On page 63, Dr. Sharon Moalem talks about adaptation to disease
(specifically malaria) and how humans near high counts of malaria tend to have
the densest hair. He thus makes connections to the first AP biology big idea, that
“the process of evolution drives the diversity and unity of life.”
However, why are Africans not prone to
dense leg and arm hair, since they were and are highly exposed to malaria. What other diseases are they prone to in order to
protect them from Malaria? What harmful effects could dense hair have on human
populations in areas with high cases of malaria, and what protection to malaria
does having dense hair offer? If malaria is not as common today, why is dense
hair still prevalent in Mediterranean areas, is such a trait expected to phase
out of populations? Use scientific terms from the evolutionary unit to answer
the preceding questions. In addition please provide an example of a similar disease in which two separate adaptations arise based on geographical location.
Madeline Merageas (mmerage4@students.d125.org)
Dr. Sharon Moalem brings the Big Idea 1 that “the process of evolution drives the diversity and unity of life” into perspective when certain environmental pressures causes a change in populations. Specifically, Dr. Moalem talks about the relationship between African Americans hair density and malaria. He states that “the densest hair is generally found in the same places where malaria is most common” (63). This selective advantage of having dense hair, allowed the Mediterranean populations to survive and reproduce, which over time caused an that trait to become dominant. The density of the hair makes the mosquitoes not able to land and bite on the skin as it is covered with hair; it makes getting blood more difficult for the mosquitoes so they are less likely to bite the skin and infect the body with malaria. In contrast, Africans did not evolve into a dense haired population because of the extreme heat conditions it would not be an advantage for the body in order to maintain homeostasis. Although this advantage was beneficial for malaria, it made the people with dense hair more prone to sickle-cell anemia.
ReplyDeleteDense hair is still prevalent in Mediterranean areas because there has not been a selective pressure to cause the trait to be unfavorable in that environment. This has left those populations with dense hair to continually be able to reproduce causing the passing on of the trait. There is no such thing as ‘phasing out’ of traits in populations. When a trait becomes extinct or not present in a population it is due to a factor which lead that organism with the trait to die and not reproduce, thus not passing on the trait to offspring. Over a long period of time, the population sees an extinction of the trait because of the inability for the trait to be passed down.
Another example of a disease which two separate adaptations arise based on geographical location is cholera. It is caused by ingesting contaminated food or water with the bacterium Vibrio cholerae (http://www.who.int/topics/cholera/about/en/index.html). This is dominate in South American countries due to hygiene problems and inadequate health care. Although this disease can be easily prevented, in many regions it is common and affects great parts of the population because the people do not have the advantage of clean sources of food and water. Whereas in a suburban home in America, cholera is not a concern because of the beneficial hygiene resources that is received.
Sigal Sasson (ssasson3@students.d125.org)
On page 62 of “Survival of the Sickest, Dr. Moalem described how all humans are believed to have evolved from Africa about 250,000 years ago before some began a journey northwards towards the middle east, then right to current day Asia, or left to Central Europe,and while some continued north to reach North and South America. And the environmental each group experienced created evolutionary factors/pressures which eventually led into the changes we see between populations today. He gave an example of dense hair on the legs and forearms as defense against malaria carried by female anopheles mosquitoes. The thick hair prevents the female anopheles mosquito from landing on a victim's skin to suck up his/her blood and possibly release plasmodium which results in malaria. Those that had this physical trait had protection against malaria and they managed to survive and reproduce resulting in an increase in that trait in the population. This relates to Big Idea 1: The process of evolution drives the diversity and unity of life. This physical trait is mainly found in places where malaria is dominant such as the eastern Mediterranean basin. But malaria is also dominant in Africa but this physical trait is not favorable because the heat in Africa created an evolutionary factor which made thick body hair an unfavorable trait because it would lead to overheating of the body and perhaps death. Africans are instead prone to sickle-cell anemia which protect them against malaria.
ReplyDeleteThe physical trait of dense leg and forearm hair still probably exists in the Mediterranean because unlike Africa, the weather conditions in the Mediterranean can become very cold similar to our American climate.(http://en.wikipedia.org/wiki/Mediterranean_climate) If idividuals have thick body hair in such a climate, it would help provide warmth to the individual during cold weather and this trait would also be an advantage based on their location. There have probably been no evolutionary pressures to cut down the observance of the trait within their population. Just as Sigal stated, traits can’t phase out in a population. Instead, individuals with unfavorable traits die but those with favorable traits live and pass on their traits to their offspring which eventually leads to the evolution of the population.
Another disease which has two distinct adaptations based on a geographical area would be the African Trypanosomiasis, another known as the “sleeping sickness”. This is caused by when trypanosomes enter into the bloodstream which two stages of symptoms, either the haemolymphatic phase, which is characterized by fever, headaches, joint pains, and itching, or the neurological phase which leads to the disruption of the sleep cycle. This disease is only found in Africa because only Africa contains the biological vector called the Tsetse fly which can carry trypanosomes from one organism to another. In America, and in other parts of the world, the tsetse fly cannot survive the weather conditions so trypanosomes cannot be spread between individuals in a way to cause the sleeping sickness.(http://www.infoplease.com/ipa/A0903696.html)
Prince Morkeh (pmorkeh4@students.d125.org)