Table 55. — Colony k: Passage 3 Burrow and East 
Alley ladder , April-May 1949* 
Rat’s 
Number 
Place of 
birth 
Maturity 
index 
May 
weight 
May 
wounds 
Males: 
79 
SAB 
1.42 
392 
35 
685 
SAB 
1 1. 00 
360 
24 
868 
NAB 
11.25 
488 
26 
97 
Area I 
1.90 
504 
26 
873 
Area I 
III. 00 
374 
4 
670 
Area II ... . 
1.67 
450 
27 
54 
Area III . . . 
1.67 
462 
20 
56 
Area III . . . 
11.50 
444 
39 
57 
Area III . . . 
II. 00 
342 
3 
657 
Area III . . . 
1.50 
452 
27 
662 
Area III . . . 
1.57 
450 
14 
83 
NAB 
II. 00 
477 
17 
742 
Area IV. . . 
11.25 
414 
3 
Mean . . 
1.98 
429 
20. 4 
♦No females. 
J. Stress and Reproduction. The accounts of indi- 
vidual colonies amply document the reality of an 
intercolony gradation of characteristics. Even so 
an appreciation of the consistency across charac- 
teristics is difficult from these general accounts. I, 
therefore, arbitrarily divided the colonies into 
three groups (figure 128) which may be considered 
as having high, medium, or low social rank. These 
rankings reflect what I prefer to call social class 
(see pps. 176 to 178, 255 to 259, and 280 to 
281). 
Relevant characteristics of these three social 
classes are presented in table 56. Each of the 130 
rats in this analysis was between 8 and 14 months 
of age. The higher ranked class contains pro- 
portionately the most females; they were larger; 
had grown faster; had conceived more often; reared 
proportionately more of the young conceived; and 
were less frequently wounded in combat. Medium 
ranked or middle class rats exhibited less favorable 
status on each of these six characteristics. Similarly 
on each characteristic the lowest ranked rats fared 
even less well than did the middle class rats. In a 
general way we are justified in concluding that 
the less favorable are these six characteristics 
the more intense has been the socially stressful 
experience of the rats forming the class. 
Yet, social class is far from as discrete a phenom- 
enon as table 56 seems to indicate. Had we con- 
sidered a less closed population than that in the 
Towson enclosure, I am sure that nearly impercep- 
tible differences would characterize any particular 
ranked colony in comparison with the next lower 
ranked colony. 
In order to gain more precise insight into the 
gradual transition in rank among colonies, five 
variables for each colony were transformed into 
indices. Each might vary from one to zero or near 
zero (table 57). The lower the index the greater 
had been the intensity of associated stressful 
conditions. 
1. Weight index=l-(M-W / j M-m) 
Where: 
M— Maximum mean weight for a single of the 
11 colonies. 
m= Minimum mean weight for a single of the 
11 colonies. 
fff=Mean weight of the particular colony for 
which the index is being calculated. 
This index was calculated separately for each 
sex and half their sum is shown in the first column 
of table 57. Because of the importance of the sex 
ratio to stress a value of 1.0 was arbitrarily given 
for males in colonies lacking males, and 0.0 for 
females in colonies lacking females. Colonies 
whose weight index approached 1.0 had experi- 
enced few of the stresses which inhibit growth, 
whereas colonies whose weight index approached 
zero had experienced many stresses. 
2. Proportion of the colony which were females. 
The more females in a colony outnumber males 
the less stress the colony has experienced. This is 
discussed in detail under the topic of sexual 
behavior (pp. 152 to 158). 
3. Homogeneity index. 
The members of a colony may have been born 
mostly in the same locality. If this is so, the group 
has marked homogeneity of origin and similarity 
of social experience. On the other hand, the 
members of a colony may have had several 
different places of origin. Such colonies have 
little homogeneity of origin and experience 
considerable stress as a result of their lack of 
common social history. Let 0, ... 0 n be the 
places of origin of the members of a colony in an 
order of decreasing number of individuals per 
place of origin. Let n x . . . n n be the number of 
individuals from origin 0[ . . . 0„. Then the 
homogeneity index=[(l X«i)+ (O-SX^) - ! - (0.25X 
« 3 ) . . . n„]/N. TV represents the number of individ- 
uals in the colony. By this arbitrary method a 
high homogeneity of origin approaches 1.0 and a 
214 
