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Clapping in chimpanzees evidence of exclusive hand preference in a spontaneous bimanual gesture.

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American Journal of Primatology 68:1081–1088 (2006)
RESEARCH ARTICLE
Clapping in Chimpanzees: Evidence of Exclusive Hand
Preference in a Spontaneous, Bimanual Gesture
ALISON W. FLETCHER1,2
1
Department of Biological Sciences, University of Chester, Chester, United Kingdom
2
Department of Zoology, Miami University, Oxford, Ohio
An increased understanding of spontaneous bimanual tasks performed by
chimpanzees would enhance the ongoing debate on population handedness in this species, and thus shed light on the evolution of hemispheric
lateralization in humans. However, documentation of such bimanual
activities has been largely absent in the literature because such behavior
is infrequently observed in the natural repertoire of this species. This
study presents data on a simple, spontaneous bimanual gesture–
‘‘clap’’–that was investigated in a naturalistic group of 26 chimpanzees
(Pan troglodytes). Sixteen individuals exhibited a total of 657 bouts
of clapping directed toward humans, usually in the context of food
availability. Most individuals were exclusive in their dominant hand
preference, but since there was no population bias to the right or the left,
the population is placed at level 3 of McGrew and Marchant’s [Yearbbook
of Physical Anthropology 40:201–232, 1997] laterality framework. This
is the first reported evidence of level 3 laterality in a non-tool-using task.
Clapping increased in frequency with age, being common in adults,
present at lower rates in adolescents, and absent in infants and juveniles.
There was no effect of rearing or sex. The lack of population bias to the
left or right for this bimanual gesture has implications for the debate on
the evolution of language. Am. J. Primatol. 68:1081–1088, 2006. c 2006
Wiley-Liss, Inc.
Key words: laterality; chimpanzee; bimanual; gesture; clap
INTRODUCTION
The study of lateral bias in primates seeks to improve our understanding of
left-hemispheric specialization and the emergence of language in humans. While
studies of several primate species in this context have been conducted,
investigations into chimpanzee (Pan troglodytes) handedness are by far the most
numerous [McGrew & Marchant, 1997], reflecting the similarity to humans in the
Correspondence to: Dr. Alison Fletcher, Dept. of Biological Sciences, University of Chester,
Parkgate Rd., Chester, CH1 4BJ UK. E-mail: a.fletcher@chester.ac.uk
Received 16 August 2005; revised 12 January 2006; revision accepted 30 January 2006
DOI 10.1002/ajp.20308
Published online in Wiley InterScience (www.interscience.wiley.com).
r 2006 Wiley-Liss, Inc.
1082 / Fletcher
physiological attributes of that species, as well as our common ancestry. Humans
are usually considered to be significantly right-handed at the population level
[Raymond & Pontier, 2004]; however, such assessments are usually based on
measures of tool use, and observations of spontaneous, everyday activities do not
show such a strong bias [Marchant et al., 1995; Murray & Fletcher, 2005].
The degree of hand preference observed in chimpanzees likely reflects several
different factors, as evidenced by its apparent variability in different reports.
It has been shown in simple, unimanual, spontaneous behaviors (i.e., involving
a single continuous movement, such as ‘‘pick up’’ (extend limb and grasp
detached object, then flex limb, in one continuous motion) and ‘‘eat’’ (place object
in mouth)) that some individuals show hand preferences while others do not, and
that there is variation among populations, whether wild or captive [Fletcher &
Weghorst, 2005; McGrew & Marchant, 1997]. Overall, a lack of population
laterality for simple unimanual tasks has been observed. What does seem to be
apparent, however, is that hand preferences for bimanual tasks and tool use (e.g.,
termite fishing, which requires fine motor skills) are more likely. In consideration
of bimanual non-tool tasks, in which both hands are active in a coordinated
manner, captive experimental studies have reported population right-handedness
[Hopkins, 1994, 1995; Hopkins et al., 2003]. The infrequent observation of
spontaneous bimanual hand use in naturalistic and wild populations has hindered
comparisons. However, Corp and Byrne [2004] noted that in wild chimpanzees,
bimanual, multistage processing of Saba and Citrus fruits provides clear evidence,
at the individual level, of one hand specializing in a particular role. Hand
preferences in tool use (whether unimanual, such as wadge-dipping, or bimanual,
such as termite fishing or nut-cracking) have been observed more frequently in
the wild [e.g., Boesch, 1991; Marchant & McGrew, 1996; McGrew & Marchant,
2001; Sugiyama et al., 1993]. Individuals in both wild and captive populations
seem to exhibit some exclusivity of hand preference in tool-using behaviors,
although frequently there is no resulting population bias.
