Humans have been building fires in the same way since the dawn of time – but until now, no one has asked why this is.
Now, Adrian Bejan, professor of mechanical engineering at Duke University, has answered this question, revealing the shape is the most energy efficient way of getting the most heat.
In his study published in Nature Scientific Reports, Bejan shows why humans "unwittingly build fires that look the same" – as tall as they are wide.
"I show that the hottest pile of burning fuel occurs when the height of the pile is roughly the same as its base diameter," he wrote. "Key is why humans of all eras have been relying on this design…heat flow from fire facilitates the movement and spreading of human mass on the globe."
His findings fit in with Construcural law, which Bejan first penned in 1996 and shows how flow systems (such as rivers or air currents) evolve to provide easier access to flows. The finding, he said, conform to these broader ideas about evolution.
"The most important aspect of this fire design explanation is that it shows why people unwittingly perform certain things," he told IBTimes UK. "We do it without thinking but we do it correctly. The fire shape is one example… making piles of stones like the pyramids of Egypt is another – it's the least construction.
"With shape of fire, the reason for that is that fire has civilised man and clearly a warm fire is better than a dead fire. That was the reason for the evolution of the fire shape in human conscious, what everybody chooses unwittingly.
"I like this word unwittingly, it says a lot not only about us, but also about scientific research – I discovered the most interesting scientific research is when I ask questions about what we consider obvious but not all of us question. Meaning we unwittingly made choices and so for me this is a very important period of happiness, as I get to talk about something everybody knows but nobody questions."
Bejan explained there are two main ways to look at the findings – either fixing the amount of fuel or the temperature needed, but both are the same shape.
He said the emergence of fire was one of a whole series of eureka moments for early humans. After discovering it, they then learned how to maintain it, then what to do with it. This knowledge was then passed down and built upon over generations.
"That's the connection between why fire shape is important well beyond the practical aspect of knowing how to make a fire to grill or in a chimney in a cold night," he said.
The importance of this discovery, in fact all of the discussion about shapes – from pyramids to fire – are about the economics. Each of us wants to live with greater ease – greater ease means less fuel if possible, less effort, more swiftly, avoiding obstacles or waiting times."
He said that we do not evolve backwards and once a good idea is out, it cannot be contained – "The occurrence of money was out of nowhere just like fire. People kept it – whatever works is kept. Then later when capital accumulation was another natural phenomenon then banks occurred and banks were kept.
"What emerged, emerged naturally – it wasn't the decision of one. It wasn't an order from above. Deep down we are discussing the physics behind evolution. It is physics which governs this phenomenon.
"We come from discovering one trick after another, this wisdom that attaches to use like scales on a fish. We've become really powerful on earth because of these things."