When a chimpanzee placed a raw sweet potato slice into the device, a researcher shook it, then lifted the top tub out to offer the chimp an identical cooked slice of sweet potato.

It was known that chimps prefer cooked food, but it was an open question whether chimps had the patience to wait through the pretend “shake and bake” process. And, the researchers wanted to know if the animals could understand “that when something raw goes in there it comes out cooked,” said Dr. Warneken.

He and Dr. Rosati, who contributed equally to the research, spent parts of two years at the Tchimpounga Chimpanzee Rehabilitation Center, a sanctuary in the Republic of Congo and ran nine different experiments, judging different cognitive capacities. The two researchers are married to each other.

The chimps showed a number of indications that, given a real cooking opportunity, they had the ability to take advantage of it. They resisted eating raw food and put it in the device, waiting for cooked food. They would bring raw food from one side of a cage to the other in order to put it in the device. And they put different kinds of food in the device.

Dr. Rosati said the experiments showed not only that chimps had the patience for cooking, but that they had the “minimal causal understanding they would need” to make the leap to cooking.

Other scientists praised the research, but the world of research on chimpanzee cognition is a small one, and many of the scientists know each other and have worked together. Brian Hare at Duke University was not involved in the research, but has worked with Dr. Warneken and was Dr. Rosati’s Ph.D. adviser. Dr. Wrangham was his Ph.D. adviser.

He said in an email, “In 1999, when Wrangham proposed the cooking hypothesis, it seemed silly to some to think that the use of fire was the major impetus to convert upright chimpanzee-like creatures into the first species of humans, but this paper makes that scenario the leading hypothesis in my mind.”