If you give a chimp an oven, he or she will learn to cook.
That's what scientists concluded from a study that could help explain how and when early humans first began cooking their food.
"This suggests that as soon as fire was controlled, cooking could have ramped up," says Alexandra Rosati, an evolutionary biologist at Yale and a co-author of the study, which was published in the Proceedings of the Royal Society B.
Evidence suggests early humans learned to control fire between 400,000 and 2 million years ago.
Rosati and Felix Warneken, a psychologist at Harvard University, carried out the study at a chimpanzee sanctuary in the Democratic Republic of the Congo. First, the researchers gave the chimps a device that appeared to work like an oven.
"You can think of it as a chimpanzee microwave where, basically, if the chimpanzees placed raw food in the device and then we shook the device, [the food] came out cooked," says Rosati, who will be moving from Yale to Harvard this summer.
The device was actually just a bowl with a false bottom that held cooked food. The researchers didn't use fire because it could have injured the chimps, and because some chimps might have already seen how humans used it to cook food.
After providing the "oven," Rosati and Warneken gave the chimps slices of uncooked white sweet potato. "At first, the chimps pretty much ate the food. But then you almost could see them have this insight like, Oh, my goodness, I can put it in this device and it comes back cooked," Rosati says.
About half the chimps became regular users of the faux oven, Rosati says. And those chimps pretty much ignored a second device that returned their food uncooked.
Other experiments showed that chimps understood the concept of cooking.
When researchers gave them a cooked potato slice, they simply ate it. But when they got a raw carrot, they immediately put it in the device. And their preference for cooked food was so strong that they would hold on to raw potatoes, or carry them to other locations, in order to have them cooked.
Previously, chimps and their close cousins, bonobos (like Kanzi, who is pictured above), have been taught to cook by people. But this is the first study showing that animals can acquire a cooking-like skill on their own.
The results add to a debate about whether early humans had the brain power to figure out cooking, an activity that requires planning, a willingness to delay gratification and sophisticated use of a tool, Rosati says.
The new study was inspired by the work of a colleague at Harvard, Richard Wrangham, a professor of biological anthropology. His book Catching Fire: How Cooking Made Us Human argues that early humans began cooking almost immediately after learning to control fire, something Wrangham believes happened about 2 million years ago.
The new study suggests that even back then, our ancestors had brains that were ready to barbecue, Wrangham says. "All they needed, I think, would be to see a piece of food drop in the fire, pick it out and realize that it tasted good, and then the cultural transmission of that behavior would spread very quickly," Wrangham says.
The study also offers a reminder that very few behaviors are uniquely human, Wrangham says. "What we're seeing here is that the chimps are surprisingly similar to humans, even though the whole process of cooking seems like something that is a huge divide between humans and other animals."
MELISSA BLOCK, HOST:
When early humans began cooking their food, life got a lot better. Cooked food is easier to digest. It provides more energy and may have been a critical step in developing bigger brains. It's been unclear though when our ancestors learned to cook. Now NPR's Jon Hamilton reports on a study that provides a hint.
JON HAMILTON, BYLINE: Our human ancestors probably learned to control fire at least 400,000 years ago. That doesn't mean they were using it to cook, though. Alexandra Rosati, an evolutionary biologist at Harvard, says cooking isn't easy.
ALEXANDRA ROSATI: You have to be able to think ahead. You know, I'm going to want to save this raw food I have right now in order to cook it later. You might need to have some self-control to prevent yourself from eating this tempting food.
HAMILTON: And you have to understand that fire is a tool that can be used for cooking. Rosati says grasping all that takes a lot of brainpower, and early humans had brains that were only slightly larger than a chimpanzee's. So to see whether these early humans would have been capable of cooking, she and a colleague did an experiment with chimps. The researchers went to a chimp sanctuary in the Democratic Republic of the Congo. They gave the chimps there a device that worked like an oven.
ROSATI: You can think of it as a chimpanzee microwave where basically if the chimpanzees placed raw food in the device and then we shook the device, it came out cooked.
HAMILTON: The device was really just a bowl with a false bottom to conceal the cooked food. The researchers didn't use fire because it could have been dangerous. Also, they were concerned that some chimps might have already seen humans using fire to cook. Rosati says once the animals got their microwave, she and her partner gave them slices of uncooked white sweet potato.
ROSATI: At first, the chimps pretty much ate the food, but then you almost could see them have this insight like, oh, my goodness, I could put it in this device, and it comes back cooked. And sometimes, they would even get very excited the first time that they managed to do it.
HAMILTON: The cooked potatoes tasted a lot better, and about half of the chimps became regular users. Rosati says these chimps had no interest in a second device that returned their food uncooked. Another experiment suggested the animals really understood what the cooking device could do. When they got a raw carrot instead of a raw potato, they tried to cook that too. And their preference for cooked food was so strong that they would hold on to raw potatoes or carry them to other locations in order to have them cooked. Rosati says the results are highly suggestive.
ROSATI: Because chimpanzees have these skills, this suggest that the last common ancestor of humans and other apes also may have had these skills. So this suggest that as soon as fire was controlled, cooking could have ramped up.
HAMILTON: The study was inspired by the work of Richard Wrangham, a professor of biological anthropology at Harvard. He believes early humans did begin cooking almost immediately after learning to control fire. Wrangham says the new study provides evidence that even 2 million years ago, our ancestors had the brainpower to figure out cooking.
RICHARD WRANGHAM: All they need, I think, would be to see a piece of food drop in the fire, pick it out and realize that it tasted good, and then the cultural transmission of that behavior would spread very quickly.
HAMILTON: Wrangham says he was surprised, though, that chimpanzees had the self-control to hold on to raw food rather than eat it. He says that sort of restraint is something modern humans often seem to lack.
WRANGHAM: You quite often find that whoever's been doing the cooking doesn't really want to eat because they've been eating so much, nibbling along as it gets cooked.
HAMILTON: Wrangham says the study also shows how sophisticated chimp behavior can be.
WRANGHAM: What we're seeing here is that the chimps are surprisingly similar to humans even though the whole process of cooking seems like something that is a huge divide between humans and other animals.
HAMILTON: The new research appears in the journal Proceedings of the Royal Society B. Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.