A fairly satisfactory definition of instinct is that supplied by Dr. and Mrs. Peckham in the course of their study On the Instincts and Habits of Solitary Wasps.  “Under the term ‘instinct,’” they say, “we place all complex acts which are performed previous to experience and in a similar manner by all members of the same sex and race, leaving out as non-essential, at this time, the question of whether they are or are not accompanied by consciousness.”  This definition is quoted with approval by Lloyd Morgan, who modifies and further elaborates it (Animal Behavior, 1900, p. 21).  “The distinction between instinctive and reflex behavior,” he remarks, “turns in large degree on their relative complexity,” and instinctive behavior, he concludes, may be said to comprise “those complex groups of co-ordinated acts which are, on their first occurrence, independent of experience; which tend to the well-being of the individual and the preservation of the race; which are due to the co-operation of external and internal stimuli; which are similarly performed by all the members of the same more or less restricted group of animals; but which are subject to variation, and to subsequent modification under the guidance of experience.”  Such a definition clearly justifies us in speaking of a “sexual instinct.”  It may be added that the various questions involved in the definition of the sexual instinct have been fully discussed by Moll in the early sections of his Untersuchungen ueber die Libido Sexualis.

Of recent years there has been a tendency to avoid the use of the term “instinct,” or, at all events, to refrain from attaching any serious scientific sense to it.  Loeb’s influence has especially given force to this tendency.  Thus, while Pieron, in an interesting discussion of the question ("Les Problemes Actuels de l’Instinct,” Revue Philosophique, Oct., 1908), thinks it would still be convenient to retain the term, giving it a philosophical meaning, Georges Bohn, who devotes a chapter to the notion of instinct (La Naissance de l’Intelligence, 1909), is strongly in favor of eliminating the word, as being merely a legacy of medieval theologians and metaphysicians, serving to conceal our ignorance or our lack of exact analysis.

It may be said that the whole of the task undertaken in these Studies is really an attempt to analyze what is commonly called the sexual instinct.  In order to grasp it we have to break it up into its component parts.  Lloyd Morgan has pointed out that the components of an instinct may be regarded as four:  first, the internal messages giving rise to the impulse; secondly, the external stimuli which co-operate with the impulse to affect the nervous centers; thirdly, the active response due to the co-ordinate outgoing discharges; and, fourthly, the message from the organs concerned in the behavior by which the central nervous system is further affected.[1]