Wednesday, 15 July 2009

Nature's Clock -The Rhythm of Life


For now I am looking over to biology to find out about how this filed is approaching the topic of cycles and rhythms.
Your garden tells you the time, if you look closely. First observations on biological clock in plants where made in the 4th century B.C. by Androsthenes of Thasos. He participated in the expeditions by Alexander the Great in Asia. He described the daily movement of the tamarind tree (Tamarindus indica). Its leaves move up during the day and down during the night. A similar movement can be observed in the common bean plant. (Refinetti, R., 2006. Circadian Physiology 2nd ed., Boca Raton: Taylor & Francis.)
In 1745 Carl Linnaeus, a Swedish biologist described in his Philosophia Botanica (1751) that different flower species open their flowers at different times of the day. He distinguished between three groups of flowers:

Meteorici - flowers, which change their opening and closing times according to the weather conditions.
Tropici - flowers, which change their times for opening and closing according to the length of the day.
Aequinoctales - flowers, which have fixed times for opening and closing. (Note that these are unaffected by the weather conditions.)

Only Aequinoctales are suitable for use in a flower clock. (After BBC h2g2)

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Image from Wikipedia - book cover “Systema Naturae” by Caroli Linnaei, 1760

The floral clock would be starting from 3 am with the Goatsbeard, followed by a Dwarf Morning Glory at 5 am to a Scarlet Pimpernel at around 9 am to a Day lily at 8 pm you can get flowers to open around the clock. For a full list have a look at Linneaus’ Flower Clock or on Wikipedia. The bees and many other insects must be well aware of such patterns. This might even translate into a busy working schedule inside the beehive as certain dependencies arise. Bees seem to have a clever “dance” to inform other about sources and maybe the time is an important aspect related to this communication? Anyway what I have not found so far, is a clever interpretation of why flowers only open at certain times, but maybe the insects are otherwise just too busy?
Also Michael Jackson had a floral clock on his Neverland Ranch. Although it was not a real floral clock in the sense of a biological clock, it rather is a mechanical clock decorated with flowers.
Maybe in flowers and plants you would have guessed that they respond to the rhythm of the sun, as they directly depend on it for energy and growth. Most of us would also have heard about the flowers that follow the path of the sun, such as the sunflowers, so not much of a surprise. But if looking at mammals, including humans it might come of more of a surprise that similar patterns can be studied.
The key word here is circadian clock. A definition from medterms.com “Circadian: Refers to events occurring within a 24-hour period, in the span of a full (24-hour) day, as in a circadian rhythm. Circadian rhythmicity is a fundamental property possessed by all organisms. These rhythms are driven by an internal time-keeping system: a clock. Changes in the external environment, particularly in the light-dark cycle, entrain this biologic clock. Under constant environmental conditions devoid of time cues, rhythms driven by the clock show a period near, but usually not exactly equal to, 24 hours.” The word "circadian" is a 20th-century invention. It was coined by Franz Halberger in 1959 from the Latin "circa" (around) + "diem" (a day). Halberger was the founder of modern chronobiology and the chronobiology centre and a scientist at University of Minnesota.

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Image by Franz Halberger - book cover “Introduction to Chronobiology” by Franz Halberger,1994

The circadian rhythm was in the eighties mainly studies in relation with sleep and sleep disorder. Scientist were looking at how new born babies need time to grow into the grown up cycle of sleeping at night and being awake during the day, or why teens stay up late and have difficulties getting up in the morning and why elderly people often wake up when it is still pitch black outside but can’t go back to sleep. Extended research, including experiments with people spending weeks in the dark, has shown that the daylight plays a big part in normal sleep pattern. The human body seems to be capable to sync with the light-dark rhythm of the planet. Responsible for keeping track of the time is the suprachiasmatic nuclei (SCN), a bundle of nerves located in the brain’s hypothalamus (see Kim Kiser Minn Med, Nov 2005). This region does not tell the time, it simply keeps track of it. The clock is not centralized but distributed and inherent in all cells, but is regulated to stay in sync. Steven Strogatz describes in his book Sync three different levels of sync related to the human body. The first is on the level of cells that are mutually synchronized. The next level it is the organs that stay in sync. This does not mean that they are all active at the same time, but they each keep their allocated rhythm whit in the system. As the third level Strogatz describes the synchronization between the bodies and the environment around us. On this third level he does no go into detail what this might be and how this might manifest. But logically it must have real life consequences in social space but also physical space.
A gene for the biological clock in a mouse was identified and cloned in 1997, the first such gene to be identified at the molecular level in a mammal.
New research on the circadian clock’s role in the organism suggests that the process controls almost all behaviors and physiology. In a surprising revelation, a new study suggests that the function of ALL genes in mammals is based on circadian rhythms. Up to now scientists believed that about 10 percent only are influenced by the body clock. The importance of the daily rhythm is only now uncovered.
Scientists believe that the main sync to orchestrate the vast number of independent elements that follow this rhythm is the daylight cycle. A number of studies have shown that if not exposed to the cycle of day and night, e.g. stay in the dark for a longer period of time, the sync slowly drifts off. It will automatically reestablish itself once back to exposure. (See article at the dailygalaxy)
New research has now also tried to explain the differences in life span in connection to the circadian rhythm. NYU dental professor Dr. Timothy Bromage was doing research on the growth of tooth enamel when he discovered these cycles of tooth and bone growth. The rhythm seems to vary from organism to organism and seems to have a direct impact on life span. For example, rats have a one-day interval, chimpanzees six, and humans eight. During the 37th Annual Meeting of the American Association for Dental Research, Bromage said, “The same biological rhythm that controls incremental tooth and bone growth also affects bone and body size and many metabolic processes, including heart and respiration rates. In fact, the rhythm affects an organism’s overall pace of life, and its life span. So, a rat that grows teeth and bone in one-eighth the time of a human also lives faster and dies younger.” (See article at Physorg)
A very interesting field I tapped in here and this short introduction is certainly not covering all the crucial points of circadian rhythms in biology. There is a lot more to discover especially in relation to the third level of sync as described above, where it is about the sync between bodies and the immediate or wider environment. This exactly where my UrbanDiary research should plug in. In this context I see the GPS traces, together with the mental perception of the rhythms and the geographical/physical surrounding.