The Man Who Went Into A Cave And Accidentally Invented An Entire Field Of Biology

What the hell happened to him?

Who was Michel Siffre?

“You have to understand, I was a geologist by training,” Michel Siffre told Cabinet magazine in 2008. Nevertheless, he admitted, “without knowing it, I […] created the field of human chronobiology.”

Siffre’s story started in 1939, in Nice, on the Mediterranean coast of France – but it wasn’t until 1962 that the events that made him famous began to unfold. Now a fresh-faced graduate of the Sorbonne, he had returned home to investigate the geological properties of a newly discovered glacier – but fate had other ideas.

“At first, my idea was to prepare a geological expedition, and to spend about fifteen days underground studying the glacier,” Siffre recalled, “but a couple of months later, I said to myself, ‘Well, fifteen days is not enough. I shall see nothing.’ So, I decided to stay two months.” 

“I decided to live like an animal, without a watch, in the dark, without knowing the time,” he said.

For 63 days, then, he lived 130 meters (427 feet) below the surface, in an icy cavern devoid of natural light or any timekeeping device. The temperature was below freezing; the humidity was 98 percent. He had no contact with the outside world.

“I had bad equipment, and just a small camp with a lot of things cramped inside,” Siffre told Cabinet. “My feet were always wet, and my body temperature got as low as 34°C (93°F).”

It was, it seems, no vacation. But it was worth it: when he returned to the surface, he brought with him a whole new area of scientific research – one significant enough that it would one day merit a Nobel Prize for Siffre’s academic successors. 

At the time, however, it wasn’t clear how important his endeavor would be: he was, after all, just a rock-licker with a weird idea for a field trip, and nobody expected the results he discovered. 

“I raised the funds myself, picked the two months arbitrarily and invented the experimental protocol,” he told New Scientist in 2018. Other scientists, he said, “thought I was mad.” 

What did Michel Siffre discover?

But what was it that so earned Siffre the ire of the scientific establishment? Not the gall of living underground for two months – it was the 1960s, after all; they were all too busy mentally torturing people (for science!) to worry about some dude in a French cave – but rather, what he learned there: that the human body had its own internal “clock”, independent of the rhythm of the Sun.

“There was a very large perturbation in my sense of time,” he told Cabinet. “My psychological time […] compressed by a factor of two.”

This was true in the short term – in psychological tests during his stay, counting to 120 took him five minutes, corresponding to an internal clock 2.5 times slower than external time – and longer term, too. “I descended into the cave on July 16 and was planning finish the experiment on September 14,” Siffre recalled. “When my surface team notified me that the day had finally arrived, I thought that it was only August 20. I believed I still had another month to spend in the cave.”

But it was perhaps most evident in Siffre’s circadian rhythm – or rather, his lack of it. Free from the time cues of clocks, schedules, and even the Sun itself, Siffre’s body lost its connection to the Earth’s 24-hour cycle, taking up for itself a longer sleep-wake cycle.

At first, his days went from 24 hours to 24.5 – but 10 years later, in a second period of cave-bound timelessness, it stretched all the way out to 48 hours.

“I would have thirty-six hours of continuous wakefulness, followed by twelve hours of sleep,” he explained. “I couldn’t tell the difference between these long days and the days that lasted just twenty-four hours.”

“I studied the diary I kept in the cave, looking cycle by cycle, but there was no evidence that I perceived those days any differently.”

He wasn’t the only one. Since his first trip underground, quite a few people have followed – some working hand-in-hand with Siffre himself – and all have reported weird, irregular, and unpredictable changes to their sleep-wake cycle. Some had 25-hour “days” followed by 12-hour “nights”; others would occasionally stay awake for three days at a time. “In 1964, the second man after me to go underground had a microphone attached to his head,” Siffre recalled. “One day he slept thirty-three hours, and we weren’t sure if he was dead.” 

“It was the first time we’d ever seen a man sleep for that long,” he told Cabinet.

Enlightenment in the darkness

Siffre faced a lot of criticism in his day – and not all of it was without merit. His style of research was flashy, people said; he was accused of being reckless with his own and others’ lives in pursuit of headline-grabbing results. Cavers and environmental scientists feared that his experiments might disturb fragile underground ecosystems, unused to the heat, light, and carbon dioxide brought by a human and his camping equipment. 

But claims that his place as a non-specialist in biology made his results dubious, or that his work was somehow trivial or unimportant, were shown to be unfounded. Siffre’s work not only kickstarted the entire field of human chronobiology – an area that today has yielded insights into issues as diverse as avoiding jet lag, gene transcription, and even how certain cancers can develop and spread.

And Siffre’s work would prove too tempting for the US and French military to ignore. “I came at the right time,” he told Cabinet. “It was the Cold War […] Not only was there a competition between the US and Russia to put men into space, but France had also just begun its nuclear submarine program. French headquarters knew nothing about how best to organize the sleep cycle of submariners.” 

“This is probably why I received so much financial support,” he added. “NASA analyzed my first experiment in 1962 and put up the money to do sophisticated mathematical analysis.”

While Siffre’s very hands-on, personal brand of experimentation is unlikely to be recreated any time soon – not least because spending lengthy amounts of time alone underground has proved distressing and injurious to just about everyone who’s tried it, Siffre included – its knock-on effects are still echoing through science today.

“Caves are a place of hope,” he said in 2008. “We go into them to find minerals and treasures, and it’s one of the last places where it is still possible to have adventures and make new discoveries.”