various kinds of dispositions, but are in greater or less degree the
common property of us all.

There flows through the life of every creature a steady stream of
energy. Scientists have not been able to decide on a descriptive term
for this all-important life-force. It has been variously called
"libido," "vital impulse" or "élan vital," "the spirit of life,"
"hormé," and "creative energy." The chief business of this life-force
seems to be the preservation and development of the individual and the
preservation and development of the race. In the service of these two
needs have grown up these habit-reactions which we call instincts. The
first ten of our list belong under the heading of self-preservation
and the last two under that of race-preservation. As hunger is the
most urgent representative of the self-preservative group, and as
reproduction and parental care make up the race-preservative group,
some scientists refer all impulses to the two great instincts of
nutrition and sex, using these words in the widest sense. However, it
will be useful for our purpose to follow McDougall's classification
and to examine individually the various tendencies of the two groups.

=In Debt to Our Ancestors.= An instinct is the result of the
experience of the race, laid in brain and nerve-cells ready for use.
It is a gift from our ancestors, an inheritance from the education of
the age-long line of beings who have gone before. In the struggle for
existence, it has been necessary for the members of the race to feed
themselves, to run away from danger, to fight, to herd together, to
reproduce themselves, to care for their young, and to do various other
things which make for the well-being or preservation of the race. The
individuals that did these things at the right time survived and
passed on to their offspring an inherited tendency to this kind of