The extent of the psychical accompaniments of instinctive activity in civilized man should not, therefore, be allowed to obscure the fact that the instincts are tendencies deeply ingrained in the very structure of his being. They are as necessarily inherited, as much a part of himself, and as essential a condition for the survival of himself and his race, as are the vital organs of his body. {96} Their persistence in him is established and enforced by the effects of millions of years of selection, so that it can scarcely be supposed that a few thousand years of civilized life which have been accompanied by no steady selection against any single instinct can have had any effect whatever in weakening them. The common expression that such an effect has been produced is doubtless due to the great development in civilized man of the mental accompaniments of instinctive processes. These mental phenomena surround the naked reality of the impulse with a cloud of rationalized comment and illusory explanation. The capacity which man possesses for free and rational thought in matters untainted by instinctive inclination is of course indubitable, but he has not realized that there is no obvious mental character attached to propositions having an instinctive basis which should expose them to suspicion. As a matter of fact, it is just those fundamental propositions which owe their origin to instinct which appear to the subject the most obvious, the most axiomatic, and the least liable to doubt by any one but an eccentric or a madman.