It was recently suggested by Corp and Byrne [2004] that bimanual and toolusing tasks have important similarities that place them apart from simple,
unimanual activities. They suggest that even when lateralized tool-using
behaviors are unimanual, they require spatial and temporal coordination skills,
which are also necessary for bimanual tasks. This raises the question of what
should occur if the behavior is bimanual but relatively simple.
This paper reports on the observation of chimpanzees in a naturalistic
environment performing a simple and spontaneous bimanual gesture, ‘‘clap.’’
This behavior was exhibited by chimpanzees (Pan troglodytes) in Chester Zoo,
apparently to attract the attention of zookeepers or visitors from a distance, and
usually in the context of potential food availability. While ‘‘hand-clap’’ has been
investigated in captive chimpanzees as a gesture exhibited during play (clapping
of hand or wrist [Tomasello et al., 1994], and ‘‘clap’’ has been described as a
means of getting attention from a human experimenter holding food by captive
chimpanzees [Hostetter et al., 2001], the laterality of clapping in apes has been
reported only within a composite measure of communicative gestures (including
‘‘beg’’ and ‘‘point,’’ e.g., in bonobos [Hopkins & de Waal, 1995]).
MATERIALS AND METHODS
Data were collected in 1997 during a comprehensive study of spontaneous
behavior [Fletcher & Weghorst, 2005]. The subjects were 26 chimpanzees that
ranged in age from just over 1 year to 50 years (Table I). They were observed as a
Am. J. Primatol. DOI 10.1002/ajp
Clapping in Chimpanzees / 1083
TABLE I. Number of Bouts of Clap for All Study Individuals in Ascending Order
by Age, Indicating Hand Preference, Significance Level and Rearing Status
Age at start
of study
(years:
Age
Individual
months) class
Rearing
status
No. of bouts
No. of bouts
with left hand with right hand
uppermost
uppermost
Females
CH
HO
LZ
ZE
WH
AL
1:3
1:7
2
3
4
5
I
I
I
I
J
a
MR
MR
MR
MR
MR
MR
LA
KA
WA
SL
SA
KK
FL
MY
FA
HP
RO
6
6
9
9
10
13
17
19
21
22
24
a
a
A
A
A
A
A
A
A
A
A
MR
MR
MR
MR
MR
MR
MR
HR
MR
MR
HR
HE
KT
CL
ME
25
26
26
50
A
A
A
A
HR
–
HR
70
Wild born 48
Wild born –
Males
DY
FR
NI
WI
BO
10
21
28
29
31
A
A
A
A
A
MR
HR
HR
HR
Wild born
–
–
–
–
–
–
–
–
–
–
–
2
7
–
–
–
1
20
–
–
24
95
13
5
31
–
–
8
–
14
19
61
–
46
–
4
–
–
–
100
–
–
–
1
45
–
17
26
Significance
level
–
–
–
–
–
(less than
6 bouts)
P 5 0.016
Po0.001
Po0.001
Po0.001
Po0.001
Po0.001
–
Po0.001
Po0.001
Po0.001
(less than
6 bouts)
Po0.001
Po0.001
Po0.001
–
Po0.001
Po0.001
–
n.s. (P 5 0.108)
Po0.001
A=Adult, a=adolescent, J=Juvenile, I=Infant, MR=Mother-reared, HR=Hand-reared.
naturalistic group in a spacious enclosure, which consisted of a conical, threedimensional indoor viewing area measuring 4.3 m wide and 13 m high, and an
outdoor enclosure of approximately 0.2 ha. Data were collected by two observers,
following informal cross-checking and complete agreement, by focal subject
sampling from a distance of 1–40 m. The behavior reported here (‘‘clap’’) is
defined as follows: One hand is brought forcefully downwards, palm facing down,
to strike other hand, palm facing upwards; upper hand is recorded as dominant
(Plate 1). This definition has been used in similar ethological studies of wild
chimpanzees [Marchant & McGrew, 1996; McGrew & Marchant, 2001]. Only the
first instance of this behavioral pattern was recorded when it happened in series,
to ensure independence of data points. An intervening bout of another behavior
had to be performed before ‘‘clap’’ was recorded again. Binomial analyses were
used to establish handedness. Statistical tests were all two-tailed with the
Am. J. Primatol. DOI 10.1002/ajp
1084 / Fletcher
Plate. 1. ‘‘Clap’’ with the right hand dominant in adult female chimpanzee Heidi (HE).
significance level set at Po0.05. For an individual to be included in statistical
analyses, his/her clap frequency had to be at least six bouts.
