D. The Role of Aggressive Behavior in Social Organi- 
zation. Social organization among rats has its 
primary expression in the close association of 
several individuals in the same burrow or in a 
group of neighboring burrows. All types of inter- 
actions between individuals which foster the forma- 
tion or maintenance of such a group comprise 
facets of the social organization. These include 
(1) maternal care, (2) contacts among juveniles 
living in the same locality, (3) assembly in winter 
for the purpose of conserving body heat, and (4) 
aggressive behavior which maintains exclusion of 
nonmembers. A number of other conditions 
facilitate the molding of the population into local 
groups. They include (1) attachment to place of 
birth, (2) similarity of past history, (3) presence of 
barriers to locomotion, and (4) attraction to a 
common goal. 
The members of a group frequently engaged in 
similar activities at about the same time and place, 
but there was no evidence of rats engaging in co- 
operative behavior of the kind requiring joint effort 
to accomplish a task incapable of attainment by a 
single rat just taking a longer time. Even so, 
aggressive behavior, whether actual or threatened, 
frequently lead to the formation of more closely 
knit groups. The following description of aggres- 
sive behaviors, and the conditions under which 
they were expressed, will delineate the role of 
aggressive behavior in social organization. 
a. Nose-touching. The behavior of nose-touching, 
of itself, is not an aggressive behavior. It merely 
involves two individuals approaching to the point 
that the tips of their noses actually or apparently 
come in contact. This is an act of recognition 
which is by far the most common interaction. It 
becomes an aggressive interaction to the extent 
that one of the participants interprets the recogni- 
tion as portending a threat. Most frequently each 
rat proceeds with its prior course of action following 
the nose-touching. Occasionally some positive 
interaction such as sexual behavior develops. On 
the other hand one of the members may immediately 
and rapidly flee even though the other member of 
the pair does not pursue it. This reaction has been 
interpreted as indicating a more subordinate 
status for the rat which flees. More infrequently 
both individuals run in opposite directions follow- 
ing nose-touching. 
b. Avoidance behavior. By avoidance behavior is 
meant the change in the route toward a goal or the 
departure from a goal upon perceiving another rat. 
The term avoidance behavior will also be used to 
include similar actions by one rat in the absence of 
any other rat but at a place where frequent inter- 
actions with other rats have previously occurred. 
There are two circumstances, at least one of which 
always operates, in the avoidance of one rat by 
another. The first of these is that there shall have 
been a marked difference is social rank previously 
established. When such a differential exists the 
subordinate rat runs aside or away from its domi- 
nate associate, whenever and wherever they en- 
counter. Even when the subordinate rat detects 
its dominate associate, when the latter is not aware 
of the former’s presence, the subordinate rat will 
turn and run away. This raises the question: Can 
one rat detect the identity of another at a distance? 
The only sure statement that can be made is that a 
subordinate rat can recognize the social rank of 
another at distances of 10 to 20 feet during the dawn 
and dusk hours. The avoidance may occur whether 
the dominant rat is facing toward or away from the 
subordinate one. Even though it may be true that 
there is no recognition of individual rats as individ- 
uals, there are actions or postures characteristic 
of extremes of social rank that identify them as such. 
The major aspects of these socially differentiating 
behaviors will be mentioned here. The dominant 
rat more frequently stops at those intersections of 
paths or passages through fences where they are 
likely to be perceived or encountered by other rats. 
Here they groom or pace back and forth. In con- 
trast to this the stopping of more subordinate rats 
at such points is one of momentary hesitation, while 
they look and listen before proceeding on in a 
hurried fashion. There is also the wheeling around 
by the dominant rat to face the approaching sub- 
ordinate rat, but in so turning it does not give 
ground. Upon a continued approach by the sub- 
ordinate rat the dominant one then begins a 
deliberate prance toward it. This prance is one of 
body raised by extending the limbs, while at the 
same time raising high the forepaws during the 
forward steps. If the subordinate rat flees soon 
enough, the dominant one may not give chase. 
When the dominant rat, which has been detected 
by the subordinate one, is located along the route 
between the goal which the subordinate has left 
and the one toward which it is proceeding, there is 
elicited a peculiar vacillating movement charac- 
terized by an alternation of approaches toward and 
withdrawal from the dominant rat. This may also 
take the form of movements back and forth in an 
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