Appearance and Inheritance of Instincts 201 
probable that it will be formed often again in the same 
individual, and this repetition will produce a constantly 
increasing, corresponding modification of the nervous 
tissue in the individual concerned, which will be repro- 
duced in his descendants. A new association of ideas 
can arise and actually does arise independently, within 
certain limits, of the nervous structure of the individual, 
and therefore independently of the germ substance also 
which has produced this latter, in so far as the fortu- 
itous external circumstances which produce this new 
association exert a strong and overmastering influence: 
Among a thousand individuals, quite identical in regard 
to the structure of their nervous mechanism, this new 
association of ideas will be developed in only one, on 
account of the special external circumstances in which 
it happens to be placed. 
But without the inheritance of acquired characters 
this fortunate new association of ideas, and the repeated 
employment of it by the individual later, would be com- 
pletely lost for the species. To assure its transmission 
from one generation to another there would remain only 
imitation or education in the widest sense of the word. 
But the fact is that nearly all the instincts are, on the 
contrary, truly inborn, that is to say they are produced 
without any psychic educative influence whatever. 
It is clear also that not all the members of the older 
species will be able to make use of a new, fortuitously 
developed instinct through educative imitation and later 
through heredity, but only the immediate descendants or 
associates of the individual in whom it was developed. 
All other members of the species would be excluded. 
And so those will be the only ones, who, in consequence 
of this newly adopted habit, will make a thorough 
