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.

It is generally recognized that in men and animals alike the sex
impulse is apt to manifest itself in very vigorous and sustained
efforts toward its natural end; and that in ourselves it may
determine very strong desires, in the control of which all the organized
forces of the developed personality, all our moral sentiments and
ideals, and all the restraining influences of religion, law, custom
and convention too often are confronted with a task beyond their
strength.[1]

[Footnote 1: McDougall: _Social Psychology_, 11th ed., pp. 399-400.]

There is considerable agreement among students of the
subject that the emotional energies aroused in connection
with the sex instinct may be drained off into other channels,
and serve to quicken and sustain both artistic creation and
appreciation and social and religious enthusiasms of various
kinds. And the sex instinct, as we shall find in our discussion
of Racial Continuity (see p. 243) is the basis of the family.

PHYSICAL ACTIVITY. The difference between sticks and stones
and living beings consists primarily in the fact that the latter
are positively active; the former are passively acted upon.
The stone will stay put, unless moved by some external agent,
but even the amoeba will do something to its environment.
It will stretch out pseudopodia to reach solid objects to which
to cling; it will attempt to return to these objects when dislodged;
it will actively absorb food. Higher up in the animal
scale, "Rats run about, smell, dig, or gnaw, without real reference
to the business in hand. In the same way Jack (a dog)
scrabbles and jumps, the kitten wanders a