Student Essay

THE NEW SCIENCE OF DARWINIAN MEDICINE

Tang Pui Ling

TWO PERSPECTIVES

There are two ways of explaining a disease. One way is concerned with how a disease arises and how it can affect the functions of the body. For example, we can say that coronary heart disease is due to the accumulation of fatty deposits in the arteries responsible for bringing oxygen-rich blood to the heart. The arteries thus become narrowed and the heart deprived of its oxygen supply. This is the proximate explanation to the disease.

But why must fatty deposits accumulate in our arteries in the first place? If we were able to metabolize fats quickly enough, perhaps such deposition will not occur. Why can't we do that? Worse, why do we still crave fried foodstuffs although we know very well that we need to check our daily fat intake? The proximate explanation offers no answers to these questions. After all, knowing what an intricate design the human body is made of, we wonder why there are apparently still flaws in it - flaws that could have been eliminated. Otherwise, we can then live in a disease-free utopia.

Another way of looking at disease is through the evolutionary viewpoint. Hopefully, this will enable us to explain why we get certain diseases and not others. The evolutionary approach, which lies in the very heart of Darwinian medicine, attempts to explain the origins of our diseases, as well as to look into the very characteristics of our design that render us susceptible to disease.

WHY OUR BODY ISN'T PERFECT

A car engineer could increase the thickness of the fuel tank to decrease the risk of fire during car collisions. However, a compromise has to be made at one point due to increased costs. Therefore, fuel tanks do rupture in some collisions and this compromise cost some lives every year.

Similarly, nature does not overspend. Perfection is not necessary, but sufficiency certainly is. As Nesse and Williams put it, "If something works well enough that its limitations do not constitute a selective force, there is no way that natural selection can improve it." Our body has the capability of dealing with certain extreme circumstances that occasionally occur. However, on certain rare occasions its capacity is exceeded and malfunctioning occurs. Therefore, there is nothing in our body that will never go wrong.

THE PROBLEM OF PAIN

Leprosy patients cannot feel pain. Isn't it good news, for who among us like that feeling? However, if you are a leper fast asleep in the countryside, you may wake up in the morning to find that a rat has chewed off part of your finger without you realizing it at all. You can walk for six hours in a pair of unsuitable shoes without realizing that you are developing blisters on your feet. By the time you realize it, the damage done is too great. So, though we may detest it, isn't pain beneficial to us after all? In other words, pain serves as a warning signal telling you that your tissues are damaged and that you need to take action or some precautionary measures to stop further damage from happening.

Fear is related to pain. Have you ever wondered why we seem to have an innate fear of snakes, heights and fire? The evolutionary explanation says that an innate fear of such things found in our ancestors was adaptive for their survival. A man who has to learn the fear of man-eating tigers only when he encounters one himself has hardly a chance to pass on his genes. But such innate, programmed fears in ourselves can be "reprogrammed", as we see how crocodile trainers stick their heads into their trainees' mouths with a bright smile on their faces.

Human beings, at least by instinct, all look forward to living in an Eden of harmony, happiness and no fear. But as long as the force of natural selection remains in our world, we are going to be disappointed, as the example above tells us. (This may incidentally also explain why there are so many whining, self-pitying individuals around.) Natural selection cares not for our comfort. It is more interested in our survival and reproductive success. Thus, if there is anything that will promote our chances of survival, it will be selected for whether we like it or not.

IRON WITHOLDING

A patient with chronic tuberculosis had low iron content in his blood. His doctor decided to give him some iron supplements to boost up his blood iron. A few days later, the patient got worse. Why?

Here are two clues for you:

1) Eggs prevent bacteria from growing on them by having lots of a protein called conalbumin in the egg white. Conalbumin binds iron.

