James Farley

Underwood

12/01/07

D5

Log 6: Chapter 7- Our Flesh and Blood: Arms races, the Human Race, and Natural Selection

Synopsis:

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

The concept of coevolution is a process of natural selection that selects advantageous genes of a set number of different organisms, usually two, and develops them simultaneously. In time, each selective species in the “arms” race becomes so advanced that it is dominant over many other species within its habitat except for the other selected species that it is coevolving with. The coevolution of species enables the selected to be genetically advanced and thus, produces stronger and stronger offspring as time goes on. Caroll compares coevolution to the arms race because each selected species is adapting at the same rate as its competitor.

The case of the Oregon rough-skinned newt and the garter snake is a perfect example of the coevolutionary arms race. The newt’s selective genetic capabilities allow it to produce more and more of the poisonous chemical textrodotoxin or TTX. Over time, the newt’s poison has become so toxic that few other species can compete with its potency except its coevolutionary opponent, the garter snake. In turn, the garter snake has developed an immunity to the toxicity of the newt’s tetrodotoxin.

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

The theory of evolution of skin color in humans stems from natural selection and the process of adaption through the selection of desired genes based on the conditions of specific geographic environment. In the case of skin color, dark skin color developed in Africa to ward off the cancerous effects of the sun’s UV rays, and the diseases presented in the equatorial climate. The darker the skin, the greater survival in the environment.

            As people moved away from the equator, their skin color becomes lighter and lighter as less melanin is needed to block the UV radiation densely concentrated on the equator. This hypothesis has been examined using MR1R or melanin. MR1R is present in humans throughout the globe. The concentration of MR1R in humans indigenously becomes located farther and farther away from the equator. According to evolutionary theory, skin color has become lighter and lighter moving away from the equator because the body has adapted overtime to produce less melanin due to decreasing exposure of UV rays.

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.

Sickle cell anemia is caused by a genetic mutation in the sequences of human cells. A scientist known as Anthony Allison spend his life studying the causes and effects of sickle cell anemia. Allison hypothesized that sickle cell anemia was caused by the body’s development of a resistance to malaria.

In 1953, he was able to demonstrate that patients with the sickle cell trait were relatively resistant to induced malarial infections and that children with sickle cell harbored lower numbers of parasites than children with normal hemoglobin (Carroll 176).

The fact that sickle cell anemia has been developed over the years to build a resistance to malaria proves the cause for natural selection. In this case, the body developed a resistance that was not necessarily beneficial to itself. A resistance to malaria led to deficiencies in hemoglobin through genetic development of sickle cell anemia. Thus, a bad mutation can continue to exist despite ill effects because of its adaptive development of the genetic sequence over time.

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.

In humans, the development of the detrimental effects of sickle cell anemia evolved at the same rate as the development of malaria. As the parasite adapted to advance its chances of parasitic performance and survival, the cells of the human body coevolved with malaria and changed to combat and resist against the adaptive developments the parasite.

Another example of pathogenic-human coevolution lies in the adaptive development of HIV and the human CCR5 gene. HIV attempts to gain entrance into the bodies cells and take them over in order to further spread the virus. It is well known that some humans are immune to HIV. This immunity comes from a coevolutionary adaption in which a coding sequence in the human gene has changed to not allow the HIV virus into the cell. Thus, a coevolutionary relationship has been created from the development of HIV and the altering of the human gene sequence to protect the cells of the body from HIV entrance.

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

It is a common rule of thumb that with a single treatment, the antibody being treated will eventually adapt to the treatment and develop a resistance to the drug that it is combating. In this case, the treatment method then becomes a matter of cat and mouse as a drug is developed, the antibody develops a resistance, a new drug is made, the antibody develops a new resistance to the new drug, etc. The new method treatment involves using combination of remedies. Combination treatments lessen the adaptive evolutionary chance that an antibody will mutate to form a resistance to the multiple treatments. This type of treatment is very effective as it has been used to successfully combat HIV and malaria.

6. What is cancer? Use the ideas of mutation, selection, and time to further examine the effects and potential treatments of cancer.

Cancer is a genetic mutation within the confines of cell multiplication which causes cells to multiply uncontrollably. The uncontrollable build up of cells begins to form a tumor. In addition to the mutation in reproduction, other mutations can occur which give cells the ability to leave their original location and travel throughout the body. “As these tumors grow, additional mutations occur that may give cells the ability to leave their original location and travel to, invade, and proliferate in other body tissues (metastasis)” (Caroll 183).This process describes what actually happens in the body when referring to cancer.

