Think of your favourite dish. Crispy Belgian waffle? Perhaps a gooey grilled cheese sandwich? Or a perfectly cooked steak? No matter what foods you prefer, chances are your dream meal features foods that have been cooked. No other species in the world can control fire, and fire is the engine of cuisine. It's even been argued that one of the defining characteristics of the human species is that we cook our food.

All human cultures incorporate cooking into their meals in some way, and as a result, our species has a suite of adaptations in the mouth and digestive tract for consuming foods that have been transformed from their initial raw state. But one question that researchers have taken up recently is just how early cooking emerged in human evolution. How long were early hominins controlling fire before they realised they could use it for gastronomical gain?

It's not a trivial question. When foods are cooked, our bodies can suck up more nutrients and energy from them. And brains are "energetically expensive" – so it could be that cooking allowed humans to get more energetic bang for their culinary buck, leading to the evolution of bigger brains.

But cooking calls for more than fire and a recipe. For one thing, it requires cause-and-effect reasoning: a chef has to understand that applying heat actually causes a raw vegetable to become cooked. It also requires patience: a chef needs to wait for the raw food to become cooked before sitting down to feast.

Our closest relatives the chimpanzees (Pan troglodytes) don’t cook, and they don't control fire like we do. However, some populations do seem to have at least a basic understanding of how fire works: after a wildfire burns through their habitat, for example, some chimps have been seen seeking out roasted seeds. And if chimps possess the psychological requirements for cooking, then it's possible that our early human ancestors did too – and that would suggest cooking came along quite soon after the control of fire.

To shed more light on some of these questions, psychologists Felix Warneken and Alexandra G. Rosati set off for the Tchimpounga Chimpanzee Sanctuary in Republic of Congo to carry out a series of experiments. First off, they wanted to see whether the sanctuary's chimp residents even preferred eating cooked foods in the first place. Sitting across a table across from a chimpanzee (separated by wire mesh for protection), the researchers would offer a chimp two slices of sweet potato, one raw and one that had been roasted for about 90 seconds.

The chimps chose to gobble up the cooked potato instead of the raw one 88 percent of the time, suggesting they might have the psychological motivation to wait for foods to become cooked. In a second experiment, the chimps were willing to wait for cooked potatoes 85% of the time, even when they could eat a raw potato without waiting. That's an impressive amount of patience for a chimpanzee!

The next experiment asked whether the chimps truly grasped the transformative nature of cooking: that the food itself changes from raw to cooked. Here, the chimps watched as researchers placed pieces of raw potato inside two "mock oven" devices – only one of which actually returned a cooked potato at the end. Showing that they really understood the way that cooking works, the chimps asked the experimenter to open up the cooking device nearly 88% of the time.

But chimpanzees are notoriously possessive over their food and are extremely unlikely to give it up once it's already in their possession. So the real question is whether they would attempt to use the cooking device themselves even after a raw potato was already in their hands.

This time, the chimps weren't quite as willing to wait for the food to be cooked. But a careful look at the data shows that while the chimpanzees were more likely to snack on the raw potato than in previous experiments, over time they "increased how often they placed food in the cooking device compared with eating it". Eventually, the chimpanzees learned that they, too, could cook food using the device offered to them.

They even transferred the idea onto raw carrots, showing they could apply their knowledge about the way cooking works beyond the potato slices to which they'd become accustomed. And they didn't try to "cook" pieces of wood, showing an understanding that the cooking process applied only to edible things!  

“We need not worry that chimpanzees will replace our favourite chefs, or that one day a backpacker in Africa will come across a troop of chimpanzees enjoying a barbecue while drinking a few beers.”

Of course, we need not worry that chimpanzees will replace our favourite chefs, or that one day a backpacker in Africa will come across a troop of chimpanzees enjoying a barbecue while drinking a few beers. In the wild, chimps do quite well relying on raw fruits and leaves (which gain less from cooking than do starchy tubers like potatoes), as well as termites and the occasional monkey.

What these experiments do show is that in some ways, chimpanzees have the necessary psychological machinery from which the ability to cook can quickly develop, which might suggest that our last common ancestors had those same abilities as well. "To our knowledge," write Warneken and Rosati, "this is the first evidence that [non-human] apes can plan for the future by saving food for future transformation."

But that does beg the question: if you could teach chimpanzees to control fire, would they be on their way to roasting marshmallows? Probably not, even if some populations have learned that wildfires can leave behind tasty roasted seeds. "Human cooking is generally social in nature," the researchers point out. For us, cooking is often a communal, cooperative experience ... and that creates opportunities for theft. Humans are on average more trusting of others than chimpanzees are, which may be another prerequisite for cooking to evolve. "Chimpanzees may be unwilling to engage in these behaviours when multiple chimpanzees have access to food and cooking devices, monopolising rather than sharing these resources," the researchers add. 

What Warneken and Rosati conclude from their results is that cooking may have emerged in human history shortly after our ancestors began to understand fire. Put another way, the chimpanzees' behaviour in these experiments suggests that it would only require a short leap for our ancestors to have moved from the control of fire to its exploitation. From there, it took just a few millennia of culinary tweaking to go from a roasted plant root to a delectable cheese soufflé.

The study was published in the journal Proceedings of the Royal Society B

Top header image: David C, Flickr