Night turns us into alien creatures (Image: Kiril Standev/Gallery Stock)
Read more: 鈥�The night: The nocturnal journey of body and mind鈥�
THE transformation starts while you are still awake. Just before bedtime, body temperature plummets almost half a degree from its mid-evening peak. Melatonin, a sleep-promoting hormone, surges in response. Suddenly, the pressure to sleep that has built throughout the day no longer encounters the resistance of a high body temperature, and waves of fatigue assail you.
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This isn鈥檛 just your body priming you for a good night鈥檚 rest. In some ways, it is preparing you to become a whole different creature, because the night-time body has functions and a character all its own. If night never ended, we would hardly recognise what we become.
The moment you succumb to sleep鈥檚 inexorable pull, your body temperature drops. The lower body heat slows chemical reactions, setting the stage for mechanisms that mend fatigued muscles and flush toxins from the brain.
You are now ready enter an alternate reality, a rolling cascade of 90-minute sleep cycles. In each one, you pass through four stages of sleep, ending with the rapid-eye-movement phase that resembles the brain鈥檚 waking state and hosts much of your dreaming life. Then the cycle restarts. Most people are taken on this roller-coaster of phases for somewhere between 6 and 9 hours.
This is not how we used to sleep. Before ubiquitous artificial light, our sleep patterns were different. As late as the 18th century 鈥� and possibly stretching back to ancient Greece 鈥� people talked about . These two shifts between dusk and dawn were bisected by an hour or two of wakeful contemplation. By the light of a fire or a bright moon, people engaged in any number of pursuits, such as studying, writing poetry, and sex. Some evidence suggests that the practice .
As much as our sleep habits may have changed, however, sunrise has always beckoned us back to our reality as daytime creatures (see diagram).
So what would happen to us if there were no sunrise 鈥� just continual darkness for weeks on end? , where night can last three months, showed some changes, but these findings were confounded by several factors, including work schedules, which kept most natural rhythms in synch with civilisation. More satisfying answers came from a German physician called J眉rgen Aschoff, whose experiments in a disused Munich bunker in the 1960s were the first to reveal the body鈥檚 independent sleep-wake cycle in its naked state. For several weeks, Aschoff鈥檚 subjects lived in isolation, collecting their own urine and monitoring their body temperatures. Dim lights were entirely under their control, but no time information from the outside world was allowed, and when Acshoff鈥檚 staff arrived with supplies, they even randomised the stubble-length on their faces so as not to give away clues.
Out of that gloom emerged the first proof of the body鈥檚 independent clock, cementing Aschoff鈥檚 standing as a founder of chronobiology.
With no sunrise to provide external calibration, his subjects still tended to sleep for about 8 hours. However, their waking period stretched slightly beyond 16 hours, revealing an internal clock that ran 20 minutes slower than the 24-hour day. Their days settled into a pattern of about 24.3 hours. And so with each passing day, the bunker residents went to sleep later and later until they were entirely out of sync with the rhythms of German life bustling above their heads.
Aschoff鈥檚 subjects spent at most 28 days in this temporal limbo. It took a more extreme experiment to uncover just how far our rhythms can drift.
Later in the 1960s 鈥� the heyday of psychological self-experimentation 鈥� geologist Michel Siffre took a two-month solo research trip into a cave. He abandoned his watch and all other indications of external time.
Siffre had expected to end his experiment on 14 September, so he was annoyed when his support crew phoned him on what he thought was 20 August to congratulate him.
Except it wasn鈥檛 20 August. Siffre had stayed the full eight weeks underground. His subjective time, however, had passed at half the speed of the clocks outside. Siffre had made a transition to a 48-hour day 鈥� 36 hours of activity followed by 12 hours asleep. during a six-month stay in perpetual darkness in Texan caves.
How much further might we drift from 24 hours if forced to live in eternal darkness? In 2011, studies of a blind cave fish provided a clue. Phreatichthys andruzzii has evolved for 2 million years in total darkness far beneath Somalia鈥檚 deserts. With no eyes, and in the absence of any time cues, it has a circadian cycle of 47 hours ().
Could our 24-hour system actually be a subset of a more deeply ingrained 48-hour process? In a world making a full turn every 24 hours, it鈥檚 a tough question to investigate, but we can speculate on the basis of what we already know.
Each of us has our own 鈥渃hronotype鈥� on the scale of early bird to night owl. The internal rhythms of an evening person, left in total darkness for days, will depart faster from local time than those of a morning person. Their inner cycle can swell to . And yet, except for those of us working unusual shifts, we are all compelled to follow the same patterns.
Humans have conquered the seas, the skies, and even space, but the boldest occupation may have been our ventures into dark time. We have colonised the night with artificial light. Each car headlight in the darkness is like a spacesuit in a hostile environment. But conquering the night may have been a double-edged sword 鈥� far from giving us the opportunity to discover our natural-sleep persona, we are ever more removed from it.
This article appeared in print under the headline 鈥淚nto darkness鈥�
