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Rhythms of Life: The Tick Tock of Our Biological Clock

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Biology 202
2006 Book Commentaries
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Rhythms of Life: The Tick Tock of Our Biological Clock

Ebony Dix

What maintains our daily rhythms – the times of day during which we are most sleepy, most productive, or have the best sex? In their book, Rhythms of Life, Russell G. Foster and Leon Kreitzman offer a great introduction to the world of biological clocks that exist in many living things, and govern rhythmic behavior in humans. The authors focus on how circadian rhythms in humans account for most of our physiological and biochemical activities. They touch upon many interesting concepts such as the idea that time is embedded in our genes and the notion that light can seriously impact circadian rhythms to the point where some individuals develop seasonal depression due to lack of light. This paper intends to discuss some of the interesting topics made by Foster and Kreitzman, while offering a critical and laudatory analysis of these topics. In addition, this paper will compare and contrast the book to specific perspectives developed in the course.

The authors begin their book with a brief synopsis of biological clocks by providing a background and definition within the context of many different organisms, including humans. Foster and Kreitzman describe that the central driving force behind the mammalian biological clock is a small cluster of cells known as suprachiasmatic nuclei (SCN), which are located in the hypothalamus of the brain. These SCN control the daily rhythms of life, which are known as circadian rhythms. One aspect of the book that deserves some praise, is the acknowledgement by the authors of the fact that the book is not a complete guide to understanding the biology of circadian rhythms, nor is meant for the 'intelligent lay reader' who has no knowledge of biology (4). They recognize that there is quite a bit of terminology used throughout that may be unfamiliar to the non-biologist. Additionally, while there is a limit to the scope of detail they include in the book, Foster and Kreitzman attempt to be "scrupulously accurate within the bounds of current understanding" (4).

In the first chapter of Rhythms of Life, Foster and Kreitzman posit that "everything we humans do shows these circadian rhythms" (11). They give the example of kidney function, which they claim is reduced at night so as to reduce urine production to prevent our sleep cycles from being blown out of phase. They also give the example of how our cognitive abilities change rhythmically over a 24-hour period, and how at the low point of the circadian cycle, the body is least resistant to cardiac and respiratory problems (12). The authors attempt to make a connection between the low point of the circadian cycle and man-made disasters. They state that it is not merely a coincidence that many of the most dramatic accidents of recent years such as Chernobyl, Three Mile Island, and Exxon Valdez all happened at night (12). This statement is problematic because the authors do not support their claim with empirical evidence to prove that such disasters were in fact the result of the careless mistakes made by sleep deprived individuals.

The second point of interest that deserves attention is Chapter 7 of Rhythms of Life, which describes a series of seemingly credible studies that were performed on Drosophila flies to prove that the molecular basis for biological clocks is coded within the genome of all living organisms. Based on the notion that the genetic blueprint of any organism lies within its DNA, experiments were performed on Drosophila flies to show that certain genes were responsible for the mechanisms of the circadian rhythm. In the mid-1950's, an American scientist named Seymour Benzer set out to first find the link between classical gene maps and the molecular mechanisms of DNA that had been discovered by Watson and Crick (98). Eventually, the series of experiments that enabled Benzer to show the correspondence between the linearity of the gene within a section of DNA, led to his search for the single gene associated with a specific behavior (99). He used observations of Drosophila flies to show that there was a genetic basis to their behavior of moving away or towards the light. Benzer observed the time-sensitive emergence of the adult Drosophila flies from its pupal case and concluded that "populations of flies had free-running rhythms of pupal emergence under constant conditions of light and temperature" (103). By observing different types of mutant Drosophila flies, Benzer and his assistant Ronald Konopka were able to identify the first clock gene tied to behavior, the period (per) gene (103). Using techniques similar to Benzer and Konopka, other groups of researchers were later able to identify new circadian mutants called the timeless (tim) gene, the Clock gene, and the Cycle gene. These genes consist of proteins that make up the biological clock of Drosophila flies. While the chapter does not go into detail about how these findings are significant to understanding the circadian rhythms of humans, Foster and Kreiztman do relate the findings to subsequent research done on mice that enabled the scientific community to draw conclusions based on the genetic similarities shared by mice and humans.

Other interesting points made by Foster and Kreitzman included the use of knowledge about circadian rhythms in humans to improve the treatment of diseases and the endurance of soldiers in the military. In Chapter 13 of Rhythms of Life, the authors offer a convincing argument that suggests certain diseases may be cured if medical professionals administer medication at the right time of day. Using malaria as the "quintessential chronobiologic disease" that is rhythmic in nature, the authors posit that medication that acts on specific stages in the life cycle of the parasites that infect the liver and red blood cells of a malaria patient can improve their "therapeutic efficacy" (213). Foster and Kreitzman also give the example of the ability of cancer treatments to destroy or inhibit the growth of rapidly dividing cells by acting at critical stages of the cell division process, such as S phase, the phase during which DNA synthesis and chromosome duplication occur. They propose that since the circadian variation in the timing of the cell cycle differs in non-cancerous cells, cancer treatments should be confined to the times of day in which lowest S-phase or DNA-synthesis activity occur in non-cancerous cells. This will reduce toxicity to the healthy cells and consequently enable the administration of higher doses of treatment to eliminate the cancerous cells (217). While the authors site an instance of successful infusion of rhythmically oscillating levels of medication to cure colon cancer in about 1,500 individuals around Europe, they don't offer any other evidence to support the idea that such treatment has been proven to be successful elsewhere for a significant portion of an infected population.

In Chapter 14, the final chapter of Rhythms of Life, Foster and Kreitzman state that research is in progress to create "a warrior who can fight 24 hours a day, seven days straight" (232). The question that this raises is whether or not sleep deprivation will have an impact on the cognitive abilities and other biological functions of these bioengineered warriors. The authors conclude this chapter by acknowledging the distinctions that must be recognized between timing and time, and that in certain instances, such as treating cancer, timing may be everything, but in times of extending our performance to fulfill some duty or goal over a short period of time, Foster and Kreitzman urge us to slow down and "look deep inside ourselves and decide whether we are sure we are going to become time-wise and not time-foolish" (243).

In general, the ideas presented by Foster and Kreitzman are in line with the main theme of the course, which deals with the concept of behavior being primarily a function of the brain. As mentioned in Rhythms of Life, the course acknowledged the ability of chemicals (drugs) to alter the brain which in turn can alter behavior. While the authors would probably agree with the idea that there are many other factors that must be taken into account when examining human behavior, such as the I-function, they seem to be focused on the concept of circadian rhythms as the driving force behind most of our actions. While the I-function and other areas of the brain were discussed at length in the course with respect to their impacts on behavior, the hypothalamus and SCN were not the focal points of the brain and behavior discussions, which seem to represent, at least according to Foster and Kreitzman, the major components of the brain responsible for our behavior. For instance, in Appendix I of Rhythms of Life, the authors provide a chart on rhythms in humans over a 24-hour period, which include the maximum and minimum levels of certain biological functions such as body temperature, gastric motility, concentration, and cardiovascular efficiency. This chart implies that circadian rhythms are the main cause of our performance, biochemistry, and physiological activities, perhaps even more than the I-function. Nevertheless, Rhythms of Life is a great starting point for those interested in gaining additional knowledge about biological clocks through different perspectives on the topic.