Introduction to Physical Anthropology
Quiz 15 :
Modern Human Biology: Patterns of Adaptation
During the evolutionary course, the primitive humans migrated through various routes to different places or areas. The nature favored light pigmented skin for those who moved to areas far away from equator whereas dark skin pigmentation was selected by the nature for the individuals dwelling in areas near to the equator. The less pigmented skin became advantageous because the decrease in sunlight means insufficient UV (Ultraviolet) radiation exposure for the adequate production of vitamin D, which is essential for proper mineralization of bones. On the other hand, dark pigmented skin became advantageous in equatorial areas because more the melanin synthesized by the Melanocytes in skin on overexposure to UV light, less will be the chances of genetic mutation leading to deadlier diseases like skin cancers and other diseases. It is not suitable to classify the humans on the basis of their skin color as the Homo sapiens or 'modern humans' have evolved from a common ancestor and evidences reveal that first ancestor evolved in Africa. The primitive human ancestor lived in Africa located near the equatorial region and thus, had a deeply pigmented skin due to large amount of melanin synthesis by the melanocytes so as to protect the individual from the potentially harmful ultraviolet (UV) radiations.
The pigmentation of skin in humans is influenced by three substances including hemoglobin, carotene proteins and mainly the pigment called melanin. Melanocytes present in the outer layer of skin secreted the granular substance termed as melanin. Melanin plays a very crucial role as it absorbs the potentially dangerous ultraviolet (UV) rays. The UV (ultraviolet) rays may cause genetic mutations in skin cells leading to skin cancer and can affect other organs eventually. The less pigmented skin is advantageous in northern latitudes because a decrease in sunlight meant insufficient UV radiation exposure for the adequate production of vitamin D, which is essential for proper mineralization of bones. In contrast, the people in areas near to equator such as Africa, where the rays of sun are direct and UV light exposure is most intense as well as constant, have dark or deeply pigmented skin as favored by the natural selection. It was believed that about 100 genes are involved in skin pigmentation in vertebrate. MCIR is one of these genes that affect the coloration of skin in all mammals and its human version has about 30 alleles which are associated with red hair, fair skin and a tendency to freckle. The research on DNA (Deoxyribonucleic acid) of Neanderthal revealed that some of these primitive humans had red hair and light pigmented skin due to the presence of an MCIR allele, which reduces the melanin in skin as well as hair and isn't found in modern humans.
A zoonotic disease is a disease that is transmitted through the contact with animals other than humans. The virus commonly known as HIV (Human immunodeficiency virus) is responsible for AIDS (Acquired immunodeficiency syndrome). HIV-1 is mainly that type of HIV that causes AIDS in humans. The researchers have found similarities between the DNA (Deoxyribonucleic acid) of HIV virus and the virus that is found in chimpanzees and several species of African monkey named SIV (Simian immunodeficiency virus). In its traditional hosts including chimpanzees and African monkeys, the virus called SIV do not produce any symptom and causes immune suppression that are similar to AIDS. The comparison of DNA sequences have also shown that HIV-1 evolved from a form of SIV in the host chimpanzee native to western central Africa. Since the chimpanzees in West Africa were hunted routinely for the purpose of food, thus the chimpanzee virus SIV got transmitted to humans and on several human exposures. This virus got modified to HIV at some point over the period of time. So, the HIV/AIDS is considered as a zoonotic disease. In 1959, a frozen HIV-positive blood sample taken from a West African patient was the oldest evidence of human infection.