Ancient Sous-vide: is cooking in hot springs repeating the behaviour of our ancestors?

Grand Prismatic Spring Overlook, Yellowstone National Park via Wikipedia Commons

On August 7th, 2020, two cousins, a neighbour and their families decided to cook two whole chickens in a hot spring at Shoshone Geyser Basin, in Yellowstone National Park. That following November, three of these imaginative chefs were sentenced to two years’ probation, banned from the park for that period and fined between $500 and $1,200, according to court documents for violating laws governing the use of Yellowstone National Park. Along with being illegal, it is extremely dangerous to stray from premarked paths in Yellowstone, let alone romp around near a hot spring. Water in the park’s hydrothermal systems can exceed 400 degrees Fahrenheit (205℃), a temperature too hot to even bake a chocolate chip cookie, and can cause severe or fatal burns. 

Fisherman cooking a recent catch in Fishing Cone geyser, West Thumb Geyser Basin, Yellowstone National Park, unknown date via Wikipedia Commons

While seemingly a bizarre, possibly comical idea to cook chickens in a hot spring in 2020, it may not be a novel idea; instead, this practice may not be well understood or documented. People have been travelling through and inhabited the region which is now Yellowstone for more than 11,000 years as indicated by archaeological evidence. Unfortunately for us, however, evidence for many human behaviours, such as cooking in a hot spring, do not preserve in the archaeological record. We may never know if this practice has any continuity. In 1870 while exploring the region of northwestern Wyoming which would later become Yellowstone National Park, the Washburn Expedition wrote about a man fishing in Yellowstone lake near the West Thumb Geyser Basin who caught a trout and swung it ashore. The trout fell into a nearby spring and was boiled almost instantly. Later visitors of the park imitated this stunt, catching fish from the lake and cooking them directly on the hook in the adjacent hot spring, then appropriately referred to as Fishermans Kettle, Fishing Pot Hot Springs or its current name, Fishing Cone. This activity became so popular that in 1903 a national magazine declared that no visit to the park was complete without the experience. The practise has since been prohibited. 

While seemingly innovative, our ancestors might have developed this cooking method long ago. A recent article in PNAS (Sistiaga et al. 2020) from a team of researchers from the Summons lab at MIT and the University of Alcalá has discovered evidence that hot springs may have existed in Olduvai Gorge. One of the worlds most important paleoanthropological sites, Olduvai Gorge is located in the Great Rift Valley in Tanzania where early human ancestors were thought to have existed 1.8 million years ago. The Great Rift Valley is a series of contiguous geographic trenches in eastern Africa which are the result of Earth’s tectonic plates moving apart. This plate shifting causes increased volcanic activity in the region, making the presence of hot springs here conceivable. Olduvai Gorge is significant in exhibiting evidence for early stone tool production, highlighting the increasing developmental and societal complexities in early human ancestors. 

In sediment samples from the site, assemblages of bacterial lipids which are unambiguously indicative of high-temperature water were identified through high-performance liquid chromatography, a technique used for the separation and characterisation of complex mixtures of organic compounds. Lipids such as these, which can be traced back to their natural source organism in the environment, are known as biomarkers, and they are sought-after by organic geochemists seeking to reconstruct past environments. Interestingly, these lipid biomarkers found at Olduvai Gorge are the same lipids that are produced by a modern bacteria that the Summons lab previously studied from hot springs of Yellowstone National Park itself. This type of environmental reconstruction is important for many archaeologists and paleoanthropologists studying relationships and interactions between past people and the environment they lived in. 

Hydrothermal circulation near sites that were considerably utilised by early hominins may have influenced their actions and proved advantageous. Sistiaga et al. 2020 suggest this environment might have been auspicious to early hominins looking to use hot springs for cooking. Understanding early cooking practices such as this is vital in paleoanthropology. Early human ancestors experienced an unprecedented increase in brain size 1.8 million years ago, and an increased caloric intake was required to power it. Many anthropologists believe this calorie deficit was made up through a combination of increased meat consumption and cooking. Cooking breaks down collagen in meat and softens plants, releasing their stores of starches and fats, helping the digestive system expend less energy processing them and extracting more energy from the food itself. This change in behaviour is often discussed in terms of early Hominin fire use, but this recent work at Olduvai Gorge may shed light on other creative ways our ancestors procured their extra energy. 

Exact details on how humans might have cooked with hot springs are still up for debate. Dr. Sistiaga mentions “we can prove in other sites that maybe hot springs were present, but we would still lack evidence of how humans interacted with them. That’s a question of behaviour, and understanding the behaviour of extinct species almost 2 million years ago is very difficult” (MIT News Office). This act might have been intentional, including boiling meat, roots and tubers or opportunistic, with early hominins scavenging animals who fell into hot springs and were slowly cooked. 

Even if it might have been a precursor to cooking with fire and accelerated human evolution, cooking in Yellowstone’s geothermal baths is dangerous and illegal because it requires walking across thin crusts above the water. Human fatalities from falling into thermal features in Yellowstone National Park is not abnormal and have occurred as early as the opening of the park. Hot springs at Yellowstone also host specially adapted mats of micro-organisms called thermophiles; single-celled organisms including types of bacteria that thrive at incredibly high temperatures. These life forms are fragile and require specific water chemistry to thrive and provide hot springs with their unique colour schemes. Introducing any foreign matter into a geothermal feature can destroy the specific environment these organisms inhabit. In an interview with the New York Times, the culinarians said they wouldn’t try what they did again at Yellowstone. However, as far as their chicken goes from their experiment on August 7th, they claimed, “It was fantastic”.

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Jennifer Keute

Jennifer Keute is a DPhil student in archaeological science at the University of Oxford. Her research focuses on using chemical methods to analyse organic material from the archaeological record including food, resins, and cosmetics.
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