The centers have some orangutans that were raised as pets and then got too big to handle, and others who came from the wild, where palm oil plantation development had wiped out their home territory.

First they exposed them to new foods and plastic snakes and other novelties.

The ones who had spent their youth in the forest, learned the lessons of caution well. They didn’t try new foods, avoided the fake snake and in general showed the expected lack of curiosity.

Which makes sense. “Imagine you were dropped in the middle of a rain forest,” said Dr. Damerius. It would be unwise to touch all the plants, let alone pop them in your mouth.

But the orangutans raised by humans or brought to a rehab center at a young age experienced a relatively safe environment and human role models who were themselves curious. They were far more likely to eat the dyed purple rice or potato mush, and to investigate a fake snake.

In the second part of the experiment, the researchers used a variety of cognitive tests, requiring the apes to figure out how to open a box, or reach into a chamber in an awkward way to get a treat, or other tasks.