in degree in the two spheres
but not different in kind. There is no aggressive instinct or war
motive that is directed exclusively toward the outsider. Certain
tendencies toward violence and strife, modified and controlled within
the group, become unrestrained when directed toward the stranger.
Among these motives are those of sexual rivalry, fear, anger, desire,
and the play motive as an expression of any instinctive habits of
aggression that may have been phyletically established.

Since every individual creature has his needs that can be satisfied
only by preying in some way upon other animals of his own species or
others, the motives for strife are original in organic life. Every
animal lives in a world of which he is suspicious, and rightly so. He
is suspicious toward the members of his own kind and group, and toward
all strangers he shows watchfulness and fear. There are two motives,
therefore, of a highly practical nature that contribute to a general
state of unfriendliness in animal life. Both the motives of conflict
within the group, the habit of aggression and its complement, fear,
and the jealousy and display motive (the display itself probably
having originated as a show of ferocity on the part of males) must
have been transferred to relations between groups as a natural result
of the proximity of groups to one another, although this process is
not quite so simple as this would imply, since in part the outside
groups are produced by these very same antagonistic motives in the
group, for example the driving out of young males because of sexual
jealousy. The presence of other groups must have excited all the
motives of warfare at a very early stage, and this contrast had the
effect of stimulating the social feeling of the group and developing
control of impulses on the part of individuals within the group toward
one another. So the motives of combat, as shown within the group and
toward outsiders, developed, so to speak, by a dialectic process.

Fear and the predatory impulse, the sexual and display motive, play or
the hunting activity as a pleasure for its own sake, with a desire
perhaps to practice deception and to exercise intelligence, presumably
introduced some kind and degree of definite warfare among primitive
groups of men at a very early stage of human life, although of course
such a conclusion can be only speculative. Increasing intelligence,
the power of discriminating and of reacting to secondary