2) Babies fed on breast milk are more resistant to infections than those fed on cow's milk. Breast milk has 20% lactoferrin while cow's milk has only 2% lactoferrin. Lactoferrin binds iron too. The answer: bacteria need iron to grow. If the body locks iron up, the bacteria will then have no access to iron and so they cannot grow. In fact, when our body gets infected, it produces something called the leukocyte endogenous mediator (LEM), which lowers blood iron content and reduces iron absorption from the gut to prevent bacteria from getting further footholds. We often tend to think that any changes in our body conditions must necessarily be bad for the body. As the above example has shown, this is not true. Sometimes, like in the above example, our body may actually be going exactly the thing it is supposed to do. The challenge for medical research right now is to find out which symptoms are beneficial for the host and what are not, so that appropriate, properly guided treatments can be made for the patients. Without adequate knowledge of such, we may unwittingly thwart our body's defense strategies, thus worsening the situation instead of helping to fight the pathogen proper.

HYGIENE

Have you wondered why we all have an aversion towards feces? Lots of parasites in our gut (e.g., flukes, and tapeworms) shed their eggs into our feces. Coming into contact with the feces of an infected host will thus render you vulnerable to parasitic infections. Your natural aversion serves you good by making you stay away from possible sources of infection.

SICKLE-CELL ANAEMIA

We have now come to a group of diseases called genetic diseases. The genes that cause diseases can be passed on from one generation to another.

Sickle-cell anemia is an example of a genetic disease. It is due to a mutation in the gene that codes for the protein hemoglobin in our body. Hemoglobin is found in our red blood cells and its function is to carry oxygen to the body tissues. Normal individuals are homozygous for the normal gene (i.e., people with two copies of the normal gene). Individuals who are homozygous for this mutant gene will get this disease. What happens is that the red blood cells will change into a crescent (sickle) shape, so that blood cannot flow properly. The person will suffer from bleeding, shortness of breath and pain in several parts of the body. Such persons usually die before reproducing.

In various parts of Africa where malaria is prevalent, it is found that the mutant gene for sickle­cell anemia is very common compared to that in other places. Many people living in these regions are heterozygotes, which means that they have one copy of the normal gene and one copy of the mutant gene in their cells. Apparently, heterozygotes have a special resistance to malaria, which the normal homozygotes do not have and yet they do not suffer from severe sickle-cell anemia as the mutant homozygotes do. Thus, in regions where malaria is prevalent, heterozygotes have an edge over both types of homozygotes. But in other regions where malaria is not a problem, heterozygotes lose out to the normal homozygotes. The sickle-cell gene thus shows how a gene can be selected for in one given environment and selected against in another different environment.

MYOPIA

Myopia, or shortsightedness, afflicts so many of us that we seldom think of it as a disease. It is, nonetheless. Besides, it is also a genetic disease. Now, if it is a genetic disease, then why has evolution by natural selection not prevented us from developing myopia? After all, it is hard to imagine how our ancestors could ever survive in the wild hunting and gathering if they could not even see clearly. A nearsighted ancestor without the benefit of a pair of spectacles would probably only make out a tiger when he is nearly becoming its food! Myopia is due to the excessive growth of the eyeball resulting in elongation. The focal point falls somewhere in front of the retina, resulting in the formation of a blurred image at the position where the retina is. Refractive lenses can shift the focal point backwards so that it falls directly on the retina itself, producing a clear image. Evidently, the growth of the eyeball must have been due to the work of a particular gene which, when activated, triggers off cell divisions along the horizontal axis o f the eyeball.

So what activates the myopic gene? And why has this gene not been selected against in the course of evolution? Our lifestyles, the reader must understand, are remarkably different from that of our ancestors. Unlike them, we spend a lot more time doing close work such as reading, writing and sitting in front of the computer for several hours a day (like what I am doing right now). Whenever we focus our eyes on something near, the surrounding objects will cast a blurred image on the retina. The regions of the retina that receive a blurred image will send a signal to the brain, which will then secrete a growth factor. This growth factor promotes expansion of the parts of the retina that receive a blurred image. Over a long time, myopia results.

