IT S unavoidable that some lag should exist between the discovery of knowledge and its general diffusion to the various fields concerned with its application. But a prolonged lack of realization of new facts is both regrettable and uncalled for, particularly when it occurs in the various fields of human behavior, where basic principles are unearthed so slowly and so painstakingly and where their application is so vital to human problems. It seems appropriate, therefore, to call attention at this time to a fact which has lain unappreciated too long-one which carries significant implications for the understanding of a large segment of individual and social behavior. The so-called nature-nurture problem undoubtedly is far from settled, and perhaps never will be entirely a closed issue. Yet since many studies have shown so conclusively that hereditary and environmental influences are closely interrelated, the old dichotomy of nature versus nurture has tended to be discarded in modern scientific writings. The current interdependent point of view undoubtedly has led to a more unbiased and fruitful understanding of human behavior. However, after the subsistence of the somewhat recent and tempestuous controversy over the respective contributions of nature and nurture to human behavior, one fact has remained largely unappreciated: namely, that sex desire is not basically a biological an internal an a visceral a a need-or whatever other term may be employed to denote this type of humanly universal, unlearned, and recurrently compulsive behavior. That sex desire is basically a reflexive response should be obvious by now, but apparently this point is still being ignored-judging at least from what is being written in current a,nd widely employed texts in sociology, psychology, and social psychology' (let alone medical texts and popular literature). A large part of the confusion displayed in discussions of the nature-nurture problem has been occasioned simply by differences of definition. The terms instinct, drive, organic need, appetite, etc., have been employed in innumerable ways. Therefore, it is first necessary to offer a rather precise definition for this type of behavior, one which will provide an agreeable base of reference for the following discussion. The term instinct-abused and maligned as it has been-will be resurrected for present purposes. By is meant: any type of behavior which is both universal (i.e., common to all peoples at all times), and recurrently and organically compulsive. That is, it periodically affects all individuals due to factors inherent in the physiological and neurological nature of the human organism. The essential features of this definition are: first, that it eliminates learned or conditioned behavior; second, that it refers only to compulsive behavior (thus excluding reflexes); and third, that it narrows the problem down to human behavior alone (thus eliminating inferential hypotheses deducted from animal behavior). This definition does not, however, necessarily imply that instinctive behavior cannot be modified by experience or training; but it does imply that such behavior leads periodically to a painful state of organic tension which demands relief. That sex desire is not an instinct is contended simply on the basis of the definition advanced: namely, that there is no evidence (and much con-