6 PSYCHOLOGY AND PREACHING
A fact not so obvious but quite as important is that the instincts can be modified in their strength by experience. Habit which will be discussed in a later section of this chapter reinforces some and weakens others. A person born with the fear instinct dominant may, by cultivating persistently his weaker instinct of pugnacity or aggres siveness, overcome to a large extent this original handi cap. One born with the appropriating instinct in normal strength may by the formation of the proper habit very much reduce it, and develop a character of great liberality and generosity ; or magnify it until it becomes the supreme principle of conduct and so develop a character of un scrupulous covetousness. While, therefore, instincts are in a certain measure fixed, they are far from being abso lutely unchangeable factors of experience. The environ ment in which the person lives, especially the part of it which he is brought into direct relation with, acts as a selective influence, stimulating some of his instincts and developing them to greater power; and, by leaving others without stimulation, inevitably condemns them to be weak ened through atrophy. By way of application it may be remarked in passing that preaching is one method, and may be a very effective one, of bringing the person into more vital and stimulating relation with certain most important phases of his environment and thus may gradually but powerfully modify the strength of his various instincts.
Another fact of prime importance is that the instinctive organization of the human species is much less definite, fixed and rigid than that of the lower animals. The in stincts of inferior species can hardly be modified by exper ience. However, it may be done within narrow limits in the case of those which stand highest among the sub-human orders of life; but as the scale is descended this capacity becomes more limited, until finally at the lower end it reaches zero. But in man the instinctive organization is, if the crude expression may be tolerated, very much looser, and is subject to the possibility of almost indefinite modi-
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