Group-specific gestures

Gestures that are found to be limited to a specific group can be evidence for local traditions within those groups, and for social learning of gesture. These types of gesture seem to be very rare in all ape species (see Call and Tomasello 2007), thus strengthening either the argument that gestures are ritualized by the same process regardless of which population an individual is in or that gestures are heritable movements shared by all members of a species that become used as gestures once recipients learn to predict the signaller’s subsequent behaviour from their movements. Group-specific gestures can be an important tool in determining how movements become used as gestures as they shed light onto whether social learning can play a factor in shaping the development or expression of certain gestures.

In this study, four gestures were used intentionally by more than one individual in the same population, but not by any individuals in other zoos (Table 17). These gestures were deemed to be “group-specific.” All four of these gestures are unusual, however, and each must be examined carefully in order to determine whether it is indeed a group specific gesture. All four gestures were each found in only two individuals in their group. This means that none of these “group-specific” gestures are common, even within a single population. Their rarity increases the likelihood that they exist in other populations but were never observed in an overtly intentional usage.

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The likelihood of the four observed gestures’ being truly limited to one group is complicated by the fact that three of the gestures are facial expressions. I considered facial expressions to be potential gestures if they were initiated and ended while the signaller was facing the recipient and made no other movements during the expression. They were then subjected to the same criteria of intentional use as all gestures made with other parts of the body. Three facial expressions that met the criteria for intentional gestures were found only in one zoo. Each of these expressions was observed in at least one other zoo as a facial expression accompanying a manual gesture but were never observed on their own. The expressions were only used as gestures unaccompanied by other movement in a single population each. It is possible that two individuals in a population found that a particular expression could communicate their desires on its own as well as when it accompanied a manual gesture.

Table 17: GROUP-SPECIFIC GESTURES.

The modalities of each gesture are given as well as the group in which they were observed. None of the gestures was observed frequently enough to be analysed for meaning.

Gesture Count Modality Group Meaning

Lip smile (tense) 9 Visual (facial

expression) Apenheul —

Pout 5 Visual (facial

expression)

Twycross —

Tongue out 4 Visual (facial

expression)

Twycross —

Tandem walk 18 Tactile Twycross —

The manual gesture tandem-walk is an unusual gesture as it has been observed in all three populations but only seemed to be used as an intentional gesture in one of them. The action involves the signaller placing his hand on the shoulder or back of the recipient during side-by-side locomotion. The action often does not have an obvious goal, and instead may arise during an immature’s transitional stage from being carried to walking independently. Alternatively, it could be used to guide the recipient during locomotion and to indicate a common destination. When tandem-walk met the criteria for

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intentionality, the action was accompanied by looking towards the recipient’s face, and was alternated with pushing or pulling if the recipient did not move. The gesture was used intentionally and often by one juvenile (5.5-years-old) to guide his mother or position her between him and the adult male. One adult female in the same group used it in a similar way to guide her infant. Individuals (particularly immatures) at other zoos were observed placing a hand upon another’s back during side-by-side walking, but the touch was not accompanied with any indication of intentionally communicative use. It may be the case that two animals at Twycross have begun to use a natural reaction to tandem locomotion as a signal; however, it is also possible that this “gesture” is a reactive and not communicative action and the examples of intentional use are unusual examples.

None of the gestures observed in only one zoo make a good case for local traditions or culturally-transmitted forms. The facial expressions are unique to one zoo only in being used without an accompanying gesture, and the low numbers of

observations of the three expressions indicate that they are only rarely used on their own. The fact that each gesture was only observed in two individuals does not make a strong case for different cultural traditions at the different zoos. If the two signallers for each gesture used the gesture to communicate only with the other, one could argue that the actions had taken on meaning as gestures within certain dyads. However, none of the gestures were confined to a single dyad, though each were used by only two signallers. Most problematic is the fact that each of the actions was observed in other zoos, just not in a manner that fit my criteria for intentional usage. The use of the movements in other zoos, coupled with the infrequent use of three of the four gestures, leaves open the possibility that the actions were used as intentional gestures in the other zoos but were not observed frequently enough to be detected by the observer.

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