The subject of this week’s forum is Natural Selection and Evolution. These conce

Question

The subject of this week’s forum is Natural Selection and Evolution. These concepts are central to how the vast majority of biologists understand and interpret the natural world. By using the theory of Natural Selection, biologists have made incredible technological advances in agriculture and medicine. One of the goals of this class to increase your awareness of how basic principles of biology affects your life every day.

In this weeks post I would like you to research an area of medicine that our understanding of evolution and natural selection dramatically increased the understanding and treatment of a disease, pathogen (virus or bacterial) or genetic condition. Your post should provide background of the topic, describe how an understanding of the evolution and natural selection has led to greater understanding of the health condition as well as the treatments used to counteract it. You should also describe if this has improved the outcomes for individuals with your chosen condition and how it might shape the future research in this area.

If you have trouble finding a specific topic that you are interested in or a classmate has already posted on the topic you were interested in, you could explore other health related topics are also closely connected to our understanding of evolution and natural selection or Darwinian medicine. For example, the debate about the need for children’s vaccinations is still a topic that many parents don’t agree with, and the arguments both sides (for and against) use Darwinian medicine to support their claims. Which side has more validity? Another example is the “hygiene hypothesis” which states that our obsession with cleanliness has led to a dramatic increase in allergies world wide because we are not being exposed to the pathogens that strengthen our immune system.

Some websites to get you started:

http://evolution.berkeley.edu/evolibrary/article/medicine_01

http://www.sciencebasedmedicine.org/index.php/evolution-in-medicine/

http://www.pbs.org/wgbh/evolution/library/10/4/l_104_07.html

Remember if a classmate posts on the same topic you are interested in make sure you choose a different angle to explore or choose another topic.

Explanation / Answer

Natural selection is a natural process of selection of genotypes that would result in offspring with better reproductive capabilities. Natural selection is highly unpredictable and it act on pre-existing genetic variants.

Natural selection always results in better survival of organism independent of its pathogenicity. Medical treatment inhibits the process of natural selection in many of the cases.

Below are the examples showing how natural seelction favurs certain genotypes and microorganisms develop resistance:

Eg: 1. Continuous treatment of tuberculosis help to cure the disease completely as it does not offer time to bacteria to develop resistant genotype through natural selection. However, with the irregular treatment of bacteria, natural selection comes into scene, which results in the development of resistant strain.

2. The inheritance of recessive genes (disease causing) can remain prevalent if presence of two copies of an allele is disadvantageous and presence of one copy of the allele may be advantageous.

For example in case of sickle cell anaemia, two alleles may cause sickle cell anaemia but carrying one allele is advantageous in regions where malaria is common because this single copy of allele offers resistance against malaria. Thus, many people still carry the allele of sickle cell anaemia, as natural selection does not remove it; this is called “balanced polymorphism.”

Thus, people carrying one copy of sickle cell disease causing allele migrated to the regions of Africa and develops resistance to malaria parasite. They passed this protective allele to their offspring. However, two carriers with protective allele might have a child with sickle cell disease. Today, the prevalence of malaria parasite is decreased well by artificial control methods. This change in climate caused decreased number of sickle cell allele carriers.

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