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Sickness: Friend or Foe?How diseases help our survival
Koh Soo-min  |  soominkoh@yonsei.ac.kr
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승인 2013.11.18  01:59:18
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THE WONDERS behind t h e existence of our life is fascinating yet profound. Most of us, at some point, have looked into the mirror and pondered where we have received the color of our eyes, the plumpness of our cheeks, or the brown shade in our hair. Although seemingly trivial, these questions touch on the very roots of evolutionary science: the existence of our life is the living collection of traits that helped our ancestors survive for thousands of generations. In order to survive, our ancestors had to be healthy and strong, thereby passing along the most useful genes for survival. We are therefore the living evidence of the Darwinian theory of evolution – the “survival of the fittest.” However, Dr. Sharon Moalem, a researcher at New York’s Mount Sinai School of Medicine, sheds light onto the completely opposite explanation. Interestingly, he claims that diseases may have been the key to helping human survival in his book The Survival of the Sickest . Is there a connection between disease and longevity? Surprisingly, some evidence seems to suggest this.
 
 

Hemochromatosis: too much iron?

 

What does the word “iron” bring to mind? Perhaps it arouses images of Ironman or the Iron Bridge, or anything else related to hardness and rigidity. It might come as a mild surprise, therefore, to learn that iron is also an essential element necessary for nearly every f u n c t i o n o f o u r b o d i l y metabolism. To begin with, it carries oxygen to our lungs via hemoglobin. It also takes part in building enzymes, detoxifying poisons, and converting food to energy. It is hard to imagine how such a fundamental element can cause any disease. But as they say, with too much of a good thing, you begin to suffer from its side effects. The same goes for iron. Too much iron in the body may cause a condition called hemochromatosis. This is a disease in which the body fails to stop iron absorption when there is already too much iron in the body. The excess iron accumulates in the body’s organs and bones, and eventually causes the person to literally rust to death. This deadly disease is genetically passed down generation to generation. But this is odd – how was a gene that may potentially cause a fatal death favoured by evolution to even exist today? In fact, a staggering number of one out of every three people of European descent carries a gene for this disease. To sum up, a lot of people carry the gene for this deadly disease, and the condition is genetically passed down. So this means that in some way, hemochromatosis must have helped our ancestors survive. How did this happen? As it turns out, hemochromatosis does not cause iron to accumulate in every storable part in the body. It causes the excess iron to concentrate only in certain parts of the body and deplete other body parts of iron. And one of the parts that become short of iron happens to be the person’s white blood cells – cells in our body responsible for fighting off disease by surrounding and devouring infectious viruses. When these iron-short white blood cells surround a virus in the body, the virus is not only isolated but it also does not have access to iron that it needs for metabol ism. In contrast, for a person without hemochromatosis whose white blood cells are loaded with iron, viruses have easy access to iron and a higher chance of survival. Untreated, hemochromatosis will ultimately rust the person to death. But i t helps fight infections that may bring death even sooner.
 
Diabetes: sugar and Slurpee* 
A staggering number of people suffer from diabetes. In fact, according to the WHO, 171 million people in the world have diabetes. This widespread disease is a condition that causes patients to suffer from unusually high levels of blood sugar, otherwise known as glucose. Glucose, l i k e iron, i s an important element for the human body. It plays a core role in fueling the brain and body metabolism and, manufacturing protein and energy. This necessary compound is stored in various parts of the body, in the muscles, fat cells, and the liver with the aid of a hormone called insulin. Diabetes is caused when there is a defect in the normal functioning of this insulin, and can bring fatal effects. High levels of blood sugar can bring rapid dehydration, and coma in extreme cases. In the long term, the patient may even suffer from a stroke, heart disease, and vascular diseases. Diabetes is again a fatal disease as much as hemochromatosis is. Then why does diabetes exist even today? It must have helped humanity survive in some way. Interestingly, the key to diabetes lies in the positive relationship between the blood sugar level and the ability to fight coldness. This is because sugar is a natural antifreeze, which means that sugar lowers the freezing point of a substance. An evidence of this can easily be seen in our everyday lives, “Slurpee” being an example. The sugar content in the drink prevents it from freezing completely to hard ice, and hence allows it to be drinkable by straw. Think of the human body as a cup of “Slurpee.” People with diabetes have higher sugar levels than those who do not. This gives the patients of diabetes the upper hand in surviving in cold area by lowering the freezing point of their blood. This genetically explains why diabetes is more common in Northern E u r o p e , a n d relatively uncommon in the hotter regions of earth such as Asia, Africa, and Latin America.
 
But are you sick?
 Although the idea that diseases might be related to longevity is intriguing, one might question how Darwin’s theory of natural selection and survival of the fittest fall into place. Kim Ji-hyun (Prof., Dept. of Systems Biology) answers this question by first defining what being sick really is. This is because the criterion with which we define “sickness” is unclear and subjective. “For example, there is a condition called ‘sicklecell anemia,’” says Kim. Sickle-cell anemia is a hereditary symptom where the shape of the red-blood cell is deformed. Unlike the normal circular shape, the shape of the red-blood cell of people who carries this condition is rigid and sickle-like. Due to the abnormal shape of the red-blood cell, the ability to transport oxygen fails. “This condition hinders a person carrying on a normal life, so we may be inclined to consider it as a sickness.” Therefore, naturally, evolution filtered and left the developed areas of the world virtually void of this condition. However, this is where it becomes interesting: over time, as evolution proceeded, sickle-cell anemia became quite rare in many parts of the world, but is relatively common among people of African ethnicity. In fact, three quarters of the global population afflicted with anemia are from the Africa. There must be a reason for this – why? It is because sicklecell anemia, which reduces red blood cells’ ability to transport oxygen, also gives a condition that increases the carriers’ immunity to malaria, a disease common in Africa. “We consider the carriers of sicklecell anemia as a sickness only in areas where malaria is uncommon.” Kim adds, “Therefore, what is normal and abnormal and what is sick and healthy are relatively defined. This means that there are no absolutely good or bad genes. There are only genes suitable for a certain environment.” Kim’s pointing out of the subjectivity of defining a sickness offers an explanation to why diseases exist even until today. Precisely the same genes that cause a certain disease may be the ones that help the survival of people in other areas of the world. This is why diseases may help mankind survive and managed to live on even until today.
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Can diseases kill us? Of course they can – and they can even be fatal in fact. But try looking at diseases through different evolutionary glasses. Some may even prove themselves to be the key to our survival.
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