Now, if you do not have a gene that effectively codes for the growth factor, you would never get myopia. On the other hand, if you do have the gene but seldom do close work, then your chances of developing myopia will also be quite small. In our ancestors' time, the gene would probably not be selected against because they seldom did close work. Thus, there were probably very few people with myopia. It seems to me that the myopic gene is also not been selected against in our modern society. This is because people with myopia can correct their vision through wearing refractive lenses or surgery. These people are fully capable of living to a ripe old age and passing on their genes to the next generation.

REGENERATION OF BODY PARTS

If a lizard can regenerate its lost tail, a starfish its lost arm, and we ourselves can regenerate skin cells and blood cells, why can't we generate a lost arm?

Imagine you are a Stone Age man. You have had a bad accident. Your brain or your heart suffers severe damage. Even if you have genes that can help you to regenerate such tissues, you would not have survived because the process of regeneration is too slow. Similarly, if you should lose your arm, you would probably have bled to death.

But how about losing a finger or a toe? You are not likely to die from that. But you can still live a long life with a finger less, so being able to regenerate a finger will not be a major advantage to you.

It is much easier and less expensive for the body to generate simple cells and tissues such as blood cells and skin tissues than whole organs or complex body structures such as the arm. The tail of a lizard and the arm of a starfish are structurally simpler than the human arm. Nature needs to weigh the inconvenience of having only one arm against the vast amount of energy and materials that the body has to put in order to regenerate such a complex structure as the arm. Besides, cells that retain the ability to divide actively throughout life may create a problem of increased risk of cancer. But if this is really so, do lizards and starfish then have a higher incidence of tail or arm cancer than if they were not able to regenerate their body parts? That is a question that we may have to look into to confirm our suspicions on whether cell totipotency will indeed increase our vulnerability to cancer.

SENESCENCE

One of my biology lecturers likes to complain about his arthritis during his lectures. "Old oredi lah," he explains, "it's like that one."

As we get older, our body will gradually deteriorate. It becomes less able to function as efficiently as before, less able to repair itself and more vulnerable to diseases. The likelihood of death also becomes greater. This process of body deterioration is known as senescence. One may wonder why the genes causing senescence have not been eliminated by natural selection. One would recall that I have mentioned earlier that natural selection does not care for our comfort, but only for our reproductive success. Therefore, there will be no selection against senescence genes if they cause harmful effects to the body only after the reproductive period of the individual is over. This is because by the time the harmful effects are manifested, many of these individuals may already have children, so their harmful genes continue to be passed on to the next generation.

Another possible reason is that genes that contribute to senescence may be advantageous to the individual earlier on in life. For example, flour beetles that reached sexual maturity earlier have shorter life spans but more offspring than those that reached sexual maturity later. The advantage of being able to have more offspring early in life may outweigh the disadvantage of having earlier senescence.

A BIOLOGICAL ARMS RACE

The world is never a safe place. An escalating arms race is always going on in the biological world between predator and prey, host and parasite. As cats start to run faster, mice are selected to run even faster so cats must run faster still. It is just like what the Red Queen said to Alice in "Alice in Wonderland". "Now here, you see, it takes all the running you can do, just to keep in the same place. "

Similarly, as we come out with drugs to combat against disease-causing bacteria, the bacteria will also evolve ways to resist the effects of the drug so that we have to come out with other ways to deal with the bacteria. For example, in 1941, staphylococcal bacteria, which commonly infect wounds, were still vulnerable to penicillin. Today, they all show some degree of resistance to the drug. Thus, we have to search for another drug against these organisms.

