3
Patterns and Functions of Grooming Behavior
among the Common Indian Langur Monkey
James J. McKenna
For many primate species grooming is a predomin-
ant and socially important behavior pattern diverse
both in the form it can take and the social situations
within which it is initiated. While not the only behavior
that often cuts across different age and sex classes to
promote cohesion, the tremendous amount of time
and energy invested by some species in this activity
suggests that as a bond-building mechanism social
grooming has played an auxiliary if not complemen-
tary role in the evolution of primate sociality.
Among primates social grooming is thought by in-
vestigators to provide useful information on many dif-
ferent aspects of group life. Grooming data has been
used to measure developmental processes in the
mother-infant relationship (Hinde 1974, Kaufman
and Rosenblum 1969), to document the growing net-
work of attachments and subgroup formations within
and among different primate groups (Simonds 1973,
1974; Furuya 1957; Kummer 1968), and as an exam-
ple of parental investment (Trivers 1974, Hrdy 1976).
While Sade (1965) and Lindberg (1973) demonstrated
how grooming patterns reinforce social relationships
and, in some cases, regulate behavior, Chance and
Jolly (1970) suggested that within private societies the
direction of grooming can be used as one criterion to
delineate "attention structures" and to assess the de-
gree of social centrality of leader individuals around
which others are organized. More recently, Boese
(1976) used data collected on preferred grooming
clusters to propose that West African baboons (Papio
papio) exhibit harem units based upon sexual but not
social exclusivity.
Although an impressive number of works dealing
primarily with the social functions of grooming exist,
there is not unanimous agreement that grooming be-
havior has been interpreted and dealt with correctly,
nor that its function has been entirely understood.
Alexander (1974) argues that not enough attention
has been given to the disease-controlling functions of
grooming, particularly since grooming may have orig-
inally functioned only as a parasite-controlling
mechanism and not as an accomodation to group liv-
ing. To varying degrees Alexander's position receives
support from Hutchins and Barash (1976) and Free-
land (1976) who strongly argue that a much closer look
at the relationship between disease pressures and so-
cial behavior is warranted.
This paper examines the forms, the contexts, and
the functions of social grooming behavior among the
common Indian langur money (Presbytis entellus).
These data suggest, particularly with respect to the
question of functions, that while grooming no doubt
serves both social and hygienic functions, it does so in a
context apparently dictated -by social needs. It is con-
cluded that social grooming among langur monkeys is
highly integrated into almost all aspects of group life
and, while not a reliable behavioral index to status
differentials between group members, it is important
in assessing role complexes.
Materials and Methods
The study group was housed in a dome-shaped
mesh enclosure approximately 35 feet high by 45 feet
in diameter. Starting from the enclosure floor six dif-
ferent levels of sitting bars and platforms, interspersed
every three to five feet, allowed proper social and
spatial refuge. An L-shaped mesh partition support-
ing plywood sitting platforms was situated in the
center of the enclosure.
According to Jay's (1965) field data, the population
structure included an adult male (about ten years of
age with extracted canines and musculature fully de-
veloped); eight adult females (all at least silx years of
age, primiparous or multiparous); four immature
juvenile females (all between the ages of two and four
years of age); four immaturejuvenile males (with mus-
culature not fully developed and incompletely
erupted canines); and, finally, two dependent infants
less than eight months old.
To collect data on the form, frequencies, and dura-
tions of behavioral patterns for group members three
different sampling techniques were utilized: focal be-
havior samples, focal animal samples, and behavior
spot checks. A focal behavior sample involved a fifteen
minute observation period wherein all grooming ac-
tivities were recorded and notation was made of which
animal initiated the grooming interaction, which other
animal received it, its context, and what part of the
anatomy was groomed. During a focal animal sample
all behavior exhibited by and toward one individual
(the focal animal) during a fifteen minute observation
period was recorded. The duration of the behavior,
the actor, the receiver and the participants were noted.
Behavior spot checks involved a random scan and
periodic survey of the momentary activities of each
individual at the time of observation (see Altmann
1974). Combining the three sampling procedures a
total of 1500 observation hours were completed.