RESULTS
In total, 657 bouts of ‘‘clap’’ were recorded. This bimanual gesture was
always performed with either the left or right hand in the dominant, uppermost
position, and was performed in a sitting or bipedal position. All but one of
16 individuals that performed this gesture above the criterion of six bouts needed
for statistical analysis displayed a significant hand preference, and 12 of 16
individuals were always consistent in their preference of uppermost hand
(Table I). In those that were not consistent, the inconsistencies were minor,
and recorded as follows: SL 1/62 bouts, DY 1/32 bouts, and MY 4/28. The pattern
of dominant hand preference was spread fairly equally, with eight showing a right
preference and seven showing a left preference. There was no effect of sex
(Z 5 0.356, n 5 26, n.s.) or rearing status (Z 5 1.408, n 5 26, n.s.).
The majority of adults performed ‘‘clap,’’ and this behavior increased with
age (rs 5 0.400, n 5 26, P 5 0.043; rs 5 0.524, n 5 25, P 5 0.007 after removal of
ME, who was 50 years old and stiff, with reduced mobility). There was no
Am. J. Primatol. DOI 10.1002/ajp
Clapping in Chimpanzees / 1085
2.50
Bouts per day
2.00
1.50
1.00
0.50
0.00
0.0
10.0
20.0
30.0
40.0
50.0
60.0
Age (years)
Fig. 1. Relationship between the mean frequency of ‘‘clap’’ and the age of the individual.
evidence of this behavior in infants or juveniles, and fewer bouts were performed
by adolescents than by most adults (Fig. 1).
DISCUSSION
The pattern of observed hand use represents exclusive hand preference in
a significant majority of the individuals that engaged in clapping. In McGrew and
Marchant’s [1997] framework of lateralization in nonhuman primates, this
represents level 3. Briefly, this framework categorizes populations of individuals
as follows: At level 1, essentially all individuals are ambidextrous; at level 2 there
is a significantly specialized proportion of individuals but the population is
unbiased as a whole; level 3 exists when the population distribution remains
unbiased to the left or right despite a significant proportion of exclusivelyspecialized individuals; at level 4 the majority of lateralized individuals are biased
to either the left or right; and at level 5 most individuals are exclusivelyspecialized to the left or right. Level 3 lateralization has not previously been
reported for spontaneous unimanual tasks in primates, although it has been
observed in several studies of spontaneous tool use [Boesch, 1991; Goodall, 1968;
McGrew et al., 1999; Sugiyama et al., 1993]. Thus, the handedness observed
in chimpanzee clapping would seem to lend further support to Corp and Byrne’s
[2004] suggestion that bimanual tasks necessitate a degree of skill similar to that
needed for tool use.
Clapping in chimpanzees is also of note in terms of its gestural function.
Manual gestural communication in chimpanzees is of particular interest in the
debate on the evolution of language in humans, and several models have been
proposed to explain the origins of left-hemispheric specialization for human
language [Bradshaw & Rogers, 1993; Corballis, 2002]. Some studies in apes have
reported a population right-hand bias in gesture use [e.g., Hopkins & Carriba,
2002], particularly when the gestures are accompanied by vocalizations [Hopkins
et al., 2005; Hopkins & Cantero, 2003], and claim support for Corballis’s [2002]
proposal that hemispheric lateralization in humans evolved from a pre-existing
manual communication system in ancestors we share with chimpanzees.
However, data are lacking for hand preference in bimanual gestures of
chimpanzees, such as drumming on objects, probably because these tend to
occur at a low frequency [e.g., Fletcher & Weghorst, 2005] (McGrew and
Am. J. Primatol. DOI 10.1002/ajp
1086 / Fletcher
Marchant, unpublished data). However, bimanual clapping was seen daily in the
Chester population and was observed in the majority of adults, with no apparent
sex or rearing differences. The lack of population right-hand bias for this
spontaneous gesture contrasts with the aforementioned captive studies of
complex bimanual tasks and unimanual gestures, and thus does not provide
support for Corballis [2002], but is consistent with an overall lack of populationlevel handedness in spontaneous, unimanual (non-tool) behaviors observed in this
population [Fletcher & Weghorst, 2005]. The audible nature of ‘‘clap’’ enables an
individual to gain the attention of an observer without first establishing visual
contact, unlike pointing and food begs. The fact that other simple bimanual
gestures previously recorded for apes are also auditory (e.g., ‘‘clap,’’ ‘‘chest-beat,’’
and ‘‘slap ground’’ in bonobos [Pika et al., 2005]) suggests that a detailed
investigation of lateral bias in these gestures may be worthwhile to test proposed
models of the emergence of left-hemispheric specialization in human language.