Actually, we are at a disadvantage in the biological arms race with our pathogens. This is because our pathogens, be it the unicellular bacteria or the multi-cellular roundworms, are much smaller and have much shorter life spans than us. An individual can have more bacterial cells living inside his intestines than the number of people on Earth. It takes most of us twenty to thirty years to produce a second generation. Roundworms take only a few weeks to reproduce themselves, bacteria mere minutes. During reproduction, gene mutations may occur and the faster the pathogen reproduces itself, the faster it can accumulate mutants within its colony. Hence, although the bacterial colony in our intestines or infected wounds may be formed from repeated cell divisions of a few "pioneer" bacterial cells, they are all not genetically identical to the "pioneer" cell from which they arise because of mutations that may occur during every cell division. In the case of staphylococcal bacteria, most of the bacterial cells were originally vulnerable to penicillin. Somehow, a few mutant cells within a colony were slightly more resistant to the drug than the rest. They were being selected for and soon, they came to dominate the colony as the rest got wiped out. Further cell divisions would bring about more mutations that might confer even greater resistance to the drug. Because of their sheer numbers and their short life cycles, these microorganisms evolved tactics to evade our defenses faster than we can do to eliminate them.

It is thus important to be careful whenever we use drugs against pathogens. Until recently, physicians often prescribed antibiotics to flu patients although antibiotics only work on bacteria and not on viruses. Their reason for doing so is to prevent flu patients from getting secondary bacterial infection that may cause diseases like pneumonia. Due to greater understanding of the process of selection of more resistant strains of pathogen, most physicians have stopped giving antibiotics unless the patient also has bacterial infection. And if one drug doesn't work, it is better to change to another drug instead of increasing its dosage, because increasing dosages will select for increasingly resistant strains. Similarly, it is best to avoid taking antibiotics on a long­term basis.

DIETARY PROBLEMS

Doughnuts fried chicken wings (especially from my hall), satay, ice cream, chocolate.... Ooh, I love them all. How sad, for I have to watch my diet. It's nightmarish to picture myself like Shen Dian Xia one day. But those delicacies, they haunt me day and night, making me feel like a miserable wretch. Why, oh why?

Recently, evolutionary biologists have come out with "absolutely splendid" excuse for my gluttony. Not that it can therefore lessen my sufferings. These people say that the reason why we tend to like sweet, salty or fried foodstuffs is that our ancestors in the past did not have as ready an access to sugars, salt and fats (or lipids) as we have now. There is more sugars in a chocolate eclair than several berries grown in nature, more oil in satay curry than can be found in seeds. Therefore, in the hunter-gatherer society in which our ancestors lived, the man/woman who could find the sweetest berries or seeds with the highest oil content would be selected for because he/she could meet his/her daily nutritional requirements. And we, fortunate souls who have ready access to plenty sugary, salty and oily foodstuffs and who do not have to move about much to look for the next meal, naturally also inherit our ancestors' preference for such foods. And unlike our ancestors, who had to gather a wide variety of foods in order to get enough nutrients for themselves, we have a much narrower diet. Thus, we are more likely to get deficiencies in certain vitamins and minerals that are often lacking in our diet. It is in my opinion that that the rising incidence of heart disease and high blood pressure may exert a selective force on individuals who prefer to eat vegetables and blander foods. It would be interesting to see if this would really happen.

MORNING SICKNESS

It makes sense to us that expectant mothers need to eat nutritious foods to nourish their developing babies. But why all these problems of morning sickness and food aversions during the first few weeks of pregnancy? Shouldn't the mother be having a good appetite instead? A study done by Margie Profet showed that during the first three months of fetal development, the fetus in the womb is especially vulnerable to toxins. This period coincides with the period of nausea and appetite loss of the mother. It seems that the nutritional requirement of the fetus during this time is not very heavy on the mother yet and so a healthy mother can afford to eat less. Usually, expectant mothers have aversions to spicy and strongly aromatic foods. Incidentally, these foods are found to contain many substances that can be toxic to the fetus. An observation made found that mothers who do not suffer from morning sickness and food aversions tend to have a higher incidence of giving birth to babies with birth defects.

JEALOUSY: AN EVOLUTIONARY ADAPTATION?

A woman blames her husband for being a philanderer. The sight of him with another woman makes her jealous. Her husband is always apologetic and swears he will never do it again. However, he never seems to mend his ways. She can put up with it no longer. A divorce seems to be the only way out.

