When they’re in captivity, great apes usually spend a long time exploring new objects. But researchers knew little about how that curiosity might play out in the wild.

Previously, scientists had planted novel items throughout the forest at Suaq Balimbing, a protected biodiversity area in Sumatra whose orangutans are monitored by conservation biologists. But during those earlier experiments, the apes were so cautious of the new items that the experiments failed.

More recently, the biologists came up with a more enticing way to spark the orangutans’ curiosity, planting a piece of tree trunk filled with local forest honey on trees near the orangutans. Then scientists watched as the apes encountered the familiar but intriguingly novel object during 170 trials.

The ways the orangutans expressed their curiosity varied by age, the biologists found. Immature orangutans looked “significantly longer” at the object vs. other apes, checking it out for an average of 233 seconds compared with 103 seconds for mothers and 34 seconds for sexually mature males. Immature orangutans also were quicker to approach the object and show agitation while doing so.

The apes rarely touched the branch, often using a tool such as a stick to do so. They were also less likely to approach the honey-stuffed branch in areas where food was abundant.

But social connections seemed to influence their curiosity: When an orangutan was accompanied by another ape, it was more likely to approach and touch the object.

In a news release, the researchers say the study’s results shed light on how human curiosity may have evolved.

“We often think of learning and innovation as solo acts, but this might not have been the case in our early history,” said Caroline Schuppli, director of the orangutan research project at Suaq Balimbing and the study’s first author. “If novelty was the spark, then our social lives might have provided the accelerant.”