Human origin is one of the most debated topics in anthropology. Currently there are two major propositions for the origin of anatomically modern Humans: the multiregional hypothesis and the “out of Africa”/ replacement hypothesis. Yet, these theories fail to explain the variations in skin color among human populations. What is the explanation Sean Carroll provides in chapter 7? Does Dr. Carroll’s theory on skin color weakens or strenghtens both hypotheses’ claim that our hominid ancestors originated from a small population in Africa? How So? Do you think that skin color simply reflects relatedness among humans or that people of different origins can develop the same skin tone once they migrate to a certain area due to selection pressure?
Carroll begins his theory of different skin tones by stating what skin color depends on. He said that the main determinant of skin color is the amount of melanin that is produced in the melanocytes. Melanin formation is dependent on the MC1 receptor. This receptor is what the MSH (which is the hormone that controls production of melanin) binds to, stimulating production. Another factor that aids in the making of melanin in UV radiation. Melanin acts as a “natural sunscreen” (172), absorbing different wavelengths of sunlight.
ReplyDeleteIn our world, the amount of UV radiation depends on which region you live in. Studies have shown that there are many variations of the MC1R gene (which controls how much melanin is being produced) within different groups of people. For example, in European and Asian populations, there are about 13 variations of the MC1R gene while in African populations, there are only 5 variations. According to Carroll, this is due to natural selection; while there are mutations within the African population, natural selection has only “allowed” a select few to actually survive due to the high amount of sunlight and UV rays in Africa. I think Carroll’s theory weakens the theories that our ancestors originated from Africa because Africans have the least variation in their MC1R gene pool.
I don’t think that skin tone can be changed if a person decides to move to a region with more or less sunlight due to selection pressure. If a light person goes to a place with a lot to sunlight, UV rays may stimulate production of melanin, giving them a tan. But if a dark person goes to a place with little to no sunlight, they are not going to become light. The UV rays may change the skin tone for awhile, but the person’s genes are not going to change due to a change in location.