I do not believe it is possible to completely 
separate cause and effect for most of these criteria 
for judging social rank. For example, an animal 
may have a slow growth rate and a low adult 
weight as a result of intense competition from other 
juveniles or from frequently receiving psychological 
drubbings from adults while it was a juvenile, then 
because of its small size as an adult it will more 
frequently lose in combats and thus exhibit a low 
priority of action with reference to reaching and 
satisfactorily responding with goals. In other 
words, as a result of developing low social rank, 
a rat grows slowiy, and then, because it is small, as 
an adult it is unable to develop higher social rank. 
Likewise, a rat may develop low social rank be- 
cause it lives far from the food source, and because 
it has developed low social rank it is unable to 
shift its place of residence to a more favorable 
situation nearer the source of food. The social 
structure of a society of rats develops through the 
interaction of several variables such that cause and 
effect of rank within the structure are inextricably 
interwoven. Furthermore, the relative effect of 
any one variable changes with time. When these 
circumstances are recognized, it is possible to take 
the facts at hand and assign relative social rank for 
any particular time in the history of the population. 
C. Culture. Through time the physical struc- 
ture of the environment is modified by the rats 
w hich inhabit it. Much of this modification, such 
as the pattern of trails or the presence and position 
of burrows, alters the way of life of later generations. 
Through time the social structure of the population 
changes. These changes modify the social struc- 
ture of later generations, and in a general way 
predetermines the fate of particular individuals. 
The characteristics which describe the rats’ 
society at any particular time can largely be 
described in quantitative terms, or in terms of 
rates of change. They include: (1) growth of 
trail way communications systems (pp. 54 to 63); 
(2) growth and disintegration of burrow (pp. 15 to 
54); (3) denuding of vegetation; (4) density of the 
population (pp. 244 to 246); (5) individual rates 
of growth (pp. 216 to 236); (6) mortality (pp. 
237 to 244); (7) reproduction (pp. 214 to 216); 
(8) migration (pp. 170 to 171, 214); (9) group 
structure (i.e. : sex ratio (tables 56 and 57); 
places of birth (pp. 196 to 198); dominance of 
members in combative situations (pp. 179 to 
195) etc.). One may designate these character- 
istics at any time as representing the state of the 
culture of the group. 
This raises the question of levels of these states 
with reference to desirable or undesirable states of 
the culture. Two criteria may be taken forjudging 
the level of culture. In the direction of higher 
levels these criteria are: 1. The characteristics per- 
taining to the group or its component members 
should enable them to compete more effectively 
when they come in contact with members of other 
groups. 2. The cultural state should permit the 
most efficient utilization of available energy sup- 
plies compatible with maintaining a stable popu- 
lation density. Thus, I consider the levels of 
culture existing through time as having much of the 
same type of variation as does social class among the 
local colonies of a population during a particular 
time of its history. Social class and cultural level 
refers to the standard of living; that is to the ease of 
satisfying the needs felt by the individual. Thus, 
the average individual in a group having high 
social class or the average individual of a popula- 
tion having a high level of culture, will, in either 
case, have a high standard of living. 
One can judge social rank and cultural level, as 
I have defined them by two specific conditions: 
1. Growth rate of the individual with respect to 
the attainment of its genetically determined maxi- 
mum weight or size. 2. Reproductive success. By 
this latter I mean that conceptions attempted will 
be effected, and that the progeny conceived will be 
born and reared to weaning. 
All other characteristics by which social rank or 
cultural level may be assigned should be either 
causative or dependent variables to these two or 
should arise from the same set of independent 
variables. By so phrasing sociality and culture, 
these manifestations of life may be treated from a 
comparative biological viewpoint. 
Reproductive success was defined in the above- 
limited sense, since it is quite obvious that the repro- 
ductive potential of any species in the absence of 
limiting factors will permit the population to 
increase in numbers beyond the available energy 
supplies to support them. A very rapid rate of 
increase in density may indicate relatively high 
social class for the groups composing the popula- 
tion, but this criterion cannot be used to indicate 
a high cultural level, unless the system embodies 
some method whereby density will be checked at a 
level compatible with available energy sources, 
without reducing the individual growth rate. 
178 