In the past, the treatments developed, such as harmful drugs and radiation, were very damaging and costly to the body, as they kill both good and bad cells simultaneously. Taking into account mutation, selection and time, recently developed treatments to exploit distinct parts of the problem. “But the discovery of particular altered genes in various cancers raised the prospect of new therapies targeted at specific molecules involved in the disease, and a new generation of “rational” chemotherapeutic drugs are now being used to treat a variety of cancers” (Carroll 183). Drugs such as Gleevec specifically attach to proteins in the cancerous cells inhibit them from performing their tasks to maintain the cell. In turn, the cells die off and are unable to produce more cancerous cells. New advancements like Gleevec cause less damage to the body and are more effective in addressing the production of mutational cancerous cells.

Take Away Idea:

From this chapter, I was fascinated by the cause, effects, and development of skin tone and pigment. I never knew that melanin served as a natural sunscreen to repel harmful UV rays from the suns atmosphere. It makes sense that lighter skinned people live in colder parts of the earth and get less sunlight than dark-skinned humans living on, or relatively near, the equator. The most important concept I grasped within this reading was understanding the basics of skin color development. I found pigement extremely interesting. Science believes human kind originated from Africa, I wonder if African skin color would have developed more melanin if humans had originated in a colder more northern region instead.

Most Challenging Concepts:

            There were some challenging concepts that arose form understanding the gene sequences and new drugs used to combating against cancer. The DNA sequence found in figure 7.5 concerning evolution of mutational cancer cells and how that mutation occurred is a bit confusing. I understand it, but just looking at the diagram by itself was a difficult. As I read on, I grasped the idea as to how revolutionary treatments work. All the other concepts in the chapter were easy to comprehend and absorb. All in all, I enjoyed this chapter a lot.

A Seminar Question:

Is cancer more prevalent in humans who have less melanin or more melanin in their skin?

Communication:

An extensive amount of scientific research went into developing and understanding the human body and how it works. This study would not have been possible without clearly communicated ideas concerning the methods of research and the scientific cures and innovations developed for meeting the health-related demands of human kind and learning to fully understand the scientific problems of today’s world. Carroll is clear and effective in his speech, utilizing simple real-world concepts to illustrate broad and complex ideas in the field of genetics. The concept of the origins, changes and development of human skin tone was most clearly communicated. Understanding what cancer is and how it works is also something that I was able to take away from the reading at a basic level.

From the reading, I was better able to understand the problem rather than fear it. I was worried that I would not be able to understand the complex topics covered in this chapter. Clear communication of the ideas of the author led to the broadening of my understanding in such topics such as skin pigment, cancer mutation and overall genetic variation. Reading this chapter has taught me how to effectively communicate and convey my ideas in a clear and concise manner. I hope to take my new gained confidence and apply it to future scientific conceptual study as well as my next reading of this book.

Critical Thinking:

            The authors thoughts, ideas, claims, evidence and conclusions were all a byproduct of his ability to effectively communicate ideas through the process of critical thinking. In the chapter, critical thinking was essential to making the connection between the coevolving relationship of the Oregon rough-skinned newt and the garter snake. The illustration of these two species is a perfect example of each adapting at the same rate as the other in order to gain the natural edge for survival. Critical Thinking was further used in understanding the cause and effect of UV rays on the production of melanin in the human body, resulting in skin tone. By critically thinking, the author used examples to support his claim that variations in skin tone were dependent on geographic location and the need for the body to produce melanin to protect against harmful UV radiation from the sun.

            Critical thinking was further used to understand the nature and cause of cancer. After gaining this knowledge, critical thinking was also applied in the development of medical methods to reduce damage to the body and effectively render cancer useless in the safest means possible. Since reading this chapter, I have begun to critically think about the world around me. In day-to-day occurrence, I am always eager to understand more. I want to know why things are the way they are and I intend to find out.

Connection:

I was really able to relate to the author when comparing coevolution to an arms race. Government and international relations is my field of interest and as such, it was easy to imagine the US-Soviet build up of arms and armament. Coevolution is competitive in much the same way. Each side/species is trying to better themselves to gain an advantage over the other. Much like the US and the Soviet Union, the newt and garter snake became so advanced that no other species in their environments could compare with them other then themselves.

Vocabulary:

Plasmodium falciparum- active bacteria found in malaria

Salmonella typhi- active bacteria found in typhoid fever

Metastasis- when cells mutate and gain the ability to be mobile and invade other parts of the body which they’re not usually permitted to be in

Key Concepts:

The concept of coevolution- coevolution often causes extremes in superiorly advanced adaptations in the species that are coevolving along side each other

Origins of skin color- melanin produced to aid the body in resistance against harmful UV radiation

Coevolution is not always beneficial- example: sickle-cell anemia coevolving with malaria

Bibliography

The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution by Sean Carroll, W.W. Norton; Reprint edition (September 10, 2007)