One of the most distinguishing features of human speech is displaced reference, or the ability to discuss objects and events not physically present at a given time. Although we tend to take this phenomenon for granted, it’s actually quite an impressive feat—for perspective, imagine your pet dog regaling a neighborhood pal with tales of a recent trip to the park by drawing on memories of long-gone ball throws and belly rubs.
Researchers have long believed displaced reference is unique to humans, but as Virginia Morell reports for Science magazine, a new study led by researchers from Scotland’s University of St. Andrews suggests orangutans can “talk” about the past, too.
The team’s findings, published in the journal Science Advances, revolve around seven orangutan mothers tricked into thinking they’d spotted potential predators, which were actually the two scientists, Adriano Reis e Lameira and Josep Call, draped in sheets featuring tiger stripes, spotted patterns and various colors. Over the course of 24 simulated exposures, Lameira and Call recorded 12 instances of mothers shouting warnings to their babies and 12 instances of no shouting at all.
Crucially, Bill Andrews writes for Discover, those that raised the alarm did so after waiting an average of seven minutes, which means that they perhaps shouted out to their friends nearby that there may still be danger lurking, even if it’s no longer in view. (Or perhaps saying: did you see that really strange looking tiger earlier?)
It’s possible the orangutans were so paralyzed by fear that they only regained control of themselves after the threat had passed, but several factors make the researchers suspect the lapse in time was a more calculated move. Some of the orangutan mothers sprang into action upon noticing the threat, grabbing their infants and bringing them to safety; as Morell notes, the quick-thinking primates simply moved quietly in order to not draw attention.
According to Andrews, the authors also observed correlations between lapses in alert time and the mother’s distance from a perceived predator, as well as the age of the infants involved. The closer a predator stood, the lower the likelihood of the orangutans releasing any warning call. Those that did shout out tended to wait longer than those situated at further distances from predators. The younger the baby, however, the more likely its mother was to call out, even if little time had passed since the predator moved away.
The study points toward the warning calls’ status as both a signal of ongoing danger and an educational tool designed to teach offspring about potential threats. Orangutans have already proven themselves highly intelligent—just last week, a separate study published in Scientific Reports showed the close human relatives are better at crafting tools than young children—and as Luntz explains, prior research has suggested they learn by observation instead of relying solely on instinct.
Lameira tells Science that the orangutan’s ability to wait before responding to stimuli is a sign of its intellectual capacities. He posits this skill, in conjunction with the primates’ long-term memory, intentional communication and fine control of the laryngeal muscles, could perhaps one day lead to the evolution of ape language, or some semblance of speech as used by humans.
“Great ape vocal behaviour is underpinned by a much more powerful high-order cognitive machinery than traditionally presumed,” Lameira says in a statement. “The vocal behaviour is not simply a reflex or conditioned response towards danger but a measured and controlled behaviour.”