Some of the oldest human art in Europe is completely hidden from view, tucked away in the narrow crawl spaces of deep, dark and winding caves.
To even see, let alone decorate the walls, Stone Age artists would have to crawl around with various torches, and archaeologists now suspect that all that smoke caused an altered state of consciousness.
Hallucinogenic plants have previously been associated with the otherworldly nature of cave art, but this new hypothesis suggests that ancient humans were consciously seeking a similar transformative experience in the depths of the underworld long before using other psychoactive substances.
The farther they crawled out of the fresh air, experts suggest, the greater the mental trip and the more artistic they became.
“A few years ago, when I visited some decorated caves in France, I started to notice that most of the images are found deep in very narrow caves,” said archaeologist Yafit Kedar of Tel Aviv University in Israel. The Jerusalem Post
“I started to wonder why they chose to work this way, instead of painting at the entrance of larger caves, where they could have also enjoyed natural light.”
By modeling the effect of torches and lamps on a cave’s airflow, Kedar and her colleagues have found that the narrower a cave’s entrance, the faster a human will be starved of oxygen.
In a deep cave with only one entrance, simulations show that the oxygen level can drop below 18 percent in just 15 minutes, potentially causing a state of hypoxia if the concentrations get low enough.
In humans, oxygen deprivation can naturally release dopamine in the brain, sometimes leading to drowsiness, euphoria, hallucinations or out-of-body experiences. In fact, scientists studying caves have reported experiencing similar effects even without a flaming torch in hand.
The additional use of fire makes such a condition much more likely.
In a large cave mouth with open access to the outside world, a burning flame tends to create two different layers of air: the bottom layer consists of outside air and the top layer consists of exhaust gas flowing out.
Air flow in an open cave. (Kedar et al., The Journal of Archeology, Consciousness and Culture, 2021)
In contrast, when fire burns in a narrow passage, both the top and bottom layers partially mix, meaning that air everywhere carries significantly less oxygen than the 21 percent we normally breathe.
What’s more, because oxygen atoms are lighter than carbon dioxide, they tend to float upward and descend from the tunnels of a cave to the entrance. The deeper someone travels in a cave system with a burning flame, the more likely they are to starve themselves of oxygen.
In several simulations, when ventilation was particularly limited, researchers found that oxygen levels can drop by up to 9 percent, which is about the point at which a person can lose consciousness.
This may sound like a huge deterrent, and yet hundreds of ancient cave paintings from the Upper Paleolithic, between 14,000 and 40,000 years ago, are located at very similar depths. In fact, some cave art has been found as far from the mouth of a cave as an artist could get.
For example, in the cave of Rouffignac in France, most of the ancient images are painted on the walls of extremely narrow passageways, 730 meters (about 2,400 feet) from the only entrance.
Map of Rouffignac cave with red dots representing cave art. (Dachary, Plassard & Valladas, 2016)
It therefore seems possible that some ancient people crawled deep into the dark caves of Europe to deliberately enter an altered state of consciousness. In fact, the effects of sensory deprivation, combined with the lack of oxygen, may have been the trigger for the surreal nature of their cave art.
“The images presented in such a hallucinatory state seem to float on the cave surfaces (walls, floors and ceilings) as if they form a membrane connecting the upper and lower world,” the authors explain. Kedar now hopes to test oxygen levels in actual caves to compare with the simulations.
While psychoactive plants are certainly available in Europe, evidence for their use appears in the archaeological record much later than these cave paintings.
Hypoxia, therefore, was perhaps an easier and more natural way for early humans to consciously change their state of mind, making a person feel more connected to the world around them and more expressive in their work.
The Lascaux Caves in France – home to some of the most famous paintings from the Upper Paleolithic – have even been found to leach natural gases, which could have caused a similar hallucinatory state in ancient people.
“The cave environment was conceived as both a liminal space and an ontological arena, allowing early humans to maintain their connection to the cosmos,” the authors propose.
“It was not the decoration that made the caves significant; rather, the significance of the chosen caves was the reason for their decoration.”
The study is published in The Journal of Archeology, Consciousness and Culture