Tabulation of the data followed the procedure used
by Lindberg (1973), in which a grooming bout was
considered to be any paired occurrence of grooming
involving a recognizable actor and receiver not inter-
rupted by a third animal or by a major relocation of
one of the participants. Reciprocal grooming (animal
A grooms B, then, animal B grooms A) was considered
as two different bouts. If three or more animals
groomed simultaneously (animal A grooms animal B
while animal C grooms A), each grooming dyad was
scored separately. If more than ten seconds passed
between bouts, or it a grooming sequence was termi-
nated but begun again after an individual invited a
partner to resume grooming, then this was scored as a
second grooming bout even though the participants
had previously groomed during the sampling period.
Forms of Grooming
Although the contexts were varied, three types of
grooming were recognized for captive Hanuman lan-
gurs: 1) relaxed social grooming, 2) tension-reducing
grooming, and 3) self-grooming (see table 1). Groom-
ing interactions involving more than one animal and
not accompanied by aggressive or tense vocalizations,
postures, and/or facial expressions (grimaces) were
scored as bouts of relaxed social grooming. In contrast,
any bout preceded by an embrace, a social present,
aggressive behavior, a social or sexual mount, or a
sexual solicitation involving tense vocalizations and/or
facial expressions was scored as a tension-reducing
groom. Finally, self-grooming was scored when an in-
dividual licked or picked through its own skin, hair, or
teeth.
Table 1. Taxonomy of the forms, contexts, and percentages of
different grooming behaviors observed among captive Hanuman
langurs (P. entellus)
As Table 1 reveals, of the observed 1907 initiated
grooming behaviors 60% involved relaxed social
grooming, 35% involved tension-reducing grooming,
and 4% involved solitary or self-grooming. Utilizing
Sparks (1967) distinctions, I computed that, of the
60% (n= 1146) classified as relaxed social grooming,
4% took the form of mutual grooming (animal A and B
groom each other simultaneously); 53% involved
allo-grooming (animal A grooms animal B); 42% in-
volved reciprocal grooming (animal A grooms animal
B, then, animal B grooms animal A); and, finally, in
less than 1% of the relaxed social grooming total the
form of grooming was unclear, since observation
began after the animals had initiated the interaction.
Aggressive behavior preceded 63% of tension-
reducing grooming bouts (667 or 35% of all social
grooming bouts observed). Ventral-ventral embracing
was the second most frequent behavior to precede
tension-reducing grooming with 22% of the total.
Sexual solicitations, social mountings, and social pre-
senting were roughly equal in eliciting grooming re-
sponses (2.5%, 1%, and 4.2% respectively).
The third and least frequently observed form of
grooming among captive langurs was self-grooming.
This form of solitary skin care occurred in 4% of the
total number of grooming behaviors observed. Al-
though spatial and, therefore, social isolation often
preceded self-grooming, it was certainly not the only
condition in which it was initiated. Self-grooming
often occurred between reciprocal grooming sessions
and/or following or preceding allo-grooming by either
one of the participants.
Frequency and Distribution of Grooming Patterns
by Age and Sex Class
Figure 1 shows the percentages by which age and sex
classes acted and received social grooming (relaxed
and tension-reducing grooming combined). Based
upon 94 fifteen-minute samples on each of the adults
and immatures (excluding the neonates) and 399 focal
behavior hours (1,596 fifteen-minutes observation
periods) I found that during any one sample period an
average of 3.6 individuals could be found either as
actors or receivers in grooming interactions. The adult
male was involved in more grooming interactions than
any other individual (331 or 10% of the total and
received approximately twice as much grooming as he
returned.