A husband who is a philanderer is likely to spend some of his resources (e.g., time, money, and attention) on his lover(s) and possibly her children if she has any. This means that he would have fewer resources to channel to the upbringing of his wife's children. With fewer resources coming from one parent, the children's survival and well being will be affected.

Lest you be mistaken, men are not saints either. Gentlemen out there, would you allow your girlfriends or your future wives date other men beside yourself? (Unless, of course, you have some ulterior motives. For those who don't understand this, watch Woody Harrison's "Indecent Proposal".)

One interesting advantage that women have over men is that a woman can be sure that her child is hers, but a man cannot be absolutely certain about that. A man who is incapable of jealousy stands a higher risk of fathering a child not his own. It is, if you like, a waste of his resources in the sense that he has not channeled them for his own offspring. Such a man will be at an evolutionary disadvantage compared to a man that keeps his mate from other mates other than himself.

FEELINGS

I have mentioned earlier that pain, though we do not like to have it, is useful to us. Pain, as we know, is a feeling. Other kinds of feelings, such as anger, anxiety, worry, sadness and depression, are also useful to us in certain ways. This is because feelings are informative, though we may not always consciously understand them. We feel, but we do not always stop to examine our feelings. Nevertheless, our body understands them and usually responds to them by giving rise to a set of physiological and anatomical changes. Hopefully, that would benefit the individual.

The production of adrenaline by our body is greatly increased when we feel anxious, fearful or angry. Adrenaline is often coined as the "flight or fight" hormone, i.e. it helps you to either run away (presumably from some danger or threat) or to stay and demonstrate to your enemies or opponents what a superb kung-fu master you are. One of the ways in which it achieves this feat is to cause the reduction of blood flow to your gut and to your skin. Instead, it redirects your blood to the heart and the limb muscles. This is so that your heart can pump faster and send more oxygen-rich blood to the muscles that will be active during your "flight" or "fight". Suppose you get injured, less blood is also lost because less blood goes to the skin now.

Since adrenalizing is adaptive, we should be anxious or fearful or angry all the time. This is because it requires too much energy to maintain our bodies in that state all the time. Imagine your heart always beating at the rate that it does after a 100-meter dash. You'd be panting all the time!

It would seem that the best thing to do is to be anxious only when there is a real danger. The difficulty lies in deciding whether a situation is really dangerous. A rabbit seeing a fox in the vicinity will immediately make a dash to the nearest burrow. It will not stand there to see if the fox is hungry or not. Of course, there is a chance that the fox is already well fed and is not looking for food. But the rabbit will take no chances...

We may be afraid of speaking in front of a group of people, sad at the loss of someone dear to us and angry when other people stab us on our backs. Fear of becoming the center of others' attention probably stems from the fear of an intruder when surrounded by hostile stares from other animals. Sadness is usually connected to the loss of certain things that affect our reproductive success. Examples of such things are money, family, career, health, reputation and so on. Sadness stops us from our activities and makes us rethink our actions and goals. Anger can sometimes be considered as a means of intimidating one's enemies (to prevent them from antagonizing you again) and of self-defense.

I must say that it is very likely that people may tend to misunderstand (or pretend to misunderstand) these explanations about jealousy and feelings. Now that people have attributed evolutionary explanations to jealousy and anger, one wonders when they will start to justify acts like violence, adultery and murder. Religious groups may find these explanations hard to accept, even dangerous. Reasons have already been given to why stepparents tend to abuse their children - because their children are not theirs. People may start to blame their genes or their ancestors for their actions and assume no responsibility for themselves.

MY VIEWS ON DARWINIAN MEDICINE AS A WHOLE

As it is, Darwinian medicine is still at its infancy stage and thus many of its theories may have major loopholes. Personally, I think that this is inevitable. I have chosen a controversial topic for this essay, which, hopefully, will provoke some thoughts in the reader. I welcome any comments, especially counterattacks to some of the issues I have brought up. I think that this will be a very good way to refine this theory.

Reference

1. Nesse, R. M. and Williams, G. C. (1994). Why We Get Sick. Vintage Books.