means in animal evolution is centered 
in the problem of specific energies, whether Parallelism be 
accepted or not. To neglect them is the greatest practical 
error in modern Biologic Science. 
It is scarcely less wrong to read our life into simpler lives. 
This is done by most investigators of primitive fields, and 
detracts lamentably from their work. The fault originates in 
a lack of careful examination of the whole field of possibilities ; 
such an examination as we have followed out in this paper. 
So long as it is uncertain whether primitive creatures react, 
sensorily, with many responses or with one; or whether the 
forces that mould our sensory life now, are the same as gov- 
erned the analogues of our sense organs during earlier periods; 
and above all while the world’s present “ artificial, scholastic 