As an age and sex class the adult females partici-
pated in the actor role more than twice as frequently as
they did in the receiver role (actor to receiver ratio for
adult females was 1/2.2). While a t-test comparing the
differences between the mean frequency of initiated
grooming bouts per animal per class showed that adult
females initiated and acted grooming at rates signific-
antly different (p. <01) than either immature males or
females, there is much variation within age and sex
classes which deserves attention. When adult females
are treated as a class of individuals grouped on the
basis of age and sex statuses the standard deviation was
46 and the coefficient of variation was extremely high
(21.3). This figure assumes more meaning when it is
considered that one adult female (Goldie) initiated far
4
Grooming Behavior
SOCIAL (96%)           SELF (4%)
RELAXED (60%) TENSION-REDUCING (35%) ____
la   0 _
-  0q      a  a<aaa,
A                0~~~j
a  q
a-
*H
60
0 60
0
;  50
0
".~4
cd 40
0
Xl 30
ew
t  20
8 10
C.)
Ad'   A??
I S4
Acts Groom
Receives Groom
Figure 1. Percentage contribution by age and sex class
to acting and receiving social grooming.
less grooming than any of the immature females and
far less than one of the immature males, who topped
her grooming scores by over 58 initiated grooming
bouts. This kind of individual variation holds true for
comparisons between other individuals of different
age and sex classes as well. Therefore, it is important to
realize that general interclass distinctions are often
different from the behavioral records of individuals.
Age and sex class membership promotes relative but
not absolute interclass differences.
Duration versus Frequency of Grooming
Although frequency counts reveal what behaviors
are more likely to be exhibited by members of various
subgroups of the society, the figures, if taken alone,
are inadequate or, worse, misleading. For example,
the data reveal that quantitative differences of groom-
ing interactions are sometimes less than dramatic (e.g.
the adult male compared with some of the adult
females); however, by examining the quality of groom-
ing as defined by the length of time one animal actually
grooms another, more meaningful differences ap-
pear. Here an extreme example can be made between
the adult females and the adult male. As described
previously, the adult male was involved in over 10% of
the observed social grooming and during these in-
teractions he was the recipient far more frequently
than he was the actor. The grooming data are even
more skewed in favor of the adult male when the
duration of his grooming activities is considered.
While the mean duration of social grooming by the
adult females of the adult male is 4.6 minutes, the
mean duration of his reciprocal grooming of the adult
females was only 23 seconds (as timed by a stop watch).
In general, both the frequency and quality (as defined
by duration) of social grooming initiated by adult and
immature females is substantially different from that
exhibited by males. While females invest a great deal of
time in grooming, males invest little and receive much
(see Figure 2).
Not only did adult females initiate social grooming
more frequently and for longer periods of time, but
their grooming networks were much more extensive.
Inasmuch as 37% of their grooming was directed to-
ward the immature males and females and 23% to-
ward the adult male, the adult females clearly directed
grooming across age and sex classes in opposite social
directions. Particularly for the immature males, the
social grooming by the adult females seemed to have
an integrating effect. Because the adult male main-
tained exclusive sexual (copulatory) rights to the adult
females, the immature males as potential sexual com-
petitors had ambiguous and precarious social posi-
tions. However, the adult male threatened the imma-
ture males only when they were sexually solicited by
adult females but not when they were groomed by
them. Whatever peripheralizing effect the adult male
may have had on the immature males, these socio-
sexual proscriptions appeared counteracted by the
grooming activities initiated by the adult females.
Without disruption to the society, the immature males
were drawn into the social nucleus of the group to
establish tactile relationships with adult females.
0
0
~ 5
00
U 1
? w
Q C l ) 32
HZ~:
I
I V?
I d'
mean
median
Figure 2. Mean and median duration of initiated social
grooming per animal per class.
Grooming Invitations and Methods
The most common social grooming solicitation oc-
curred in relaxed social settings and was scored when
an actor, moving into proximity of another (within 12
inches), attempted either by watching or hand man-
ipulation to establish visual or passive tactile contact
with a potential groomer. After succeeding and while
in close proximity, the actor stretched its ventrum usu-
ally in front of the receiver and while scratching its own
ventrum, the actor (inviter) looked away. Although
over 33% of the relaxed social grooming bouts were
preceded by such a grooming solicitation, there were
many variations of this sequence. Occasionally, an
actor established eye contact but then immediately
5
a
I
I
looked away from the receiver while scratching its
ventrum or an actor stretched and presented its ven-
trum without scratching. An alternative grooming in-
vitation was leaning forward in front of a potential
groomer, sometimes establishing tactile contact, or
lying stretched out on the belly (ventrally) either di-
rectly in front of the receiver or lying over part of the
receiver's body, such as a leg. The draping of an arm
over another animal while simultaneously avoiding
eye contact could also elicit social grooming bouts and
preceded 6% of them. In many instances of social
grooming no invitation was apparent. However, with
respect to social grooming bouts in which no grooming
invitation was observed (23%), the groomer often had
approached the receiver from a different area of the
enclosure. It might be that in these contexts grooming
acted as an appeasment mechanism that allowed an
animal to relocate socially with respect to another by
reducing the possibility that its presence would elicit an
aggressive response.
