It has been customary with certain authors—perhaps especially such as have interested themselves in sociological subjects—to ascribe quite a large number of man’s activities to separate instincts. Very little consideration of most of these propositions shows that they are based upon too lax a definition or a want of analysis, for most of the activities referred to special instincts prove to be derivatives of the great primal instincts which are common to or very widely distributed over the animal kingdom. Man and a very large number of all animals inherit the capacity to respond to physical need or emergency according to the demands which we classify, as the three primary instincts of self-preservation, nutrition, and {97} reproduction. If a series of animals of increasing brain power be examined, it will be found that a growth of intelligence, while it does nothing to enfeeble the instinctive impulse, modifies the appearances of it by increasing the number of modes of reaction it may use. Intelligence, that is to say, leaves its possessor no less impelled by instinct than his simpler ancestor, but endows him with the capacity to respond in a larger variety of ways. The response is now no longer directly and narrowly confined to a single path, but may follow a number of indirect and intricate ways; there is no reason, however, to suppose that the impulse is any the weaker for that. To mistake indirectness of response for enfeeblement of impulse is a fundamental error to which all inquiry into the psychology of instinct is liable. To man his big brain has given a maximal power of various response which enables him to indulge his instinctive impulses in indirect and symbolic activities to a greater extent than any other animal. It is for this reason that the instincts of man are not always obvious in his conduct and have come to be regarded by some as practically no more than vestigial. Indirect modes of response may indeed become so involved as to assume the appearance of the negation of the very instincts of which they are the expression. Thus it comes to be no paradox to say that monks and nuns, ascetics and martyrs, prove the strength of the great primary instincts their existence seems to deny.