Findings suggest chimpanzees have the intellectual abilities required for cooking, which could have an impact on our view of human evolution
A study found that chimpanzees prefer the taste of cooked food, can defer gratification while waiting for it and even choose to hoard raw vegetables if they know they will have the chance to cook them later on. The findings suggest that our earliest ancestors may have developed a taste for roast vegetables and grilled meat earlier than previously thought, potentially shifting the timeline for one of the critical transitions in human history.
Felix Warneken, a psychologist at Harvard University and co-author of the work, said: "The logic is that if we see something in chimpanzees' behaviour, our common ancestor may have possessed these traits as well. If our closest evolutionary relative possesses these skills, it suggests that once early humans were able to use and control fire they could also use it for cooking."
The transition to cooked food is widely viewed as an important evolutionary milestone because it would have allowed our primitive forebears to expand their diet and extract far more calories, reducing the amount of time required for foraging and chewing. This would have freed up time for technological ingenuity and allowed larger populations to flourish.
Previously, various animals have been shown to have a preference for cooked vegetables and meats, which are softer and easier to digest. But the suite of intellectual abilities required to make the leap to preparing cooked food had been widely thought to be limited to humans.
"What's particularly interesting about cooking is it's something we all do, but it involves a number of capacities that, even without the context of cooking, are thought to be uniquely human," said Warneken.
For safety reasons, this was a plastic lunchbox with a false bottom, which researchers used to "transform" raw sweet potato placed inside by the chimpanzees into a cooked slice of a similar size.To investigate, the scientists carried out a series of experiments at the Jane Goodall Institute's Tchimpounga Chimpanzee Sanctuary in the Democratic Republic of Congo, in which wild-born chimpanzees were given the opportunity to prepare food using a "cooking device".
"Originally we thought of setting up a camping cooker in their sleeping area, but you could imagine them getting hold of a gas tank or burning themselves," said Warneken. "This was not a viable option."
Overall, the apes chose cooked potato nearly 90% of the time when they were given a straight choice and they were nearly as keen when they had to wait one minute while it was "cooked" by the researcher (who shook the plastic box ten times). The chimps continued to opt for the cooked option 60% of the time when they had to carry the food some distance in order to place it in the "oven" - although since they often carried it in their mouths this was a challenge and they sometimes appeared to eat the food on the way, "almost by accident".
In a final display of self-control, around half the chimps chose to hoard raw potato – setting aside up to 28 slices – when they knew they would be presented with the option of cooking it later on.
"Delayed gratification is a problem for us as well," said Warneken. "We also have a tendency to nibble at food before we've finished cooking. Usually chimpanzees just eat what they can get right away and would never give up edible food, so it was remarkable to see that."
The authors argue that if the ability to cook emerged early on in our evolution, this may even have been the motivation for harnessing fire in the first place, possibly after humans had first got a taste for food prepared opportunistically on natural fires.
Richard Wrangham, an evolutionary biologist also at Harvard, agreed: "It suggests that with a little additional brainpower, australopithecines [early humans dating back 2m years ago] could indeed have found a way to use fire to cook food. I hope that this study continues to encourage archaeologists to find new way to test the prediction that I favour, which is that hominins began using fire around 2 million years ago or earlier, well before the current earliest strong evidence at 1 million years ago."
Previously, Wrangham has argued that changes in physiology of our ancestors around two million years ago, including the emergence of larger brains and smaller molars and smaller guts, mean that humans must have been cooking by this stage.
"These latest remarkable findings are certainly wholly compatible with an early origin of cooking," he added. "I see 1.8-1.9 million years ago as a time when fire control and reliance on cooked food are the only plausible explanations for the anatomical evidence of Homo erectus."
The findings place cooking as a leading candidate for why humans were motivated to control fire in the first place – alongside the benefits of warmth and protection against wild animals.
Alexandra Rosati, the study's co-author and an evolutionary biologist at Yale University, said: "The evidence from our cognitive studies suggests that, even before controlling fire, early hominins understood its benefits and could reason about the outcomes of putting food on fire."
Dr Erica van de Waal, a psychologist at the University of St Andrews, said the findings add to the growing list of parallels that have been observed between human and ape behaviours.
"The more we study our primate cousins, the more we realise that they have the bases of most of our cognitive abilities, including for language, culture and fairness," she said.
The findings are published on Wednesday in the journal Proceedings of the Royal Society B.
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