On pages
62-63, Dr. Moalem discusses the idea that as humanity has evolved, different
groups of humans encountered widely different circumstances, It was stated that
dense hair on the forearms and legs may have been a defense mechanism against
malaria carried by mosquitoes. This relates to Big Idea 1 (The process of
evolution drives the diversity and unity of life) because the densest hair was
generally found in the same places where malaria was most common-Italy, Greece,
and Turkey.
How does the information regarding evolutionary pressures in the book help scientists in finding out whether these evolutionary traits were beneficial? Find two more examples from the book regarding evolutionary pressures that led to positive changes in a population. Research, for one of the examples, how your pressure can lead to a positive impact for populations over time.
(Josh Baker, jbaker3@students.d125.org)
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ReplyDeleteEvolutionary pressure is “any cause that reduces reproductive success in a proportion of a population” (Yahoo), and can therefore lead to adaptation. Thus evolutionary pressure is apart of “the process of evolution (which) drives the diversity and unity of life.” In the book "Survival of the Sickest," Dr. Moalem examines traits of human populations around the globe and connects to how they could be beneficial for those living in a specific area. Likewise he also looks at what each evolutionary pressure specifically targets. For example, mosquitos who carry malaria would be more like to infect those with more skin exposure. Thus Dr. Moalem was able to make the connection that dense leg hair probably warded off mosquitos, so that is how the selective trait became prevalent in mosquito infected societies. According to our class flowchart, the leg hair would be the “selective advantage,” and “over time” the population would “adapt” and acquire the leg hair trait.
Another evolutionary pressure that was talked about was lack of salt in African American populations transported to America. Those who were able to retain salt in their bodies were selected for, and therefore able to live through the journey to America. In effect though, the increase levels of salt in the blood complimented high reactivity of salt; hypertension had its onset. Though hypertension is regarded negatively now, in the African American population of the colonial time period, it proved beneficial.
On page 69 Dr. Moalem talks about the gene CCR5- Δ32. This gene is known to protect 5 to 10 percent of the Caucasian population from AIDS, but originally this favorable variation was selected for to protect humans from hemochromatosis. Hemochromatosis according to both Dr. Moalem and the Mayo Clinic is a disease in which access iron is stored in the vital organs. Although the gene is not very prevalent, it could possibly be once again selected for in a population largely infected with AIDS, like in Africa. An article called “HIV: the ultimate evolver” confirms that HIV/AIDS “responds to selection pressures quickly” and can henceforth become resistant to many of the antiviral drugs (Berkeley University). The gene prevents the virus from multiplying, and prevents the necessity of any drugs.
Ideally fallowing our evolutionary flow chart, those with the anti-HIV gene will be faced with the environmental pressure (AIDS), have a favorable variation (CCR5- Δ32) and over a long period of time the population could adopt the change in allele and help future populations survive and reproduce. It would be very interesting to see the insertion of the CCR5- Δ32 gene into all human DNA in the near future with the help of genetic mapping projects (like the one Sam Rhine talked about) and genetic engineering, This way people will be immune to the HIV virus. Either way CCR5- Δ32 can lead to a positive impact for populations over time, and in the near future.
Posted by Madeline Merageas, mmerage4@students.d125.org