With respect to tension-reducing grooming it is ex-
ceedingly difficult to discuss what constitutes an invita-
tion because in only 3.8% of such bouts was there a
grooming solicitation performed in the manner de-
scribed above. Reference to context is essential because
tension-reducing grooming is fundamentally a part of
a series of behavioral events in which either the
groomer or groomee has been involved. Tension-
reducing grooming typically followed aggression, a
social or sexual mount, presenting, and/or ventral-
ventral embracing (Table 1). It may be interspersed
between any sequence of these behavior patterns or
any combination of them.
After approaching and tagging the adult male in a
sequence interpreted as a confirmation of their age
and sex class roles with respect to each other, a young
immature male may immediately run to a peer group
member and, while vocalizing and grimacing, be
groomed by him. Alternatively, the peer group
member might mount him first, then, groom him.
It is not always the receiver of aggression that does
the grooming. Following an embrace with an aggres-
sor the recipient of the aggression may turn away and,
while grunting and grimacing, be groomed by him.
These behavioral sequences suggest the possibility that
in such contexts the mount, the embrace and similar
actions communicate a desire to be groomed (possibly
for reassurance). Tension and conflict situations which
vary greatly in their intensities and form clearly com-
plicate the discussion of grooming invitations and their
functions. Indeed, the possibility exists that particular
behaviors such as grooming have multiple functions
and, depending upon the specific situation and the
specific individuals, multiple meanings. In one context
the recipient of aggression may groom to appease the
aggressor and to prevent the aggression from continu-
ing while in another context the aggressor may groom
the victim, thereby reassuring the recipient that ag-
gression has ceased and that non-aggressive behaviors
may be resumed between them.
The Relationship Between Grooming and Aggression
To better assesss the functional relationship bet-
ween grooming and aggression among captive langur
monkeys, a correlation coefficient which measures the
degree or extent of a linear relationship between the
two behaviors was computed. By using 500 fifteen-
minute focal behavior samples for aggression and 500
fifteen-minute focal behavior samples for grooming,
the proportion of times each individual received ag-
gression and acted in grooming was determined first.
After computing paired scores for each animal in the
group (X=proportion of times animal A received ag-
gression, and Y=proportion of times animal A acted
grooming) I entered the data into a Pearson-r correla-
tion matrix. The resulting (r) was interpreted in the
following way: if (r) was negative, it indicated that as
grooming increased aggression received decreased
and vice-versa; if (r) was 0, no linear relationship
existed between the two behaviors; and, finally, if (r)
was positive, grooming increased as aggression in-
creased and vice-versa. Testing to determine if the (r)
value was significant (p. <.01), a t-value was deter-
mined and compared with the tabular (t) value with
n-2 degrees of freedom.
The correlation proved positive (r= +4.68 with a
t=2.94). In other words, within the specified confi-
dence intervals it can be expected that when grooming
increases between individuals so will aggression. It is
interesting to find that, if taken at face value, the
commonly held assumption that grooming solidifies
relationships, strengthens social bonds and, as a result,
decreases the amount of aggression directed toward
those who perform it, has proved questionable. Yet,
especially in this instance interpreting a cause-and-
effect relationship is extremely risky. Clearly, the
statistics reveal the importance of considering not sim-
ply the numbers, but considering the contexts from
which the numbers were obtained. The question to be
asked is the following. In light of the statistics, which
suggest otherwise, can it still be assumed that among
the common hanuman langur grooming has a positive,
or tension-reducing effect on the group at large?
