This is an important finding, just published, about orangutan language. The popular press article about it is quite good too.
One of the defining features of language is displaced reference—the capacity to transmit information about something that is not present or about a past or future event. It is very rare in nature and has not been shown in any nonhuman primate, confounding, as such, any understanding of its precursors and evolution in the human lineage. Here, we describe a vocal phenomenon in a wild great ape with unparalleled affinities with displaced reference. When exposed to predator models, Sumatran orangutan mothers temporarily suppressed alarm calls up to 20 min until the model was out of sight. Subjects delayed their vocal responses in function of perceived danger for themselves, but four major predictions for stress-based mechanisms were not met. Conversely, vocal delay was also a function of perceived danger for another—an infant—suggesting high-order cognition. Our findings suggest that displaced reference in language is likely to have originally piggybacked on akin behaviors in an ancestral hominid.
As thee authors describe:
The data (and simple common sense if we imagine ourselves facing a wild Sumatran tiger!) suggest that to respond vocally in the presence of a predator would have been a huge risk to the orangutans’ safety.
If the females had responded immediately by calling out warnings, the predator could have detected them and perhaps attempted an attack, particularly on the infant orangutans.
Instead, the mothers waited for a significant amount of time before signalling vocal alarm about the danger that had now passed.
The question that springs to mind, then, is: why did the females signal their alarm at all? If they hadn’t responded vocally at any point, they wouldn’t have faced any danger at all, right?
That is undoubtedly true; but had the mothers not expressed alarm, their infants would have remained oblivious to one of the most lethal dangers in the rainforest.
Instead, the females waited long enough until it was safe to call out, but not so long that their infants could not connect their mothers’ vocal distress with what had just happened, and understand that it was extremely dangerous.
The female orangutans were teaching their young about the dangers in the forest by referring to something that had happened in the (recent) past.