Any lingering doubts about orangutans' intelligence, this should now settle it. Only a few days after the world learned these great apes can quickly solve problems that baffle half of human seven-year-olds, we have evidence they can teach their offspring about absent dangers. This is regarded as a key stepping stone to human language and has never been previously witnessed in wild animals.

Predator warnings are a major reason for social animals to stick together, but is restricted to threats that can be seen, heard, or smelt.

The human capacity to go beyond this is known as “displaced reference”, defined as the capacity to convey information about “things that are remote in space and time.”

Dr Adriano Lameira of the University of St. Andrews placed models of four predators in the Sumatran jungle and observed the response of orangutan mothers with children at least 5 years old. The models were removed after 2 minutes. The mothers waited up to 17 minutes after the model had been taken away to sound an alarm call, while slowly climbing higher into the canopy, but once they started, kept it up for an average of 25 minutes. 

The time between the “predator” appearing and the mother calling was related both to her height in the trees at the time, and her child's age. In Science Advances, Lameira interprets this as indicating a mother safely in the canopy was more comfortable alerting predators to her presence, and priority was given to warning younger children.

In other words, the paper argues, on first seeing a predator, the mother orangutan chooses to keep silent to avoid drawing attention. Once the threat is out of view, the mother wants to draw the child's attention. The big cats that prey on orangutans are predominantly ambush predators, more dangerous when hiding than visible.

Lameira proposes the mothers' calls not only to warn the child about an ongoing danger, but as part of the process of educating her offspring about future threats. As the wonderful Orangutan Jungle School shows, orangutans are human-like in the proportion of life skills they learn by observation, rather than relying on instinct. Lameira's theory relies on the capacity of the child, as well as the mother, to comprehend the concept of a displaced threat.

A possible previous example of displaced reference has been seen in vervet monkeys, but is thought to represent tactical deception, similar to telling someone to look behind them before snatching their cake, rather than a reference to a real, but absent, threat. Honey bees' waggle dances refer to flowers beyond the range of visibility. However, the brain operations involved are so different from those in humans these are also not regarded as displaced references, making Lameira's observations unprecedented, aside from among captive apes trained by humans.