Brilliant (32 page)

During Siffre's months underground, the scientists on the surface keeping track of his daily cycles of waking and sleeping saw that they remained quite near a 24½-hour cycle: his internal clock had not shifted, only his conscious understanding of time. But Siffre parsimoniously meted out his rations to himself, for in misunderstanding the length of his day, he believed to the last that he had weeks more to endure. At the fifty-seventh awakening—the final day of the experiment—Siffre believed it to be August 20 when, in truth, it was September 14: the time graph he'd kept lagged twenty-five days behind the actual date. "I underestimated by almost half the length of my working or waking hours; a 'day' that I estimated at seven hours actually lasted on the average fourteen hours and forty minutes," he commented after his emergence from the cave.

Siffre's experience proved that our circadian rhythm may be able to withstand the periodic absence of light, but additional research since then suggests that even small amounts of artificial light can significantly disrupt that rhythm. The effects of artificial light on sleep are particularly profound, for it is the absence of light that induces our biological clock to signal the pineal gland to increase production of the sleep-inducing hormone melatonin. Although bright lights are difficult to separate from other things that may contribute to troubled sleep—noise, coffee, busy evenings—Dr. Charles Czeisler, who conducted a study of human response to light at Brigham and Women's Hospital in Boston, found that not only intense artificial light but also long periods of lower-level artificial light can disrupt the human biological clock. As a result, the clock can be shifted by up to four or five hours, "meaning that most people in the United States are actually on Hawaii time. Instead of people experiencing a peak drive for sleep between midnight and 1
A.M.,
for most people this is now at 4
A.M.
or 5
A.M.
...[They] are forced to wake up earlier than they would like to and remain tired during the day." Dr. Czeisler notes, "Every time we turn on a light we are inadvertently taking a drug that affects how we will sleep and how we will be awake the next day."

Additionally, in modern industrial societies, humans tend to give themselves little time to wind down in darkness and quiet before attempting to go to sleep. And they no l onger vary their sleep according to seasonal changes in the length of days and nights, although even now the human biological clock still shifts according to the season and the amount of sunlight in a day. For instance, in the north temperate latitudes, the biological night is long during the winter and short during the summer, but people often bathe themselves in sixteen hours of light during all seasons of the year, as if every night fell during high summer.

Even the eight hours of uninterrupted sleep now considered desirable may be something imposed by industrial society, which requires every day of the year and all hours of the day to be divided in a certain way: now work, now relaxation, now sleep. Historian A. Roger Ekirch discovered that medieval villagers slept in a different way from modern people. Each night, they experienced divided sleep. They would go to bed soon after sundown, sleep for four or five hours—this was called "first sleep"—and then wake up an hour or two after midnight. Some people inevitably took advantage of the early-morning hours to get out of bed and work: students bent over their books; women did housework they couldn't get to during the day. Some even visited neighbors or slipped out of the house to steal firewood or rob an orchard. It was a good time for sex. But frequently people would lie quietly in bed, resting or talking, before they fell back into a lighter, dream-filled sleep—called "second sleep"—that lasted until sunrise. The quiet, free time in the small hours would have been dearly valued in a society where the days were filled with labor and obligation.

Divided sleep, Ekirch notes, began to slip away as artificial light increased. By the seventeenth century, the wealthy, who already prized their nightlife, no longer experienced it. Later, as the middle class acquired increased light, divided sleep slipped from them as well. Then laborers lost it, though vestiges of it remained even into the late nineteenth century. Robert Louis Stevenson, who sometimes slept in the open during his journey through the Cévennes in southern France, observed that a wakeful period in the middle of the night was a natural occurrence not only in people still living close to nature but in all of nature:

There is one stirring hour unknown to those who dwell in houses, when a wakeful influence goes abroad over the sleeping hemisphere, and all the outdoor world are on their feet. It is then that the cock first crows, not this time to announce the dawn, but like a cheerful watchman speeding the course of night. Cattle awake on the meadows; sheep break their fast on dewy hillsides, and change to a new lair among the ferns; and houseless men, who have lain down with the fowls, open their dim eyes and behold the beauty of the night.... At what inaudible summons, at what gentle touch of Nature are all these sleepers thus recalled in the same hour to life?...Even shepherds and old country-folk, who are deepest read in these arcana, have not a guess as to the means or purpose of this nightly resurrection. Towards two in the morning they declare the thing takes place.

