Darwinian medicine, simply defined, is looking at modern medical phenomena with an evolutionary perspective. The concept is being applied to a wide variety of different maladies, syndromes, and diseases. Darwinian medicine has just begun to touch on the topic of gastrointestinal disorders. Many of the different theories and ideas of Darwinian medicine can be used to describe the origins of these disorders, and help explain their existence.

Due to the relative newness of Darwinian gastroenterology, only the five most prevalent disorders will be considered in this paper. These disorders are: gastro esophageal reflux disease, irritable bowel syndrome, peptic ulcer disease, Crohn’s disease, and ulcerative colitis. These disorders have existed since the Mayan civilizations of the Chiapas region of Mexico (Berlin, 1996). Since these diseases have existed since the ancient Mayans, the question becomes, why have these disorders not been eliminated through natural selection? Before discussing that topic, it is necessary to understand the symptoms and causes of the disorders.

Gastro esophageal reflux disease, or GERD, is a disorder that affects increasing numbers of people everyday. Often referred to plainly as "heartburn," GERD is experienced daily by approximately 10% of North Americans and monthly by about 44% (GERD, 2001). Historically, GERD was believed to be caused by the existence of excess acid in the stomach. Now, the cause of GERD is gastro esophageal motility. Gastro esophageal motility is a complex process that moves contents from one part of the GI tract to the other. When this process works backwards, and sends the stomach contents into the esophagus, GERD occurs. The term "heartburn" actually only refers to one of the symptoms of GERD. The symptoms also include acid regurgitation, chest pain, excessive belching, and bloating. Heartburn results from a dysfunction in the sphincter muscle between the esophagus and the stomach that allows acid to flow into the esophagus and irritate it. Acid regurgitation, the regurgitation of sour and bitter tasting fluids, goes hand in hand with heartburn. The acid irritates the esophagus, causing chest pain and discomfort. The excessive belching and the bloating worsen as food is consumed (GERD, 2001). Gastro esophageal reflux disease affects many people everyday. There is no cure for GERD, because physicians and researchers really have no idea what causes the dysfunction. The only possible treatment is the use of acid-reducing medications to subdue the symptoms, and in some cases, the medication is necessary for the remainder of the patient’s life.

Irritable bowel syndrome is even more poorly understood than GERD. Researchers do not even know what physiologically happens to cause IBS to occur. IBS is a syndrome, meaning that it is simply a collection of symptoms. IBS affects 20% of the population, 70% of which are women (IBS, 2001), and is the most common diagnosis made by gastroenterologists (Whitehead, 1985). The causes of the syndrome are unknown, but some hypotheses exist, none of which are generally agreed upon. The hypotheses include food allergies, stress, amount of fiber in diet, antibiotic use, GI tract infection, chronic alcohol abuse, and abnormalities in GI secretions (IBS, 2001). Not one of these causes has been widely accepted by the medical community. However, the symptoms are generally agreed upon by physicians. The symptoms are summarized into the acronym ABCD: A stands for abdominal pain, B for bloating, C for constipation, and D for diarrhea. The diarrhea and constipation are not always both present in sufferers of IBS. Usually, either one of the two is more prevalent than the other, or the two symptoms occur in an alternating sequence. IBS is characterized by irregular and painful bowel movements that are believed to be caused by irregular muscle contractions of the bowel. The severity of the abdominal pains is dependent upon the length of the bowel contractions. Bloating comes from long contractions which cut off the normal passage of air. Either the constipation or the diarrhea will be displayed in the patient, but in very rare cases, the patient will suffer from diarrhea during one onslaught of symptoms, and then constipation during another (IBS, 2001). Whether diarrhea or constipation is experienced really depends upon the individual. IBS is diagnosed when all other GI disorders have been eliminated as possibilities. IBS, like the other GI disorders discussed, is shrouded in mystery, and requires more research to uncover its true origins.