One must consider several factors. The form of ag-
gression directed by individuals is not made explicit by
the correlation. Most aggression was neither tactile nor
serious but instead it involved facial, bounce, or hand
threats. So too, aggression was often directed in a
positive way as, for example, to stop others from fight-
ing, to quell factionalism, and to protect infants from
inept substitute caretakers. The adult females per-
formed most of these aggressive policing roles, and
since they also were involved in more grooming in-
teractions than any other age and sex class the chances
were increased that grooming and aggressive scores
would compute linearly. But the most important part
6
of the question remains, and that is whether grooming
behavior is a mechanism that can promote peace by
reducing aggressive levels. It is here that an analysis of
context shows that in over half of all the aggressive
interactions (both tactile and nontactile), grooming
immediately followed and was initiated by the receiver
of that aggression. That social grooming functions not
only to promote bonds and relationships, but also to
circumvent continued aggression by one animal to
another is suggested by the data. Tension-reducing
grooming may not always be successful in preventing
aggression but for most members of a society its effi-
cacy is impressive. While grooming typically follows
aggression it does not usually precede it (McKenna
1975).
Anatomical Focus of Social and Self Grooming
Hanuman langurs groomed all parts of the body.
From a sample of 693 social grooming bouts the
analysis indicates that those anatomical regions out of
sight or reach of a recipient of grooming were more
frequently groomed by another animal than were ac-
cessible areas. Whereas 55% of the sample involved the
grooming of areas designated inaccessible to the reci-
pient of grooming (see Table 2), 45% of the social
grooming involved accessible areas. Whether or not
social grooming of inaccessible regions promotes
hygiene by removing ectoparasites, thereby decreas-
ing possibility of disease, cannot be quantitatively de-
monstrated but such may be the case. It is important,
however, to consider the context of the initiated bout,
for the data reveal that the context often determines
which part of the body will be groomed. For example, a
ventral-dorsal orientation was assumed by a groomer
and aggressor, respectively in over 75% of the re-
sponses initiated by an attacked animal immediately
following attack. Eye contact was either broken al-
together, or at least avoided in such incidents, and the
social grooming of an inaccessible region of the ag-
gressor's body was initiated by the attacked animal.
While this behavior may prove hygienically beneficial
in the long run, how it comes about can be explained in
terms of the immediate social rewards for each of the
participants.
During relaxed social grooming there is, likewise, a
tendency to avoid body orientations which require sus-
tained and direct eye contact i.e, a ventral-ventral
dyadic orientation. However, as Table 3 reveals, the
proportion of times animals are oriented away from
each other in a ventral-dorsal position is far less than in
the case during tension-reducing grooming (41 % ver-
sus 69% of the total). At least among captive langur
monkeys it can be speculated that the grooming of
inaccessible regions of the body appears to be regu-
lated not strictly by hygienic or health needs but by
social strategies having immediate social consequences
such as suppressing further factionalism and inter-
animal aggression.
Anatomical Area
Back (Dorsum)
-4 Caudal Area
.1 Underarms (Axilla)
e Shoulders
I  Top of Head
Face-Teeth
%of Sample Groomed
22.2%
11.6%
3.6%
3.2%
9.3%
5.5%
T=55.4%
Hands
Forearms
Ventral-Thoracic Area
Posterior-Ventral-Abdominal Area
Hindlimbs
Tail (Medial, Distal)
3.1%
8.6%
11.6%
6.0%
4.0%
11.3%
T= 44.6%
Table 2. -Anatomical foci of social grooming (n= 1,662 receivers of
social grooming)
Ventral-Ventral Orientation
(animals face each other)
Relaxed
Social
Grooming
44%
Tension-
Reducing
Grooming
23%
Ventral-Dorsal Orientation     41%            69%
(receiver of grooming turns
away from actor)
Unclear Body Orientation       15%             8%
Table 3. Percent of relaxed and tension-reducing grooming bouts in
which different body orientations were assumed by grooming dyads
(an actor and receiver).
