LLOG 5 Webpage

Patricia Muench

2/22/09

LLOG 5: Our Flesh & Blood

1. How would you explain what “coevolution” means? Why does Carroll compare it to an “arms race”? Explain the concept in general and then offer an example from the animal kingdom.

Coevolution simply means to me that it is the explanation of two species living dependently on each other. These two species will change based on changes that each species goes through. Carroll compares it to the concept of an “arms race” because species try to keep up with new adaptations that come up by making their own changes bigger and better. The species will live in constant rotation of trying to become the more dominant species by trying to create a better characteristic. For example, Carroll uses the scenario between the newt and the garter snake. Each species changes in response to the other’s changes. The newt raises its toxicity levels to protect itself, while the snake keeps becoming more resistant to the toxicity. They live in constant rotation of these changes. Another example can be the bucket orchids and the bees. Each one changes in order to stay living in harmony with one another. The orchid will produce what the bees need, while the bees will produce what the bucket orchids need.

2. Explain in detail the hypothesis for the evolution of skin color in humans. What is the evidence offered to support this hypothesis?

Many believe that there was evolution of skin color in humans. UV Radiation is one of the main sources that support this hypothesis. In our body, there is a pigment called melanin, which is produced by a hormone in our body. When there is an increased amount of UV radiation, there is an increase in the amount of melanin production. Our bodies produce melanin as a natural way to protect our skin. This was a correlation that was discovered between scientists Nina Jablonski and George Chaplin. The type of environment relates to what our skin color will be. Evidence that supports this hypothesis includes Africans having darker skin caused by more exposure to sunlight. Then, on the other side, people in northern Europe have lighter skin because they are not exposed to as much sunlight. The Africans have been proven to have more melanin in their bodies. The body’s action of producing more melanin is a way to protect the body from harmful diseases caused by increased exposure to the UV radiation from sunlight.

3. The persistence of the sickle cell anemia mutation is considered a “classic textbook example of natural selection in humans.” Explain why this is so, including how a bad mutation is able to persist despite its ill effects.

Natural selection is a process that keeps the beneficial genes, while eventually throwing out bad genes over time from a certain species. Sickle cell anemia is considered “a classic textbook example of natural selection in humans” because the trait is considered a bad gene, but it also makes people immune to the malaria disease. A bad mutation would normally die off through natural selection, but in Africa, malaria is a disease that is affecting the whole continent. There is a persistence of the sickle cell anemia mutation because it is somewhat beneficial to Africans. Although it does cause abnormal hemoglobin, it makes a person immune to malaria. This is why sickle cell anemia has lasted so long. Malaria is a disease that is killing off many Africans. If sickle cell anemia did not cause a person to become immune to malaria, the mutation would not have lasted this long.

4. How does coevolution apply to the relationship between humans and the malaria parasite? In addition, provide another example that shows how humans and a pathogen are coevolving.

As explained previously, coevolution is when a species changes based on when another species change, both of which live dependently on each other. Malaria is a disease that is spreading quickly among humans, mostly in Africa. More and more humans are becoming darker-skinned and producing a higher level of melanin. So, as long as malaria keeps spreading quickly, the more melanin a human will keep producing. Another example of coevolution is cancer cells in humans. Society is also trying to find a cure, or at least a prevention medicine, to cancer. The drugs that humans are creating have to keep holding a higher dosage of the medicine because over time, cancer cells are becoming resistant to the medicine.

5. Using evolution concepts and math, explain why combination treatments may provide a more successful method to fight pathogens.

There has been a strong correlation between dosages of drugs and the resistance to drugs. As a drug gets stronger, the pathogens get stronger. Combination treatments will reverse this situation because as we increase the number of treatments, we will make pathogens weaker. In a stage where the pathogens become weaker, we will add another treatment. After we keep repeating this process, eventually, the pathogen will die off because it isn’t strong enough to fight off multiple treatments. This will stop coevolution because in coevolution each species changes according to the other species’ changes. So, if we create a multiple species fighting off one species, it will create too much for the one pathogen to handle.

Most Challenging Concepts

I do not really get why they consider sickle cell anemia a textbook definition of natural selection in humans. Even though there is a little bit good coming out of sickle cell anemia, wouldn’t it still eventually die off? Natural selection is something that gets rid of bad traits, not keeps them. I can understand why the disease has lived for a long time, but I do not understand why is hasn’t already died as a disease. It’s characteristics make me believe that it would not last as a disease, yet it still is living.

Seminar Questions

1. From the examples that Carroll provided, will there ever be a time where coevolution between the certain species will just stop? Do you ever think that the changes will just become too much for two species to keep living with a rotation of changes?

2. Can it be possible that combination therapy does not work? Even if there are multiple treatments, can a pathogen be strong enough to fight off every single treatment?

Connections

The newt and the garter snake can relate to the poison dart frog and the Leimadophis epinephelus snake. The newt and the poison dart frog are very similar, in the sense that they both create a poison for a defense mechanism. The garter snake and the Leimadophis epinephelus snake are very similar, in the sense that they both keep becoming resistant to the poison that their prey produces. The newt and the garter snake is an example of coevolution. Also, the poison dart frog and the Leimadophis epinephelus snake is an example of coevolution. These two scenarios both deal with species that are dependent upon one another, and they react to changes in each other.

Vocabulary Words

1. Crux: a vital, basic, decisive, or pivotal point

2. Isoleucine: amino acid required in diet; an amino acid that is an isomer of leucine and is found in most proteins

3. Efficacy: Power or capacity to produce a desired effect; effectiveness

*Definitions from www.dictionary.com*