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Sickle cell anemia and skin pigmentation as examples of human evolution
Natural selection only happens on the population heritable characteristics in a selective manner. Selection for beneficial alleles results to an increase of their frequency in the population and selecting against destructive alleles thus decreasing their frequency in the population. However, natural selection does not act on individual alleles but an entire organism. As natural selection influence allele’s frequencies in a population, individuals can become more or less genetically similar and phenotypically the organism can either be similar or more disparate. Natural selection for superior genes is a justification for the numerous adaptive characteristics that suits an organism to its environment. In people, genetic mutations are considered neutral presenting neither positive nor negative traits to the carrier. The variant DNA occurs by likelihood and once selection occurs the sole purpose is to purify or destroy harmful mutation rather than supporting multiplication of superior traits.
Sickle cell anemia as an example of human evolution
Sickle cell mutation results in the creation of abnormal hemoglobin. Every individual has two copies of hemoglobin genes which create normal hemoglobin when an offspring inherits two mutant duplicate hemoglobin genes an abnormal type of hemoglobin protein will cause the red blood cells to lose oxygen, wrap in the form of a sickle shape in times of high exercise (Livingstone 546). Such sickles cells will get stuck in the blood vessels causing pain, fever, swelling and resultant tissue destruction that causes death. Moreover, people with sickle cells do not suffer almost as severely from the illness. The sickle cell genes are more prevalent within regions of Africa had hit with malaria.
Evolutionary links between malaria resistance and sickle cell traits show that humans can undergo evolution and adapt. In 1940 Haldane observed that many red blood cells disorder were prominent in tropical areas where malaria was endemic, an illness that kills 1.5 million people yearly (Livingstone 555). According to Haldane hypothesis, these disorders were common in these regions due to natural selection that was meant to increase the prevalence of traits that protect individuals from malaria. Further research demonstrated that the geographical distribution of the sickle cell mutation in the beta hemoglobin gene was limited to Africa and correlated to malaria endemically. This proved that natural selection increased the genetic resistance to malaria. It becomes that in these African regions carriers of HbS were naturally selected owing to the beneficial traits which conferred immune towards malaria. The red blood cells of such people containing a few abnormal hemoglobin had a propensity to be sickled celled once infected by malaria bacteria.
In regions with widespread sickle cell genes, the beneficial resistance towards malaria is selective. The worst-case scenario is brought forth by the increased chances of getting born with sickle cell anemia. In the ent that both parents have sickle cell traits the chances of the offsprings getting sickle cells and being resistent to malaria is 50%.It is worth noting that various HBB alleles are not the only ones offering immunity against malaria. Geographical distribution also correlates to malaria endemicity. A striking geographical difference exists for the mutation in the Duffy antigen which disrupts the proteins through mutation thus conferring protection against P vivax malaria and occurs throughout sub-Saharan Africa yet it is absent outside Africa (Livingstone 557).
Skin pigmentation as a form of evolution
Environmental factors can put selective pressure on people. For instance, as the Europeans and Asians moved into Africa continent, they faced environmental changes characterized the varying amount of sunlight and temperatures. Some areas were humid while others very cold (Jablonski 46). At the genetic level and gene composition, people have faced positive selection to adequately produce skin pigment that best suits them in addition to the quantity of sunlight they receive.
. It is worth noting that skin pigmentation is adaptive and is related to the regulation of ultraviolet radiation. In the earlier stages of evolution, human ancestors had dark skin, hair, and eyes. Since this initial stages, genetic changes have resulted to changes in this features, changes in genes such as TYRP1 for instances makes Solomon islanders blond while the HERC2 mutation that results in blue eyes changes to MC1R that causes red hair to sprout instead of black ones.
It is factual to point out that human skin color evolves as an adaptation to the local environment. High UVR has led to dark skin color while low UVR leads to light skinned color. By natural selection, genes respond to environmental conditions for humans to survive in their environment(Jablonski 48). Take an example of melanin production that came as a response to UVR to protect against consequences of ultraviolet rays in low altitude areas while depigmentation occurred as people moved from low altitude areas to high altitude areas leading to lightly skinned individuals.
Forces of evolution
The main forces of evolution are genetic drift, mutation, genetic flow and natural selection (Stephens and Christopher 550). In natural selection, the best-adapted offspring will produce the most offspring’s that will carry forth their ancestral genes that gave their parents an upper hand. Genetic drift, on the other hand, deals with chances of survival of alleles while gene flows occur when genes are transported from one area to another. On the other and, genetic mutation entails random changes in an organism deoxyribonucleic acid that impacts all aspects of the organism life. With this in mind, the conventional forces of evolution that lay a role in sickle cell anemia and skin pigmentation in humans are natural selection and genetic mutations (Stephens and Christopher 555).
To begin with, genetic mutation interferes with the gene that is responsible for the normal formation of hemoglobin proteins. Such genes drift, and the likelihood of occurring the next offspring’s are high. On the other hand, skin pigmentation is a product of natural selection; the only organism that could better suit and adapt in the prevailing environmental condition had a chance of survival. Research has proved that human variants in the DNA justify the difference in pigmentation amongst West Africans and the Europeans and the Europeans variant was a target of section (Stephens and Christopher 560). Inside related works by Angela alongside her equal, studied numerous genes include the metabolism ones and discovered that the alleles of such genes demonstrated proof of positive selection as well as correlates positively with climate (Livingstone 540).
Works cited
Jablonski, Nina G. “Human skin pigmentation as an example of adaptive evolution.” Proceedings of the American Philosophical Society 156.1 (2012): 45-57.
Livingstone, Frank B. “Anthropological Implications of Sickle Cell Gene Distribution in West Africa1.” American Anthropologist 60.3 (1958): 533-562.
Stephens, Christopher. “Selection, drift, and the “forces” of evolution.” Philosophy of Science 71.4 (2004): 550-570.