Anatomical Area
Forearms
Tails
Genitals
Chest (Thoracic Area)
Lower Abdomen
Medial Thighs and Hindlimbs
Hands
Feet
% Groomed
29.7
36.1
8.0
5.0
4.2
8.0
3.0
6.0
Table 4. - Anatomical focus of self-grooming (n=55)
A review of the self-grooming data (Table 4) reveals
that during nonsocial grooming sessions animals pre-
ferred to groom their tails more often than any other
part of their bodies (36% of the sample), while groom-
ing of the forearm followed second in frequency (29%;
Figure 3). The fact that tails were most often groomed
during solitary grooming sessions is understandable
since they were the most vulnerable part of the body.
Cuts and lacerations of the distal and medial aspects of
the tail were frequently sustained. The animals often
caught their tails on parts of the enclosure. Genital
self-grooming was most commonly observed among
the immature males (6%of the 8% total). It was com-
mon for males to sustain an erection during these
grooming periods but none were seen to ejaculate.
7
8
Figui-e 3. An adult female grooms herself while sinmultaneously nursing hei- inifant and sittinig-
in-contact with her three yeai- old adolescent daughter.
Discussion
In Weber's (1973) discussion of tactile commuLnica-
tion among fh-ee-ranging lanigurs groonming behavior
is described as one of nine 'mneaningful comhbinations
of communication sequences." While discussing the
funictions of tactile behaviot s including grooming he
states, " . . . irt these pattet ns social needs of bodily
contact are atticulated and satisfied; they are social
expressions of accepting and being accepted" (Weber
1973:481). Similar to the findings here but not al-
together in agi-eement with them Weber found that
reciprocal grooIning was much more comimon in
"same-sex" subgroups than it was in subgroups con-
taining both sexes and that one-sided gi-ooming by
adtiltfemales of adult males was typical.He proposed
that this one-sidedness of grooming activities occur-
ring between the adults is explained by the fact that
" . . . the interactions between adult males and females
in heterosexual groups are always complimentary"
(Weber 1973:483). Complimentary interactions are
defined in terms of status diffetentials between the
interacting participants. Accoi-dingly, the adult male
is always the receiver (i.e. dominant) in grooming
interactions and, conseqtienitly, does not recipt-ocate.
As actors in groomiing interactions the femiales at-e
always the subordinants. If recipt-ocal gioooniing oc-
curs between aniy two animals, tather than a com-
plimientary t elationship, Weber contends that a
"symmetrical" telationship can be said to exist bet-
ween them (Weber 1973:483).
While Weber may be correct in suggesting that
actor and receiver roles in particular interactional
settinigs may (at times) reflect dominance and subor-
dinance and, thus, are comiplimentaty (his defini-
tion), the data collected here suggest that his explana-
tiOn cannot accurately be applied to all grooming
interactions between the adult male and females, nor
to many of the other social interactions that occLtr
between them. As was shown earlier, adttlt anid inm-
mature nmales frequently groomed adult females and
individual females t-esponded differentially to the
grooming solicitations of the adult male. In the event
that an adult fenmale ignores a grooming invitation
and refuses to groom the adult male (which fre-
quently occurred), using Weber's definition of com-
plimeiitarity the adult female behaves in a dominant
(i.e. passive) role with respect to the adult male who,
in turn, behaves in the suboi-dinant (i.e. actor) role.
The point is that in reference to dyadic situations
complimenitarity is more accurately defined in terms
of what the animals are actually doing with respect to
each other rather than in terms of status differentials
because as a behaviotal index the dominance/
subordinance characterization is often unreliable,
particularly when describing the grooming relation-
ships between male and female adult langurs. So too,
females spend much more time grooming each other
than they spend grooming adult males so it can be
expected that between them much more reciproca-
tion will take place. Furthermore, female-female
bonds established and maintained through reciprocal
grooming may be more closely tied to the other social
roles females perform such as infant caretaking, sol-
iciting sexual behavior, and policing activities rather
than a reflection of a general social position they
occupy with respect to the males (see McKenna 1975).
