Discusses human measurement of time and perception of time through the ages.
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EMPIRES OF TIMECALENDARS, CLOCKS, AND CULTURES
By ANTHONY AVENI
UNIVERSITY PRESS OF COLORADOCopyright © 2002 Anthony Aveni
All right reserved.
Chapter OneTHE BASIC RHYTHMS
First the tide rushes in, plants a kiss on the shore, Then rolls out to sea and the sea is very still once more. -"Ebb Tide"
Metaphor is a figure of speech by which the meaning of one word is transferred to another. Our era is dominated by computer and mechanical metaphors. We use terms like network, input, feedback, gridlock, and information flow to describe social situations and interactions as if to imply that society is a system that functions according to the laws of physics. But in the lyrics above from a popular song of the 1950s, the tide becomes the metaphor to describe the love one person experiences for another. Like our emotions, the tide waxes and wanes from one extreme to another. Or, is it like the feeling of being torn apart by circumstances after coming together? For artists and poets, the changeability of human feelings finds expression in the way the waters rise and fall, not just over a day, but even from moment to moment, for the beat of each wave that breaks upon the shore imitates inmicrocosm the slower rhythm of ebb and flow that makes up the eternal tidal harmony.
TRACKING DOWN THE SENSE OF TIME
I am engaging in this romantic talk to show that we use nature's behavior as a model to describe something we feel. In the passage from that old song, we feel time not only as an endless flow of metronomic beats but also as a kind of rhythmic surge, a recurring pattern we can trace to our very roots, to an age before we could even call ourselves human beings-when we came out of the sea.
It is well-known that the life cycles of marine organisms respond to the ebb and flow of the tides. The periodic inundation and exposure that results from tidal flow controls changes in temperature, pressure, agitation, salinity, and feeding conditions. Take oysters. When the sea is high, they open their shells for a longer period of time than when it is low: not much longer-it is too dangerous; only 3 or 4 minutes more per hour. Just enough longer to take safe advantage of the fresh source of nourishment brought in by the turning of the tide.
In the early 1950s, biologists pulled about a dozen oysters from New Haven harbor and shipped them to Northwestern University in Illinois for study. The oysters were submerged in their original harbor water and kept in total darkness. To explore their feeding patterns, the researchers tied to the shells fine threads that could activate recording pens every time the oysters' muscular movements caused the hinged shells to part or come together. Just as expected, the oysters continued to open and shut their shells as if they still were snug on the bottom of their home harbor, even though they had been displaced to another time zone more than a thousand miles to the west. Then, after about 2 weeks, something strange happened. Gradually the hour of maximal opening of the shells began to drift from day to day. Now, anyone who lives near the shore knows that the high- and low-water marks shift gradually from day to day. Tides are synchronized not with the place of the sun in the sky; rather it is the moon's schedule of appearance that matters, and the moon runs about 50 minutes, or eight-tenths of an hour, later than the sun's cycle. On the average, successive high and low tides occur nearly an hour later each day. We would expect all oysters to open and shut on a 24.8-hour schedule. But, the biologists in Illinois were witnessing a daily drift that corresponded to a different beat. After four weeks of recording and analyzing the data, they had determined beyond any doubt that the oysters had restabilized the rhythmic opening and closing of their shells to the tidal cycle that would occur in Evanston, Illinois, had there been an ocean in that location. For the rest of the time the oysters were observed, they continued to maintain this new cycle (figure 1.1). It was as if they had gradually adjusted their life's pace to correspond to the time when the moon was overhead as seen from Northwestern University rather than from New Haven harbor. Could this lowly form of life actually feel the moon's presence through the sealed walls of the laboratory? (Think of that the next time you start to douse a plate of oysters with the stinging pungency of a few drops of Louisiana hot sauce!)
If you are impressed with the sagacity of a brood of New England mollusks, consider the even lowlier potato. Experimental biologists have charted its metabolism by measuring the rate at which it uses oxygen. They removed the sprouting eyes of potatoes and placed them in hermetically sealed containers shielded from outside fluctuations in temperature, pressure, humidity, and light intensity. But the deprived spuds kept the same rhythmic cycles they had before they were snatched out of their natural environment. Peak consumption of oxygen occurred at 7 A.M., noon, and 6 P.M. every day. And when the unseen sun was gone from the sky, oxygen consumption fell to the standard nighttime low. There were annual changes, too. When it was summertime outside the container, the noontime peak was lessened; and in wintertime, it became enhanced.
