[Footnote 1: The reader must be reminded that the simpler reflexes involved in the use of the heart, lungs, intestines, and all the internal organs, must be classed as part of man's native equipment. They differ from those reactions commonly classed as instincts in that they are simpler and stabler, that in their normal functioning they never rise to consciousness, and that they are almost completely beyond the individual's modification or control.]
In a general survey of this nature it IS impossible, as it is unnecessary, to examine in detail the physiological elements of the demand for food and shelter. It will suffice to point out that the first two are the ultimate biological bases of a large proportion of our economic activities. They are primary, not in the sense that they are constantly conscious motives to action, but that their fulfillment is prerequisite to the continuance of any of the other activities of the organism. Agriculture and manufacture, the complicated systems of credit and exchange which human beings have devised, are, for the most part, contrivances for the fulfillment of these fundamental demands. With the complexity of civilization new demands, of course, arise, but these fundamental necessities are still the ultimate mainsprings of economic production.
The demand for sex gratification, because of its enormous driving force and the emotional disturbances connected with it, offers a peculiarly acute instance of the difficulties brought about in the control of man's native endowment in his own best interest. While the production of offspring is its chief biological utility, satisfaction of the sex instinct itself is stimulated in human beings quite apart from considerations of the desirability or undesirability of offspring. Since the sex instinct is at once so deep-rooted and intense a driving force in human action, and its consequences of such crucial importance to both those directly involved and to the group as a whole, societies have, through law and custom and tradition, built up elaborate codes for its control. In civilized society the free operation of this instinct is checked in a thousand ways. But, as in the case of other primitive motives to action, the sex instinct, obvious as are the disasters of disease and disorganization which follow as consequences of its uncontrolled indulgence, cannot altogether be repressed.