Natural Selection and Diseases
Natural Selection and Diseases
Cystic fibrosis, Tay-Sachs, and hypertension are three very different, yet deadly diseases. The question arises how these diseases have survived for so long. Three articles attempt to uncover the mystery behind these diseases. It has been found that there were benefits to each of these diseases, which allowed the allele to remain in the community for such a long period of time. Natural selection plays a large part in the success of these conditions.
First, cystic fibrosis has been found to be prevalent in Caucasians. It is the most fatal genetic disorder among this group. It is difficult to understand how this disease has survived for 52,000 years, especially before the development of modern medicine. The disease generally killed people before they could reproduce. In a normal situation, natural selection should have gotten rid of this defective gene; however, it did not. This suggests that cystic fibrosis may have some usefulness in society that we were unaware of until now. The author of this article suggests that those who carry the cystic fibrosis gene are protected against diarrhea. In order to understand this, it is important to know how cystic fibrosis affects the body. The gene for cystic fibrosis codes for a protein that forms channels in cell membranes. These channels funnel chloride ions out of a cell, make the surroundings saltier, and draw water out of the cell by osmosis. The fluid is useful in getting rid of unwanted debris in the lungs. For sweat glands, these channels recycle salt out of the glands and back to the skin before the salt is lost. People with cystic fibrosis have excessively salty sweat and they lack functional chloride channels. Another symptom of cystic fibrosis is thick, sticky, dry mucus clogging the lungs because the cells are not ejecting water.
Medical geneticist Xavier Estivill concluded from experiments with mice that mutations of cystic fibrosis offer some resistance to cholera and other diarrhea-inducing bacteria. Persons who are heterozygous for this gene will not have all the characteristics of an individual with cystic fibrosis, but they will have one defective gene coding for chloride channels. When the bacteria causing cholera gets into the small intestines, it releases a toxin that causes the cells to permanently open the chloride channels in...