It is important, therefore, to view grooming behavior
not in terms of status differentials but in terms of how
this behavior reflects role complexes and interrelated
behavior sets that relatively but not absolutely dif-
ferentiate age groups, sex groups, and age and sex
groups combined. By doing so the question of func-
tion is best approached because it forces a more com-
prehensive evaluation of the behavior as it relates to
other social and physical needs.
From this more flexible position the positions of
Alexander (1974) and Freeland (1976) can be consi-
dered. Alexander suggests that in the beginning
grooming behavior controlled parasites and only later
assumed significant social functions. He states,
'That parasite-controlling behavior should acquire a
social role only illustrates the effects of group living
upon the way selection changes behavior ... Such
relationships between selection and different social
functions and effects must be understood if social
organization is to be clarified or traced from the be-
ginning" (Alexander 1974: 331). Freeland takes Ale-
xander several steps further when he hypothesizes
that troop compositions, infant-caretaking behaviors,
sexual behaviors and inter-group relationships are
selected specifically to reduce the acquisition of new
pathogens and to "minimize the pathogenicity of dis-
ease" the individuals of a group might already harbor
(Freeland 1976: 12).
While the data on langurs presented here can
neither verify nor refute these authors' contentions,
they can be useful in assessing the overall feasibility
of their arguments. For example, it was shown that
langurs tended to groom inaccessible regions of the
body rather than accessible regions. This information
and the observations made by Curtin (1975) that solit-
ary male langurs during the wet season suffered from
leach infestation lends support for the hygienic ar-
gument. However, it was also shown that ventral-
dorsal body orientations which expose inaccessible
areas to others for grooming were governed not only
by the immediate social context (relaxed or tense) but
also by the nature of the relationship existing between
the participants. This point is mentioned to dispel
any interpretation which evokes a genetical link bet-
ween grooming behavior and part of the body
groomed.
Probably few investigators will deny that cleaning
the fur can be extremely important particularly when
animals spend much of their time foraging in litter,
swampy areas, or dead wood (Hladik 1975). However,
researchers might argue about the utility of deciding
which function (social or hygienic) was important
first, especially since natural selection does not oper-
ate in a vacuum, nor upon one specific behavioral
strategy at a time. Instead, natural selection works
simultaneously on all the behavioral subsystems
which, to greater and lesser degrees, influence the
species ability to successfully reproduce. My guess is
that structural and physiological adaptations rather
than social ones are more likely to have been initially
selected for in order to control diseases brought about
by ecto-parasites especially since internal parasites
which cannot be removed by grooming are just as
serious a problem. But it seems useless to speculate in
this way since in certain areas parasites and disease
can be as much an ecological limiting factor as the
availability and distribution of food. Consequently,
grooming must be subsumed into a broader context
which includes reference to such behavioral subsys-
tems as feeding and ranging patterns, sexual be-
haviors, rearing practices, predator and incest avoi-
dance, defense strategies and locomotion, all of
which gradually emerged in response to environmen-
tal pressures.
What is needed to test Alexander's contentions and
the sweeping hypothesis proposed by Freeland is a
cross-specific comparison of sympatric species that
must cope with similar pathogens and disease pres-
sures. In areas of intense parasite infestations groom-
ing ought to be elaborated, at least according to Ale-
xander (1974). If not, a determination of what
mechanisms are important in controlling them
should be made. Experimental manipulations of
groups (relocations of groups from areas with diffe-
rent parasite pressures) could reveal the processes by
which such adaptations are made and, perhaps, the
role of grooming as a practical vehicle for parasite
control. Only after acquiring such data can we accu-
rately assess the etiologies of grooming.
Summary and Conclusions
An intensive study of captive Indian langurs (Pre-
sbytis entellus) revealed that grooming behavior was
exhibited more frequently and for greater periods of
time than was any other social behavior. Whereas the
frequency by which adult females initiated social
grooming was much greater than that amount in-
itiated by any other age and sex class, there are impor-
tant intraclass variations and when individual
grooming records are considered, age and sex class
distinctions with respect to grooming become less
absolute. Characteristically, females groomed for
longer periods of time and their grooming networks
were much more extensive. Cutting across age and
9
1 ()
Figures 4 and 5. Relaxed and reciprocal social grooming is exhibited between these two adult
females. In the top photo adult female A (oni the right) grooms adult female B (on the left) in a
venti-al-ventral orientation. In the bottonm photo Animal A has turned away from animal B and
the gtooming roles of the participarnts are teversed and demonstrate a ventral-dorsal ot ienta-
tion.