Given a chance, many humans will fall back into that medieval pattern of sleep, which may have been the way even the first humans slept. When Dr. Thomas Wehr and researchers at the National Institute of Mental Health attempted to replicate prehistoric sleep conditions by imposing on a group of men a daylight time of ten hours—what people in the middle latitudes during the dead of winter experience—he found that they

slept only about an hour more than normal, but the slumber was spread over about a 12-hour period. They slept for about four to five hours early on, and another four to five hours or so toward morning, the two sleep bouts separated by several hours of quiet, distinctly nonanxious wakefulness in the middle of the night. The early evening sleep was primarily deep, slow-wave sleep and the morning episode consisted largely of REM, or rapid eye movement, sleep characterized by vivid dreams. The wakeful period, brain wave measurement indicated, resembled a state of meditation.

"We think Thomas Edison had a bigger effect on the human body clock than anyone realized," remarked Dr. Czeisler. Edison, who favored catnaps on his laboratory tables, would have loved to think so, for he once commented, "Everything which decreases the sum total of man's sleep, increases the sum total of man's capabilities. There is really no reason why men should go to bed at all." Few would now agree with Edison, for although we may not yet know why we need to sleep, most people now understand it to be essential. As researchers look more deeply into sleep, they increasingly discover the true toll its lack takes on the physiological and psychological well-being of humans. Sleep-deprived people are more prone to elevated blood pressure and blood glucose levels. Lack of sleep depresses the immune system, affects memory and brain function, and shifts levels of the hormone leptin, which controls appetite, so it may also contribute to obesity.

We humans can alleviate the way artificial light creates havoc with our biological clocks: sleep institutes, sleep programs, sleep doctors all prescribe a regimen that re-creates ancient life. In addition to advising insomniacs to get daily exercise, avoid stimulants, and slow down in the evening, experts suggest that they avoid bright light at night, go to bed in a dark room, and sleep until daylight. But other creatures adversely affected by our light can do little more than suffer its effects or adapt to it. Nocturnal animals hunting in the dark, as well as those abroad in daylight that sleep at night—standing up, or with one eye open, or in hiding—are at its mercy, and human light not only affects their circadian rhythms; it can also compromise their chances for survival and even alter their evolutionary trajectories.

As with humans, the effects of ubiquitous light on wildlife aren't always easy to isolate, since accompanying them are countless other environmental changes and losses to habitat. Buildings and roads disrupt forage routes; noise and activity compromise many animals' ability to hunt; human endeavors create new ecosystems in which artificial light plays only a part. According to William A. Montevecchi, "Offshore hydrocarbon platforms develop rapidly into artificial reefs that create marine communities. These reefs attract, concentrate and proliferate flora, crustaceans, fishes, and squids.... Lighting attracts invertebrates, fishes, and birds, and organisms at higher trophic levels are in turn attracted to lower ones as well as to the lighting."

But light alone also changes everything. For many nocturnal animals, night is a negotiation between hiding and seeing. Mammals prefer to stay in the shadows and tend to avoid the full moon, which exposes them and makes them vulnerable to predators. Artificial light not only makes it more difficult for animals to hide; it also makes it more difficult for mammals that depend on keen night vision for both food and safety to see:

Many nocturnal species are using only the rod system, and bright lighting saturates their retinas. Although many ... have a rudimentary cone system and can switch over to it within a couple of seconds, during those seconds they are blinded. Once they switch to the cone system, areas illuminated to lower levels become black, and the animal may become disoriented, unable to see the dark area...[ahead] and unwilling to flee into the unseeable shadows whence it came.... Finally, if the animal is in the lighted area long enough to saturate its rod system, it will be at a distinct disadvantage for 10–40 minutes after returning to darkness.