Another common GI disorder is peptic ulcer disease, or PUD. Peptic ulcers are breaks in the lining wall of either the stomach (gastric ulcers) or duodenum (duodenal ulcers) (UD, 2001). The cause of the majority of ulcers is a microbe known as Helicobacter pylori. This bacterium causes 70% of gastric ulcers, and 90% of duodenal ulcers. The bacteria reside under the protective mucous lining of the stomach and duodenum. Damage caused by these microbes triggers inflammation, which in turn causes the stomach to secrete more acid. The acid damages the protective lining exposing the defenseless stomach wall to acid and enzymes which causes the lesions to develop. Other causes of PUD are the ingestion of aspirin, ibuprofen, anti-arthritic medications, and alcohol (UD, 2001). The most noted symptom of ulcers is a burning and gnawing pain which is worst when the stomach is empty (Whitehead, 1985). Nausea and vomiting also occur, especially when the ulcer is in the pylorus, the narrowed exit of the stomach (UD, 2001). In some cases, bleeding occurs, causing the regurgitation of blood, or blood in the stool. Ulcers are very painful, and can lead to serious infections, especially ones dealing with H. pylori. PUD is quite common, occurring in about 10% of the population (Whitehead, 1985). This GI disorder at least seems to have a rational and functional cause that has been accepted by most physicians.

Crohn’s disease is an inflammatory bowel disease, a type of GI disorder that also includes Ulcerative Colitis, which completely mystifies the medical community. The cause of Crohn’s is unknown, but there has been enough research to eliminate some potential causes. This chronic illness is not pathological and unrelated to diet and allergies. The remaining hypotheses include emotional, environmental, immunological, or possibly genetic causes (CD, 2001). Crohn’s is an inflammatory process that begins under the mucous lining and spreads outward to penetrate all layers of the bowels (Whitehead, 1985). This inflammation leads to the formation of scar tissue, which can cause blockages in the intestines. The other major symptoms of Crohn’s are diarrhea, abdominal pain, weight loss, and fever (CD, 2001). Crohn’s causes the malabsorption of food which leads to the diarrhea and weight loss. The abdominal pain is due to the inflammation causing muscle spasms that occur throughout the intestines. Fever occurs as a regular defense against inflammation (CD, 2001). The major concern for sufferers of Crohn’s disease is the possibility of blockages in the intestines. Should this occur and go undetected or untreated it is possible for the whole abdominal cavity to become infected. Crohn’s disease requires long-term medical attention and treatment. Also, more research is required to identify the cause of Crohn’s disease and to discover more efficient treatments for this inflammatory bowel disease.

Ulcerative colitis is also a mystery to physicians. The newest theory for the cause of ulcerative colitis explains the cause of the disease to be an autoimmune disorder (UC, 2001). The theory states that the patient, after some injury to or infection of the gastrointestinal system, develops a reaction against his or her own bowel. Ulcerative colitis involves inflammation and ulceration of the mucous lining of the colon (Whitehead, 1985). Unlike Crohn’s disease, ulcerative colitis has very little effect on the musculature of the intestines, and therefore the amount of cramping and painful spasms of the bowel are less prevalent. The main symptoms of ulcerative colitis are blood in the bowel movement, diarrhea, and abdominal pain (Markowitz, 2001). The blood in the bowel movement results from the ulcerative lesions that form in the colon (Whitehead, 1985). The diarrhea is a secondary symptom that occurs in 80% of the cases of ulcerative colitis (UC, 2001). Abdominal pains occur in conjunction with the diarrhea. The severity of the blood loss, diarrhea, and abdominal pains can range from mild to severe. If the blood loss and diarrhea are severe, then weight loss is likely to occur. The causes of ulcerative colitis are still unclear, yet the theory for its origin is very closely linked to the idea of an evolutionary approach to medicine.

Not many researchers have applied an evolutionary style of thinking towards understanding these GI disorders. Some studies have been done, but they are few and far between. There exist some key evolutionary theories that are used to explain the origins of diseases, and why they are still existent in today’s society. One such concept is the hygiene hypothesis (Hamilton, 1998). The hygiene hypothesis, states that humans become more ill now, because they are so insistent on washing constantly and avoiding germs. The basic concept relies on the way humans’ immune system works. Paleolithic man came in contact with many more germs than that of modern man, and therefore had more antibodies and recognized more microbes, which resulted in Paleolithic man contracting fewer autoimmune and pathological illnesses. This leads to another concept that helps explains the origins of diseases. "A Paleolithic body in a modern world," this phrase explains that the human body is adapted to life in the Stone Age and not to life in modern society (Nesse, 1995). The body is equipped for hunting and gathering and getting lots of exercise; not for sitting in chairs, and staring at computer screens (Nesse, 1995). One more theory that explains the diseases of today deals with the concept of disease of civilization. With the transition from hunter gatherer societies to agricultural and urban societies came many new types of diseases and disorders. For example, obesity is a condition that was nonexistent in the Stone Age. A human unable to move quickly in that era would be at a severe disadvantage, and would have a very slim chance of survival. The basic theme of Darwinian medicine declares that the human body is ill prepared to handle the stresses of modern society.

