By David Leavens
Recently, van der Goot, Tomasello, and Liszkowski (2014) reported that human infants, but not great apes, pointed to desirable objects from a distance. The 10 apes in their study all moved as close as possible to desirable food before gesturing to it. They concluded that the babies who pointed from a distance did so because they had an advanced, human-unique understanding of a shared psychological space with the experimenters (“common ground”). We wanted to see whether chimpanzees would sometimes point from a distance, like the babies in van der Goot et al. (2014).
We exposed 166 chimpanzees to (a) desirable food and (b) a human experimenter, presented outside their enclosures, at an angular displacement. We measured whether or not they gestured, the target of their gesture (the food or the experimenter), counting only gestures that were accompanied by alternation of gaze between the food and the experimenter. We administered four trials to each chimpanzee. Because van der Goot et al. (2014) administered different distances to the humans (.95 to 1.8 meters) and the apes (6.0 meters) in their study, it is ambiguous whether the ape/human differences they reported were attributable to their different evolutionary backgrounds or simply these different distances. Therefore, we matched the distances they used with human babies, presenting desirable food to chimpanzees at 1.0 to 1.5 meters.
We found that, like the human babies in van der Goot et al.’s study, half of the chimpanzees approached the food, and half of them pointed towards the food from a distance–there were no statistical differences between our chimpanzees and the human babies in the study by van der Goot et al.
Thus, chimpanzees do, in fact, frequently indicate referents from a distance. We conclude that either (a) van der Goot and her colleagues are correct to use communication distance as an index of advanced psychological representations of a shared psychological space, and therefore this appreciation of common ground is a primitive psychological capacity that we share with great apes, or (b) communication from a distance does not illuminate the psychological processes supporting gestural communication in either apes or humans. We favor the latter interpretation, but whether distance of signaling does or does not index a psychological appreciation of common ground, our findings clearly demonstrate that chimpanzees do not perform differently from human babies, therefore there is no scientific evidence for a psychological difference between humans and apes in their signaling behavior in these situations. Although we found distal signaling from the very first trials in our sample of chimpanzees, we think that a better approach, when faced with divergent results between humans and apes, especially small groups of apes, is to specify the kinds of experiences apes require to match performance with humans. If no amount of training can produce equivalent performance, then there might be a real species difference; if, on the other hand, the capability can be demonstrated in non-humans, then there is no basis to conclude that the capability is unique to humans.
This post is a summary of the article “Distal Communication by Chimpanzees (Pan troglodytes): Evidence for Common Ground?” published in Child Development (2015; published online in advance of print). The research, funded with research grants from the National Institutes of Health and a Grant Development Award from the School of Psychology, was carried out by Dr David Leavens and collaborators from the University of Texas MD Anderson Cancer Center, and Georgia State University.