1897.] The Biologic Origin of Mental Variety: 3 
European drift are chipped and never polished, since though 
much evidence has been accumulated to show that man chipped 
before he polished stone in Europe, the testimony of Africa, 
Asia and America is not yet in upon such sequence in the de- 
velopment of the stone craft of primitive man. 
THE BIOLOGIC ORIGIN OF MENTAL VARIETY, OR 
HOW WE CAME TO HAVE MINDS. 
By HERBERT NICHOLS. 
Continued from Vol. XXX, p. 975). 
The widely popular theory of like nerve currents having been 
put out of the field, it remains for us to examine the rival one 
that the afferent nerve currents differ correspondingly with the 
forms of sense which they mediate. Before doing so it is well - 
for us at this point to recall the main purpose of this paper as a 
whole, and the somewhat tortuous course of its investigations 
from the beginning. Our main object, as our title states, is to dis- 
cover how man came to have such a mind as he now has; or, 
put otherwise, to discover the origin of our mental diversity and 
its relationship to our organic evolution. At the outset we 
found it doubtful whether protoplasmic life originated with 
one sense or with many. We next determined that molecular 
differences, underlying our various senses, must have been de- 
termining factors of their own selection and survival, and that 
therein, when rightly followed out, must lie the key to the 
secrets we are in search of. Alternative theories regarding 
these molecular differences then presented themselves, one of 
which we werg enabled to dispose of. And we are now left 
with the probability that the afferent nerve-currents differ 
correspondingly with the forms of sense they mediate, and 
with the task of examining what light this fact sheds on the 
origin of our minds, and on the question whether life began 
with many senses or with one. 
