Survival of The Sickest - Extra Credit-2 PDF

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Reflections on Survival of the Sickest At first glance the title of Dr. Sharon Moalem’s 2007 book, Survival of the Sickest, appears to turn Darwin’s theory of natural selection or “survival of the fittest” upside down. Instead, he provides a fuller understanding of how natural selection operates by explaining this important paradox: If evolution works by selecting traits that makes a species stronger and eliminating traits that make it weaker, why do harmful genes persist? He answers the question by tracing the evolutionary origin of such genes and showing how they have enabled species to overcome catastrophic conditions that threatened the species’ very existence. Chapter 4 entitled, “Hey, Bud, Can You Do Me a Fava”, contains some of the most interesting examples. Favism is the most common inherited enzyme deficiency carried by 400 million people around the world. People with the deficiency lack the enzyme G6PD which works to eliminate chemicals that destroy the body’s red blood cells. Destruction of red blood cells can lead to severe anemia, kidney failure, heart failure and death. Fava beans have two sugar components, vicine and convicine which when eaten produce hydrogen peroxide. If there is not enough G6PD in the body to clear out the hydrogen peroxide, the chemical will break down the body’s red blood cells. Thus, people with favism can die from eating fava beans. In spite of these serious consequences, Moalem explains that the mutation containing the G6PD deficiency persists for a very important reason. Those who carry the deficiency provide a less hospitable environment for malaria and are protected from the disease. This section of the book was of particular interest to me because it illustrated the concepts of pedigree and inherited diseases which we have studied in class. The G6PD gene is found only on the X chromosome. Since males have only one X chromosome and women have two X chromosomes, males are more likely to have the deficiency. This leads me to questions whether women are therefore more

susceptible to contracting malaria. A study which shows a breakdown of the disease by gender would be helpful to answer this question. Moalem’s discussion of the different ways that plants use toxins, including capsaicin, to protect themselves especially grabbed my attention. I have personal knowledge of the effects of the chemical capsaicin which is found in chili peppers. One of my earliest memories from when I was three years old is of finding a tube of what I thought was face cream on my grandmother’s dresser and smearing it on my lips. I will never forget the intense burning sensation and the tears and screams which followed. The tube was Capzaisin which my grandmother used to relieve her arthritis and contained the ingredient capsaicin. According to Moalem, capsaicin is a sticky poison that adheres to the mucous membranes, affects the nerve fibers that sense pain and heat and can cause the degeneration of some types of neurons in mammals. Thus, animals like rodents have learned to stay away from the toxic fruit, which gives the plant an evolutionary leg up. Moalem explains that the digestive system of mammals destroys the pepper’s seeds and does not pass through their system in the form of waste. Thus, seeds are not scattered and the chili plant does not regenerate. However, while mammals steer clear of the plant to avoid the toxin, birds do not. Birds are not affected by the toxin and more importantly their digestive systems are capable of passing the pepper seeds and scattering them to grow again. I would be interested in further research which studies the long term effects on humans who consume foods containing substances similar to capsaicin. The books suggests that capsaicin may have several beneficiary effects on humans such as stimulating endorphins, increasing the metabolic rate and alleviating pain. Are there other benefits? Moalem writes that populations who regularly consume large quantities of hot peppers tend to have higher rates of stomach cancer. Further study could show

whether there is a direct correlation between consumption of capsaicin and stomach cancer or other types of cancers. Another section of Moalem’s book which I found particularly fascinating was the story of the sheep breeding crisis in Western Australia. I have a personal interest in the estrogen like properties of plants because my mother had breast cancer which was estrogen positive. In other words, the cancer was stimulated by estrogen. Ever since her diagnosis she has avoided certain foods like soy products and yams. When I asked her why, she told me they contain substances like estrogen and she didn’t want to take the chance that eating the wrong food could trigger a reoccurrence of cancer. Moalem’s book sheds more light on this subject. He writes that in the 1940’s in Western Australia, sheep were not reproducing. They were either failing to get pregnant or having miscarriages. It was discovered that they were eating imported European clover which protects itself by producing a potent phytoestrogen that mimics the properties of the hormone estrogen. In prolonged periods of dry weather or in the arid climate of Australia the clover protects itself by producing large quantities of the phytoestrogen. This has the effect of sterilizing the sheep and limiting the number of sheep born in the next generation. Thus, the European clover is preserved. Moalem also notes that Carl Djerassi developed the birth control pill in 1951 based upon the phytoestrogen called diosgenin found in the Mexican yam. I would be interested in knowing what other plants produce phytoestrogens and how much a person must consume before it has any effect on his or her reproductive system. I think it is important for research to also confirm whether there is a link between phytoestrogens and breast cancer or other reproductive cancers. As a nursing student and future nurse I was especially interested in Moalem’s discussion of epigenetics in Chapter 7 on “Methyl Madness: Road to the Final Phenotype.” I learned from this

chapter that in caring for a patient, heath care professionals in the future will also be caring for that person’s offspring and descendants. In 2003 researchers at Duke University discovered that when they mated two fat yellow mice and gave the pregnant female prenatal vitamins, the mice produced brown skinny offspring but with DNA identical to the parents. This result happened through a process called DNA methylation. The compounds in the vitamins had attached to the gene which makes mice yellow and fat and turned off its instructions. The scientists also discovered that the brown offspring had lower rates of cancer and diabetes than their parents. Thus, the environment can affect the expression of genes without changing the genes themselves. This new discipline of epigenetics opens a world of new possibilities in medicine. While the Human Genome Project discovered all the base pairs that make up human DNA, new research is needed to identify all the possible chemical changes that can affect the expression of those genes.

Works Cited MOALEM, DR.SHARON. “SURVIVAL OF THE SICKEST .” "Survival of the Sickest : a Medical Maverick Discovers Why We Need Disease", 6 Feb. 2007....