These theories, when applied to the discussion of gastrointestinal disorders, greatly assists in their understanding. Studies are now starting to explore these theories and test them. For instance, a study involving worms and Crohn’s disease was done at the University of Iowa. The study, performed by Dr Joel Weinstock, involved the ingestion of live, sterile, parasitic worms by Crohn’s disease sufferers (BBC, 1999). The theory explains that people lived for around three million years with worms, and the immune system has adapted to them. Since humans live in a clean and mostly sterile world now, the immune system is believed to become overactive in cases of inflammatory bowel disease. The whole concept of the study was to reunite the immune system and the parasite, and see what results occur. The study was based on the aforementioned hygiene hypothesis. Only six patients participated in the study, but the experiment was so successful, that many larger studies are sure to follow. Between two to three weeks after ingesting the worms, the symptoms of the six sufferers completely disappeared and stayed away for about a month (BBC, 1999). This study brings a great amount of credibility to Darwinian medicine, and hopefully will encourage other studies of a similar structure.

Unfortunately, the other disorders have not had the same amount of luck in attracting attention and research. Some hypotheses can still be made about the origins of these disorders, and present some more readily answered questions to medical researchers. For example, examine the causes of gastro esophageal reflux disease. Gastro esophageal reflux disease is defined as a functional disorder, and the aforementioned evolutionary theories about the cause of diseases do not apply to this particular disorder. The only remaining reasonable explanation deals with the notion of design compromises. GERD symptoms originate from a faulty pyloric valve muscle that allows gastric juices to enter the esophagus. Now, how could that be advantageous to that individual? It could simplify the use of vomiting by the body as a means of expelling toxins from the stomach. Another possibility would be that the small amount of reflux used to kill dangerous microbes before they entered the stomach during the Paleolithic era. Unfortunately, no experiments have been performed, nor have any studies been published, testing these theories for the cause of GERD. The only way to determine a cause is to do further research and experimentation.

Although research needs to be done on GERD, the need is much greater for determining the cause of IBS. Irritable Bowel Syndrome is extremely mysterious, and since physicians and medical researchers have no idea about what physiologically causes IBS, it is extremely hard to pinpoint an evolutionary cause for the syndrome. The most likely explanation seems to deal with the change in dietary structure from Paleolithic man to modern man. Unfortunately, since the cause of IBS is so unclear, there does not even seem to be a way to test this theory.

Thankfully, the last disorder to discuss from an evolutionary perspective, peptic ulcer disease, seems to be more straightforward. The causes of peptic ulcer disease could also involve the hygiene hypothesis. As discussed earlier, Helicobacter pylori infections are the main cause of peptic ulcer disease. Because of the complete change in lifestyle between Paleolithic man and modern man, it is not surprising that this disease has become more prevalent. With Paleolithic man, many more microbes and parasites came into contact with the digestive system; therefore, increased production of stomach acid was practical at the time. It was another defense that helped protect the body from pathogens. On the other hand, it is possible that the increased production of stomach acid could have been the result of H. pylori manipulating the physiology of the stomach in order to eliminate all of the competition. The GI tract could have simply been the battleground between H. pylori and the human immune system. However, without some studies performed from an evolutionary perspective on PUD sufferers, all this is just speculation. Experimentation is necessary to turn speculation into fact.

Darwinian medicine brings a whole new perspective to our thought of disease. With this new approach, maybe researchers and physicians can be pointed in a new and exciting direction when looking for treatments and cures of what were once thought to be untreatable and incurable diseases and disorders. However, unless research is done and experiments performed then the true causes of these disorders will forever be a mystery, and the chances of discovering a cure will never improve. All the speculation and application of evolutionary theories is just that, speculation. Unless experiments are performed and results published, the public will forever be in a state of ignorance, and ignorance is not bliss. It is necessary to expand our frontiers and apply these new ideas to old problems, and in the end, solve them.

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Northwestern Society of Intestinal Research. "Crohn’s disease." November 25, 2001. http://www.badgut.com/pamphlets/CD.html.

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