Light also changes the way nocturnal animals negotiate their world. A road lined with streetlights creates a kind of visual barrier: an animal cannot see beyond the lights and must take extra time, caution, and effort to make its way. One scientist, in studying the habits of pumas in southern California, observed that when a puma was "exploring new habitat for the first time, [it] stopped during the night at a lighted highway crossing its direction of travel.... In several instances, the animal would bed down until dawn, selecting a location where it could see the terrain beyond the highway after sunrise. The next evening, the puma would attempt to cross the road if wildland lay beyond or would turn back if industrial land lay beyond."

No less essential for creatures than the dark is the natural light of the night. Since light travels in straight lines, birds and mammals use celestial light for both navigation and orientation. When human light intrudes, it can misinform and confuse them. Consider the consequences of artificial light on birds. For centuries, nocturnal flyers have been drawn to lighthouses. Back when the Eddystone lighthouse keepers were eating their candles, the small light probably wasn't much bother. But a 1912 illustration shows the Eddystone lighthouse clouded by flocks of birds, milling and confused, streaming skyward, circling the white stone tower. In modern times, the dangers are multiplied: birds are drawn to the myriad illuminated windows of tall buildings and skyscrapers, and to the lights on broadcast and communication towers, which they either crash into or circle until they are exhausted. Birds also congregate around the flares on offshore oil and gas plat forms, especially "on misty and foggy nights, and as they fly near and through the flames they are burned to death." And not just elevated lights cause problems: water birds and marsh birds can mistake light-reflecting surfaces for water, and once they land on dry ground, they can't easily take off again. While they struggle to fly away, they remain exposed and vulnerable. And nocturnal seabirds that hunt for bioluminescent prey are mistakenly attracted to lights and confused by them; as a result, their search for food is frustrated. In all cases, if birds that are trapped by light manage to escape death, they've expended precious energy they can't afford to waste. For those in migration, their confusion often delays their arrival at breeding or wintering grounds.

It is not only light itself but the duration of the light that affects birds. They, too, are exhausted by sixteen-hour days. Artificial light triggers their dawn response and leads them to sing after sunset, sometimes to sing all night. The artificially extended day affects their migration and breeding patterns as well.

In the animal world, even what goes on under one streetlight after dark has complex and far-reaching consequences, for a single light is capable of changing the equilibrium of an ecosystem. Moths and insects gather around a streetlight; bats and toads come in to pick at easy prey. Notes one scientist, "The habit of feeding at artificial lights is now so common and widespread among bats that it must be considered part of the normal life habitat of many species." This not only increases the stress on insect populations; it also changes the relations between different bat species, since not all species use lights for feeding, though they may feed on similar insects. The presence of streetlights gives species that use lights a competitive advantage over other species. The non-light-using species may decline because they have lost their competitive edge. By altering habitat and spurring adaptations that might eventually become encoded in the future lives of insects, mammals, birds, and reptiles, "humans are changing the evolutionary trajectories of those affected species, causing them to adapt to new sets of conditions," notes biologist Bryant Buchanan. "Simply conserving species richness or population sizes does not conserve the evolutionary and behavioral diversity contained in those taxa."

Sometimes artificial light becomes an evolutionary trap as the age-old biological imperatives of a species, which helped it survive for eons, turn into liabilities. The most well-known example of such a trap is the predicament of the loggerhead turtle, which can live for more than 130 years. It inhabited coastal waters long before humans existed on earth, trolling the shallows, feeding on sand dollars, whelks, and conchs. The female, year after year, crawls out of the surf and onto sand beaches to nest. She has always preferred the cover of darkness for safety, and now the bright lights of shoreside developments often drive her away from prime nesting sites. When she does settle on a nesting place, she digs a pit along a sandy shore with her flippers, then deposits a clutch of eggs, falling, "as they have fallen for a hundred million years," writes David Ehrenfeld, "with the same slow cadence, always shielded from the rain or stars by the same massive bulk with the beaked head and the same large, myopic eyes rimmed with crusts of sand washed out by tears."