As insignificant a link as it may seem in the great chain of being, a blindfolded potato still knows not only the time of day but also the season of the year! Furthermore, the rates of potato metabolism were found to correspond to the barometric pressure outside the containers in a most unusual way: they indicated what the barometer read, both yesterday and the day after tomorrow. While we can understand that yesterday's pressure changes might make for alterations in humidity and temperature that can be connected in turn to today's oxygen consumption, it is difficult to comprehend just how information can be conveyed to an imprisoned potato that enables it to adjust the height of its noontime oxygen consumption peak by just the correct amount to correspond to the barometric pressure two days later. A meteorologist removed from his usual post in front of a TV weather map and sealed away in a container could hardly be expected to do as well in predicting the weather.
Of all the rhythmic time cycles in biological organisms, those of the honeybee probably are the most well-known and certainly among the most elaborate. Like many other scientists, the German biologist Karl von Frisch initiated his studies, back in the 1930s, quite by accident. One of his colleagues told him that whenever he breakfasted on his terrace, he noticed that the bees seemed always to be there at the right time to anticipate the savory taste of the jams and marmalades that often were set out. They showed up whether or not sweets were at the table. How could a bee acquire this punctuality? Was there within itself, a sort of built-in clock that goes off at the right hour, or did the insect receive clues from the outside environment?
To try to find the answer, von Frisch set up a series of experiments. Food sources were set out in different directions at different times of the day. When bees coming straight out of the hive darted immediately to the food source, it became clear that somehow information about the location of that source was being transferred back to the hive by incoming members of the bee community. Peering inside the hive, von Frisch discovered that the transfer mechanism was a kind of round dance performed by a foraging bee shortly after it arrived back at the hive to dump a load of nectar. It would dance rapidly in a narrow circle, completing half a course in a clockwise direction, then would run along the diameter, and finally complete the other half loop in a counterclockwise sense-a sort of figure eight (figure 1.2). As the bee danced, spectators tagged along after it in great excitement, touching the tip of its wiggling abdomen with their feelers as they went. Cleaning itself off, the forager-communicator then left the hive and returned directly to the food source, only to be joined moments later by attentive comrades.
What information had been conveyed through this curious round dance? How did the bees watching the dance know where to proceed? These questions continued to puzzle von Frisch and his co-workers for a long time. Surely, it was not the sense of smell that caused the bees to arrive at their target, for they showed up regardless of whether the experimenters laid out honey or sugar water. And the bees certainly could not see the dancer perform, for the comb on which all the action took place was sealed away in darkness. Any information about orientation must have been picked up by other means-for example, by touch, inside the hive. The experiments continued.
When von Frisch varied the distance to the feeding place, he discovered that the farther away the source, the longer the dancing bee took to complete a dance loop-from forty runs a minute for a source just a few hundred meters away, down to just a few turns a minute for a feeding place situated several kilometers from the hive. And, if the source was nearby, the communicator-bee seemed to wag its abdomen much more rapidly during the straight diametrical portion of the dance. Did this action reflect that the dancer had consumed more energy when running a long way from the hive? Perhaps a tired bee automatically conveys information about the distance to a food source because it has less energy in reserve and consequently performs a much slower dance. But what about direction? If the companion bees know how far to fly, how do they know which way to take off?
This information is conveyed in a most remarkable way. Actually the bees were navigating by the sun. Von Frisch discovered they had developed a brilliant way of measuring the angle between the food source and the sun as projected from the hive. On a horizontal comb surface, the angle between the straight portion of the dance and the bearing of the sun is the same as the direction between the sun and the source as seen from the hive. In other words, if a food source lies 40 degrees to the left of the sun as viewed from the hive, then the bee conducts the straight portion of its dance at a 40- degree angle to the left of the direction of the sun, which, it will be remembered, cannot actually be seen from the dance floor. What if the comb surface is vertical? Then the forager bee performs the dance so that the angle to the food source is measured from the vertical instead of from the direction to the sun. In our example, the straight portion of the bee's dance would be 40 degrees east of vertical. Von Frisch could not fool the bees by changing the orientation of either the nectar or the hive. They always made a "beeline" directly to the feeding place once informed about direction and distance via the wagging dance.