It has been suggested [McGrew & Marchant, 1997] that when humans
interact regularly with chimpanzees, the hand preference of the humans may
influence that of the chimpanzees. Since the Chester chimpanzees are regularly in
visual contact with humans, it is not implausible that hand preference in humans
may have had a subtle influence on these chimpanzees, given the interspecific
nature of the gesture. However, without investigating hand preference for
clapping within the general human population, and the frequency with which
chimpanzees observe clapping in humans, it is impossible to make an informed
judgment.
There was a clear effect of age for ‘‘clap,’’ with the younger individuals failing
to exhibit the behavior at all, and adolescents clapping infrequently. In Tomasello
et al.’s [1994] study, individuals as young as 1 year old engaged in ‘‘hand-clap’’
(clapping of one’s own hand or wrist) with their conspecifics during play, which
suggests that the basic motor pattern is possible in this age group. The regular
performance of ‘‘clap’’ by older individuals, and its frequent association with food
suggest that intraspecific social learning is likely to be involved in the
development of this behavior in the Chester individuals. However, there may
well have been a human element in its original emergence, since some of these
individuals were hand-reared. Indeed, in a group of bonobos, ‘‘clap’’ was
performed only by individuals that were raised by humans [Ingmanson, 1987].
However, the lack of rearing effect and the late development of this behavior
suggest that there are other factors at work. In a study of intentional
communication, Leavens and Hopkins [1998] found that juveniles were less
likely to engage in face-to-face interactions with adult male, communicative
humans, even though those that did gesture did not differ from older individuals
in the type of gestures performed. The facts that ‘‘clap’’ was not seen in the
context of play in the current study, and that only older individuals were observed
to perform this behavior may support the notion that the emergence of
intentionality as a cognitive ability is the key element that is necessary for the
performance of this gesture during interaction with humans, rather than the
physical capability to perform the motor action.
Hand preference during the immature period, as observed during tool use
and complex bimanual tasks, appears to be changeable [e.g., Boesch, 1991; Colell
et al., 1995; Fletcher & Weghorst, 2005; Hopkins, 1995], and consistent hand
preferences are not evident until adolescence or adulthood. This is likely to be due
to the involved nature of such tasks, which may take some time to master fully
(e.g., bimanual processing of Saba fruits [Corp & Byrne, 2002]). Changes in hand
preference in an individual may represent development of the method used (e.g.,
Am. J. Primatol. DOI 10.1002/ajp
Clapping in Chimpanzees / 1087
learning to crack nuts [Boesch, 1991]). Of note in the current study, for the three
immature individuals that did perform ‘‘clap,’’ there was some evidence of
exclusive hand use from the start, albeit from a small number of bouts. Although
only a longitudinal study can confirm consistency of hand use for ‘‘clap’’ through
immaturity and into adulthood, Hopkins and Leavens [1998] found in an
experimental study of gestures that a greater number of older chimpanzees
gestured (food-begs and pointing) with the right hand than younger ones;
however, that conclusion was based on only one observation on each individual.
If it is assumed that all adult cohorts tested in this way are likely to be similar
in exhibiting an overall hand preference for gestures (and a right-hand bias has
been noted in several such experimental studies of gesture use [e.g., Hopkins &
Cantero, 2003; Hopkins & Carriba, 2002], particularly for food-begs [Hopkins &
Wesley, 2002]), a lack of bias in the immature group suggests that some
maturation of hand preference for gestures may occur during the immature
period, as it does for bimanual tasks and tool use. The later emergence of ‘‘clap,’’
and the apparently fully matured lateral bias that was observed even within
younger individuals suggest a different course of development for ‘‘clap’’
compared to other gestures and bimanual activities, which may be linked to
both its physical simplicity and its communicative, attention-seeking nature.
ACKNOWLEDGMENTS
I thank Chester Zoo for permission to conduct this study, J.A. Weghorst
for joint data collection, and W.C. McGrew for advice on issues pertaining to
these observations. I also thank the anonymous reviewers for helpful comments
on the manuscript.
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