He gave Indah and Azy a choice between two bowls of grapes. One bowl held more. But there was a trick: The bowl they pointed to first was taken away, and they were left only the grapes in the other bowl to eat. Instinct argued to pick the bigger bowl of grapes first, but the orangutans learned this game wasn't that simple.

They needed to grasp that less would get them more. It's a counterintuitive, complex rule, yet Shumaker says his orangutans quickly understood it -- without coaching. They now choose less to get more almost every time.