Wow. It has been quite some time since I've posted, and I'm sorry for that. I blame my essays and Boston Legal for it.
Anyway, here's the second part of my summary.
In the second chapter of his (2008) book, Michael Tomasello takes a look at the intentional communicative acts of non-human primates such as chimpanzees.
The question Tomasello asks is this: what are the psychological motives underlying these acts and in how much do they differ from those produced by infants?
Tomasello first differentiates between communicative displays and communicative signals.
Communicative displays are inflexible and involuntary, like a deer's horns or and or a peacock's tail, that deter competitors or attract mates, respectively. The important thing is that these displays are controlled by evolutionary processes over a long period tof time and not by the individual.
Communicative signals on the other hand, are produced, voluntarily and intentionally. The main characteristic of a communicative signal is that the communicator use it to influence the behavior of a single or multiple recipient(s). The communicator is thus actively directing his communicative signal at someone.
An interesting question now regards the famous alarm calls of some monkey species, e.g. the different alarm calls vervet monkeys make when they see a leopard, an eagle, or a snake.
Here's a video of vervet alarm calls, if you're interested:
As Tomasello points out, these calls are mostly involuntary and not very flexible.
The only flexibility regards the so called Audience Effect. This means that
“ individuals may not give certain calls when they are alone or without kin, as opposed to in the presence of others or with kin, but other animal species also refrain from alarm calling in these situations as well (including prairie dogs and domestic chickens; see Owings and Morton 1998), and so one may easily imagine that this is part of the genetically fixed adaptive specialization.“
In addition, there is evidence that cross-fostered macaque species are able to comprehend the signals of the other species, but not to produce it themselves.
Another important difference between human communicative signals and that of other primates is illustrated by the following example: when macaque mothers see (fake) „predators“ approach their offspring, they do not give an alarm calls when they themselves are not at risk (Cheney & Seyfarth 1990).
Vervet Monkeys too, mostly ignore the audience and continue giving alarm calls even when all other monkeys are in a safe position.
For Tomasello and other researchers this clearly shows that the vocalizations of non-human primates are not recipient-directed. Thus, they are to be judged as communicative displays.
Gestural signals, on the other hand, are much more flexible:
„individuals typically produce a gesture only when the recipient is appropriately attentive, and afterward they often monitor the recipient’s reaction and wait for a response;“ (Tomasello 2008: 21)
Also, ape gestures can be put into two broad categories: intention-movements and attention-getters.
In their social interactions, for example, chimpanzees raise their arms toward another chimp and start hitting her to initiate play or place their hand under her mouth and begin to take food to request food.
They also use gestures to get the others attention, for example by slapping the ground and looking at another chimp or by poking him or throwing stuff at him
Although we may find this behavior quite funny and daring to look at, it is still a remarkable fact that primates do this, as these kinds of gestures
„are not widespread in the animal kingdom; they may even be unique to primates or even great apes“ (Tomasello 2008: 27)
What is even more interesting that apes also string sequences of gestures together and combine both
attention-getters and intention-movements.
Although there is no evidence for a kind of „grammar“ for these sequence s (Liebal et al. 2004) it is still a very interesting phenomenon, especially as evidence for any combinatorial structure in primate vocalizations is confined to only two species (Zuberbühler 2002).
In summary, ape gestural communication is quite sophisticated and even has some kind of structure, even if its not something resembling the grammar of human language:
“check the attention of other > walk around as necessary > gesture > monitor the reaction of other > repeat or use another gesture.“
They are thus definitely to be judged as communicative signals.
Things such as attention and reaction monitoring seem to be an important part of the answer to the question
Cheney, D. L., and Seyfarth, R. M. (1990). Attending to behaviour versus attending to knowledge: Examining monkeys’ attribution of mental states. Animal Behaviour, 40, 742–753.
Liebal, K., Call, J., and Tomasello, M. (2004). The use of gesture sequences by chimpanzees. American Journal of Primatology, 64, 377–396.
Owings, D. H., and Morton, E. S. (1998). Animal Vocal Communication: A New Approach. Cambridge: Cambridge University Press.
Tomasello, Michael (2008): The Origins of Human Communication. Cambridge, MA; London, England: MIT Press.
Zuberbühler, Klaus (2002): A syntactic rule in forest monkey communication. In: Animal Behaviour 63, 293–299.