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(1991) study of reciprocity and interchange of grooming and agonistic “sup-
port” during conflict in captive chimpanzees. Reciprocity was defined as one
act being exchanged for the same thing (grooming for grooming), whereas
interchange was defined as involving two different kinds of acts being bartered
(i.e., grooming for support). They created an actor matrix (who initiates to
whom) and a receiver matrix (who is recipient from whom) and used a corre-
lation procedure, the
K
r
test, to examine links between the two matrices while
taking account of individual variation in tendency to direct acts. They also
attempted to retain stationarity in the data by distinguishing between periods
when an alpha male was clearly established or when alpha status was in dis-
pute. Hemelrijk (1990) had shown that grooming and support were both
independently correlated with dominance rank, so whenever reciprocity or
interchange was part of a triangle of significant correlations, they partialed out
the third variable to see whether the remaining two retained significance.
Between the females, for example, a significant interchange between grooming
and support received did not depend on dominance rank. Females groomed
individuals that had supported them regardless of rank, indicating a social
bond. However, the reverse was not true in that support was not given in
return for grooming, so it was not possible to “buy” support with grooming.
Patterns of relationships were different between the sexes.
Cheney (1992) used the distribution of grooming among individuals
within a group to examine whether adversity, in the form of rivalry between
groups, had a uniting effect within the group; the expectation of this hypoth-
esis was a more egalitarian spread of grooming within the group when compe-
tition with neighbors was intense. This expectation was not upheld, perhaps
because neglected individuals would suffer a greater loss of fitness by shirking
in their support of their own group than by attempting to trade this support
for better treatment, even assuming a lack of punishment for failure to coop-
erate (Clutton-Brock and Parker 1995). Even when intergroup competition
was strong, marked hierarchies in grooming favoritism characterized intra-
group relations. This study used the distribution of grooming to generate data
with which to infer intragroup cohesion and equality. The ultimate functional
explanations given depend directly on the validity of that assumption. Our
acceptance of such hypotheses may be influenced more by our intuitive
anthropomorphic bias for their seeming correctness than by our purely objec-
tive assessment of the supporting evidence. This is the dilemma of being a
social mammal attempting to describe the societies of other mammals.
The site to which grooming is directed may have social implications.
Among long-tailed macaques (
Macaca fascicularis
), for example, low-ranking