:) zn t:Ss .: >z3. ': :, t)E .XD vi.u :M> . W:: W6Wv ...  1f3ig. $d>>Xe7 S FXrXilg4 f .':A:%g: : aD.Gg.Sk.:RS .?>S S
sex class boundaries the grooming activities of adult
females may function to enhance group integration
especially since their grooming activities include
immature males whose positions in the group are
socially tenuous.
Social grooming solicitations and the contexts in
which grooming occurred were tremendously di-
verse. While the majority of grooming bouts were
described as relaxed, tension-reducing grooming
which was recognized when one or both of the groom-
ing participants exhibited tense facial expressions or
vocalizations occurred after aggressive interactions,
before and after social mounts, during sexual and
infant-caretaking activities, following social presents
and after ventral-ventral embracing. In addition, it
was found that although grooming invitations or sol-
icitations were not often a part of a tension-reducing
sequence as they were a part of the relaxed social
grooming bouts, in the majority of cases it was the
receiver of aggression who acted the grooming while
the aggressor turned away and received it. The rela-
tionship between grooming and aggression proved to
be an interesting one since a positive correlation coef-
ficient was computed. As the frequency of grooming
increased between individuals so did aggression or
vice-versa. The computation of this statistic reveals
the value of considering context since rarely (if at all)
did aggression follow grooming behavior between
participants. In most instances aggression preceded
it. Hence, grooming seemed to promote the restora-
tion of peaceful relationships between individuals
and the cessation of hostilities. As an appeasement
mechanism the grooming behavior of captive langur
monkeys cannot be underestimated.
With respect to the strong statements put forth by
Freeland (1976), Alexander (1974) and Hutchins and
Barash (1976) on the disease-controlling functions of
grooming behavior these data can neither prove, nor
disprove their contentions. It was, however, stressed
that among langurs the part of the anatomy exposed
by one animal to another is primarily determined by
the nature of the interaction preceding the grooming
bout. Inaccessible areas of the body were groomed
most often after aggressive encounters. More specifi-
cally, ventral-ventral grooming sessions, i.e. groom-
ing interactions that involved the animals facing each
other in which eye-contact was sustained, occurred
most often during relaxed social grooming bouts.
During tense grooming encounters ventral-dorsal
body orientations permitting the avoidance of eye-
contact between grooming dyads were more com-
mon. These facts are relevant to understanding the
circumstances in which inaccessible parts of the body
are sometimes groomed. While this grooming may
function in the long run to decrease disease poten-
attending to it and providing tactile enjoyment while
the recipient of aggression and the actor of the groom-
ing manipulates an aggression-receiving situation
into a peaceful one.
With the present data in mind some tentative con-
clusions can be offered. Among Hanuman langurs
social grooming is intimately fused with almost all
aspects of social life and can be used to manipulate
social situations and to establish important social al-
liances. The argument that grooming originally
evolved as a parasite-controlling mechanism appears
simplistic and ignores the fact that natural selection
works not upon one behavior but on complexes of
behavior and makes continuous compromises on the
efficacy of each adaptive strategy. The "complimen-
tarity" of grooming behavior as defined by Weber
wherein active/passive, dominant/subordinant roles
are ascribed to adult male and female langurs is,
likewise, unsatisfactory particularly since status dif-
ferentials are so fluid in langur society. No doubt
social grooming performs dualistic social and
hygienic functions but given the social base from
which colobines evolved it may prove unwise to
separate the two, especially since both immediate and
long terms benefits are mutually derived.
tials, the actions of both participants (actor and re-
ceiver) provide immediate social rewards; the actor of
the aggression is appeased by the attacked animal
11
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