If bees know when to turn up at a feeding place, they must possess some sense of time. And, because they convey information by marking off the angle of the sun, it would appear likely that they are cued in to this timing sense directly by the sun. The bee learns that when the rays of the sun arrive from certain portions in the sky, it is time to forage. Von Frisch even trained his bees to become attuned to several different foraging times each day. But this idea of environmental cueing has its problems, for bees, like potatoes, when totally isolated from all outside periodic changes, continued to behave the same way. They appeared at a feeding spot at the time of day for which they had been trained, even when they were exposed to constant artificial light, temperature, and humidity. After years of experimentation with time sensing in the honeybee, von Frisch concluded that "we are dealing here with beings who, seemingly without needing a clock, possess a memory for time, dependent neither on a feeling of hunger nor an appreciation of the sun's position, and which, like our own appreciation of time, seems to defy any further analysis."
We can say the same of potatoes that adjust to the forthcoming barometric pressure and of oysters that manage to convince themselves that they live in a nonexistent ocean just west of Chicago. But where is the elusive rhythmic clock for which von Frisch was searching?
Cycles of about a day's length possessed by nearly all living organisms are called circadian rhythms (from the Latin circa, "about," and dies, "day") and have been recognized in Western culture at least since the time of Aristotle. Twenty-four centuries ago, he observed that certain plants raised and lowered their leaves on a regular day-night schedule. But it was not until the age of controlled scientific experimentation (22 centuries later) that we began to probe the detailed nature of this biological clockwork. In 1729, the French scientist Jean de Mairan conducted the first controlled light-dark experiment on plants in a laboratory. He found that the daily periodic oscillations of plant leaves persisted even when the plants were isolated from the natural environment. This so-called de Mairan phenomenon has been observed in practically all living forms from humans down to one-celled organisms. In all cases, the cycle is close to, but never precisely the same as the earth's rotation period (generally it varies between 23 and 27 hours for different kinds of organism). Furthermore, most subjects can be trained after several days to adapt to a new artificial period through environmental control.
Mice are particularly cooperative. Biologists have weaned them away from their normal morning activity of running on a wheel by subjecting them to a single hour of artificial daylight and then keeping them in the dark for the remaining 23 hours of the day. As the graph in figure 1.3 shows, after several days of such exposure, the mice adopted a routine: they would always run the wheel immediately after the hour of exposure to the light. After several weeks, the mice were allowed to "run free": that is, they were taken out of the artificial periodic environment and kept in darkness all the time. Under these conditions, wheel-running activity often persisted for several days and occurred at the same time of day to which the mice had become "entrained," to use the biologists' terminology; but then the mice began to become "disentrained," and their activity period drifted slowly toward times slightly earlier in the day. This free-running rhythm had a shortened but astonishingly precise period of 23.5 hours. (Notice the straight sloped line in figure 1.3 that fits the time of initiation of wheel activity from the 60th day forward.) Also, the length of time the mice spent running in the wheel became a little bit longer during this stage of the experiment. After 90 days, the biologists tried to switch the mice to a new period by exposing them to light 18 out of 24 hours per day. Released to run free after the 130th day, the mice were active for longer intervals; nevertheless, they kept to a rhythmic cycle that once again corresponded precisely to something less than a day. These experiments not only demonstrate the complicated nature of circadian rhythms, they also raise a fundamental question: Is a sense of time built into all organisms, or are we really being driven by the earth clock outside us?
In our world, there is little to be gained by marching to the tune of a different drummer. Little wonder that most biological rhythms are virtual duplicates of nature's basic periods-the day, month, and year, all of which have their celestial origins in the rotation of the earth and the movement of the sun and the moon. To rephrase my question: How is the connection between life cycles and celestial rhythm established? One theory, the hypothesis of the internal timer (or the endogenous hypothesis), suggests that because these rhythms persist when the organism is deprived of functioning within the natural environment, every piece of living matter must be its own timer. In other words, every living thing has the capacity to develop its own internal, chemically based timing system. This idea makes good sense because the theory of evolution teaches that the mechanisms of natural selection favor the survival of the organism that achieves an adaptive advantage. Having evolved over millions of years, the oysters that "know" when to keep their mouths shut (or open) get fed; the rest become losers. Every successful class of organism needs to inherit and further develop an accurate biological clock so that it can know when to anticipate environmental change better than its competitors.
Excerpted from EMPIRES OF TIME by ANTHONY AVENI Copyright © 2002 by Anthony Aveni . Excerpted by permission.
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