176 INTELLIGENT BEHAVIOUR 
of efficiency—heredity and use. Just as the heart and lungs 
must inherit the power of standing abnormal strain if the 
animal is to avoid elimination in times of unwonted exertion, 
so must the nervous system inherit some reserve power of 
dealing effectively with unwonted circumstances by intelligent 
accommodation, if the animal is not to fall a victim to such 
circumstances. In other words, at times of heightened com- 
petition those animals which can draw on a reserve fund of 
intelligent accommodation will survive, while the stupid 
blunderers will be eliminated. We may term this reserve 
fund of intelligent accommodation, this inherited ability to 
meet specially difficult circumstances as they arise, inate 
capacity. From the nature of the case it must be indefinite, 
for it must carry with it the ability to meet unforeseen 
combinations of the environing forces by new combinations 
of the results of experience. Its distinguishing mark is 
plasticity, in contradistinction to the stereotyped fixity of 
typical instinct. And accompanying its evolution there is 
probably, as we have seen, a dissolution of its antithesis, 
instinct. Thus may we account for the fact that man, with 
his great store of innate capacity, has so small a number of 
stereotyped instincts. 
But the dissolution of instincts is not complete. Residua 
are left in the inherited mental constitution. And these we 
term congenital tendencies and propensities. They differ from 
the typical instincts in the fact that the definiteness of response 
has been lost. They dictate a general trend of action, but 
the particular application in behaviour is due to intelligent 
accommodation. They are commonly spoken of as instinctive ; 
and their mode of origin justifies the use of the adjective in 
association with the term “propensities.” But it must be 
remembered that the behaviour to which they lead is not, as 
such, wholly instinctive ; it is a joint product of instinct and 
intelligence, the general trend being due to the instinctive 
propensity, while the mode of application is guided by 
intelligence. 
There is, however, another way in which analogous 
