Who wants to live in a smoky cave?

This just in: our cave-dwelling ancestors were serious about interior design. As it turns out, they made smart spatial planning decisions when customising their quarters, positioning the hearths for their fires to optimise smoke avoidance while also allowing for a comfy chit-chat around the flames.

That’s according to a new study in Nature, in which a team of Israeli archaeologists from Tel Aviv University (TAU) developed software that models the way smoke from a campfire is dispersed in a space, and applied it to the Lazaret Cave in south-eastern France, which was inhabited by humans some 170,000-150,000 years ago.

Lazaret Cave (Grotte du Lazaret) is a major early human site of interest, an epic 40m-long cave that seems to have been occupied for tens of thousands of years, probably by Homo heidelbergensis or proto-Neanderthals.

Unnamed file
Excavations at the Lazaret Cave, France. Image credit: De Lumley, M. A. . néandertalisation (pp. 664-p). CNRS éditions.

The question of the origins of intelligent fire use and manipulation has occupied humans at least since the Greeks told of the myth of Prometheus. Nowadays archaeologists are keen to know, at what point in our evolution did humans learn to control fire and ignite it at will? And when did it become such a central feature of our social lives? 

“One focal issue in the debate is the location of hearths in caves occupied by early humans for long periods of time,” says the lead author, TAU PhD student Yafit Kedar. “Multilayered hearths have been found in many caves, indicating that fires had been lit at the same spot over many years.”

Given this long use of the same hearth, the researchers wanted to understand what might drive an early human to place their fire exactly where they did. 

“In previous studies, using a software-based model of air circulation in caves, along with a simulator of smoke dispersal in a closed space, we found that the optimal location for minimal smoke exposure in the winter was at the back of the cave,” Kedar says. “The least favourable location was the cave’s entrance.”

But that’s not what Lazaret Cave’s inhabitants did. Instead, they placed the hearth at the centre of the cave, and the researchers wanted to know why. The answer is probably fairly intuitive: these early humans would have been balancing the practicality of smoke dispersal against the central importance of the hearth for cooking and socialising. 

But, scientists being scientists, they don’t like to leave their assumptions untested. So, the researchers performed a range of smoke dispersal simulations for 16 hypothetical hearth locations inside the 290 square-metre cave. For each hypothetical hearth, they analysed smoke density throughout the cave using thousands of simulated sensors placed 50cm apart. 

In order to factor in the health impacts of smoke exposure, the team compared their measurements with the World Health Organisation’s smoke exposure recommendations. In this way, they were able to map out four activity zones for each hearth: a red zone which was unusable because of the high smoke density, a yellow area suitable for short-term occupation of just a few minutes, a green area where these early humans could have sat quite comfortably for hours, and finally a blue, smoke-free zone.

The researchers identified a 25 square-metre area in the cave that would have been optimal for placing the hearth where its human occupants could have enjoyed its communal benefits and still avoided too much exposure to smoke. And it turns out they were right on the money: that’s exactly where the Lazaret Cave-dwellers placed their fire.

Low res image 2. Jpg 2 min
Reconstruction of meat roasting on campfire at the Lazaret Cave, France. Image credit: De Lumley, M. A. . néandertalisation (pp. 664-p). CNRS éditions.

You might ask, what’s all the fuss? Why are we surprised that our early human ancestors were making smart decisions and weighing up the pay-offs? 

Well, scientists are particularly fascinated with understanding when hominins developed the kind of ingenuity and innovation that’s so characteristic of H. sapiens, the kind that allows for spatial planning, weighing up the potential future benefits of a decision, and understanding and assessing risk.

“Our study shows that early humans were able, with no sensors or simulators, to choose the perfect location for their hearth and manage the cave’s space as early as 170,000 years ago – long before the advent of modern humans in Europe,” says study co-author Ran Barkai, also from TAU.

“This ability reflects ingenuity, experience and planned action.”

Barkai also believes the modelling could help the excavators of new archaeological cave sites: “The simulation model we developed can assist archaeologists excavating new sites, enabling them to look for hearths and activity areas at their optimal locations.”

In future studies the researchers will use their model to investigate the influence of different fuel types on smoke dispersal, how the use of a cave with an active hearth varied season by season, and what the effect is of having several hearths simultaneously in a single cave.

Please login to favourite this article.