Anthropology 1LW Hasten Thuy Le05/03/2018″Race” Deconstruction1.
Polymorphhic traits: + What is a polymorphic trait? What causes a trait to be polymorphic? A genetic trait is polymorphic when the locus has two alleles. Therefore, a polymorphic trait has more than one form of the traits. For example, blood type is a polymorphic trait. + Explain the kinds of phenotypes that result from polymorphic traits: Since a polymorphic trait has more than one allele, the phenotypes are also varied. For example, for the human blood types, there are three alleles which are A, B, and O to express four phenotypes which are type A, B, AB, and O. +Why are polymorphic traits relevant to the deconstruction of “race”? The reason is that the polymorphic trait causes skin color. Because of natural selection, different environment selects different kind of traits (or phenotypes).
In the warm (or hot) weather, long arms and legs have positive selection because long arms and legs mean the more surface area. Therefore, the body can sweat easily to balance the body temperature under the hot weather. Oppositely, in the cold weather, short arms and legs have positive selection because short arms and legs mean the less surface area. Therefore, the body can avoid losing heat under the cold weather. And the same process for dark and light skin color.2.
Polytypic species: +What does it mean to be polytypic? What causes a polytypic phenotype? Polytypic means that there is more than one type within the species. A polytypic phenotype is caused by the natural selection (or selection pressure) – different environment selects different type of phenotypes. +How are polytypic phenotypes relevant to the deconstruction of “race”? Since the polytypic causes more than one type of phenotypes within the species, people are placed in different categories, which base on their skin color, hair color, hair form, eye color and so on. And those categories are called “race”.3.
Continuous traits vs. Mendelian traits: +Explain the difference between a continuous trait and a Mendelian trait in terms of their resulting phenotypes: Mendelian traits are discrete or discontinuous, because their phenotypes don’t overlap. They are separated into clearly categories. Or in other words, the phenotypes of Mendelian traits are not continuous variation. For example, there are four completely different types of blood in human – type A, B, AB, and O. Continuous or polygenic traits shows the continuous variation. That means there is no category because their phenotypes overlap too much. Skin, hair, and eye color are some example of continuous traits.
Moreover, most polygenic traits can be measured on the scale such as height and weight, which the Mendelian traits cannot be measured in the same way. +What cause a trait to be continuous? What causes a trait to be Mendelian? Mendelian traits are controlled by alleles at only one gene, while continuous traits are coded by more than one gene. +Why is an understanding of continuous traits important for the deconstruction of “race”? Melanin determines the color of skin in human, which means the amount of melanin plays an important role in determining the skin color of human is either dark or light. And the produced melanin is controlled by interactions between different genes.
Therefore, the understanding of continuous traits is important for the deconstruction of “race” because it can be a good explanation for the variation of skin color in human.4.The UV radiation hypothesis: +Explain precisely why natural selection favored the development of dark skin in the first humans. First human or early hominins lived in the tropics which have more intense UV radiation than any other areas on the Earth. Moreover, they were naked and outdoor all the time, so they did not have anything to protect themselves from the sun exposure. Therefore, natural selection selects dark skin color, who have high level of melanin production to protect themselves under the harsh weather. +When and where did this adaptation occur? This occurred in Africa during the first evolution of human being.
+Explain precisely how the adaptation occurred: Since the weather was really intense in UV radiation during the first evolution of human beings, the natural selection selects positively dark skin color, which has a better adaptation to the environment because they have a high level of melanin production to protect themselves. For the light skin individuals, they have the low level of melanin production, and live under this kind of weather, infection and cancer are unavoidable. Eventually, they are dead and no longer survived on the Earth. On the other words, the dark skin color has positive selection, while the light skin color has the negative selection.5.The folate hypothesis: +Explain that folate has to do with the development of dark skin in the first human: Folate, which is a B vitamin, is an essential nutrient in human body, especially pregnant women. The insufficient level of folate can cause the developmental disorder for the baby and miscarried for the mother. Therefore, the dark skin evolved to protect folate from the damage of UV radiation.
+When and where did this adaptation occur? This occurred in Africa during the first evolution of human beings. +How the adaptation occurred? The natural selection selects positively on the dark skin color, which has a better adaptation to the environment. Dark skin color individuals have better protective response to the damage of UV radiation on folate. Therefore, the dark skin pregnant women can give birth healthily and survive. For the light skin pregnant women, the UV radiation breaks down the folate in their body, which leads to the insufficient level of folate. Eventually, they miscarry or give an unhealthy birth with the developmental disorders and then they are dead.
In other words, the light skin has a negative selection, while the dark skin has a positive selection and survive.6. The vitamin D hypothesis: +What vitamin D has to do with the adaptation of skin color? Vitamin D is an essential nutrient in human body, especially to the pregnant women. The insufficient level of vitamin D can cause rickets during the childhood, and the death of both mother and infant baby during childbirth.
Moreover, vitamin D can be consumed by the interaction between UV radiation and special cholesterol. Therefore, the environment pressed the positive pressure on the light skin individuals which have better adaptation to the environment. And the dark skin individuals have the negative selection because they have the high level of melanin to protect themselves from the UV radiation. +Where and when this adaptation occurred? This happened in Europe and Asia after 50,000 years in Africa. +Explain precisely how the adaptation occurred: When the hominins moved out of Africa to go to Europe and Asia, they had to face a different selective pressure when the weather got colder and had less UV radiation. Therefore, the environment pressed the positive pressure on the light skin individuals, while it pressed the negative pressure on the dark skin individuals.