THE MATURATION OF AGGRESSION 
I 80d 266d 
Figure 122. — Prevalence of wounds with age. The data are shown as a three-point moving average of the means. N=number 
of observations. Note that each of the periods for males is of shorter duration than for females. This indicates that 
males have a more rapid rate of maturation of aggression than do females. 
aggression during Period 4 (115 to 180 days for 
males, 150 to 245 days for females). The intervals 
approximate the ages during which each sex is 
in its prime pelage (see fig. 144 and 145). This 
Period 4 with its constant low level of aggression 
is one which I have thought of as a period of 
behavioral maturation, such that by the end of 
the sixth month for males and the eighth month 
for females the rats may be said to be fully adult 
and prepared to fully engage in courtship, mating, 
and defense of territory. 
There follows Period 5 (180 to 266 days for 
males: 245 to 368 days for females) during which 
aggression increased to a high constant level, 
which has been designated as Period 6. By the 
beginning of Period 6 each sex has just attained 
0.9 of the post-weaning increment in weight 
(Figs. 1 30 and 1 31 ). 
In the preceding paragraphs certain events asso- 
ciated with the periods of aggression were pre- 
sented, without necessarily implying any cause and 
effect relationships. There is a strong suspicion 
that these periods do have casual relationship with 
physical size. Three facts fostered this suspicion: 
(a) Males grew faster than females and likewise 
exhibited more rapid rates of increase in aggression. 
(b) The two sexes were more nearly identical in 
weight at the ages corresponding to the beginning 
of their periods, 4, 5, and 6 than they were at 
identical ages corresponding with any of these pe- 
riods for either sex. For example, the mean weight 
of females at 115 days was 250 grams and at 180 
days 346 grams. Contrast this to the data in the 
table on figure 122. These weights are for the ages 
at the beginning of periods 4 and 5 for males, and 
represent much smaller size for females than for the 
later ages (150 and 245) at which females also begin 
these two periods, (c) Table 41 shows that those 
individuals winning a conflict were generally both 
older and larger than their losing opponent. At 
least among males the loser was not only smaller 
because he was younger, but his weight was even 
190 
