Viviana Herrera Assignment 3 What makes a person black or white There is a substance that our body produces naturally called Melanin This substance is the responsible of our skin pigmentation The principal function of Melanin is to act as a heat absorber The quantity of melanin produced by our body depends on our geographic location First humans on earth appear in Africa and they developed a darker skin to protect themselves from their environment It is well known that people who lives in zones were the sun has less impact poles tend to have a lighter skin than people who lives in areas were the sun falls more directly If the radiation is higher the person will develop a higher quantity of melanin in his body and as a result would have a darker pigmentation However this only answer the reason why some people have different skin color It does not answer the question of why do we need to produce melanin The article Re appraisal of current theories for the development and loss of epidermal pigmentation in hominids and modern humans by Elias and Williams tries to explain why there was a loss in epidermal pigmentation producing different races of people The authors mention previous theories that tried to explain this phenomena One of the most known is the one that argues that the production of melanin is related with the production of vitamin D and that it evolves to prevent vitamin D intoxication Other theories argue that the reason of the evolution of melanin is to prevent skin cancer folic acid deficiency or to protect the person form the UV radiation Nevertheless the authors discard all those theories because there are not enough evidence to support it Viviana Herrera Instead the reason why melanin evolved in our body is related with protection Dark skins are stronger than light skins They are more resistant to infections This is because darker skins tend to be drier Microbes can only colonize humid places and if the skin is dry bacteria will not attach to the person The environment is crucial and in dry places like Africa it is required to have a permeable skin to avoid dehydration We know that homeostasis is the process of natural temperature regulation of our bodies When it is too hot we sweat in order to release the heat and get fresh However if your skin lets the sweet go away you can suffer from dehydration In such a dry and hot environment when people has to hunt and move it was necessary to develop a skin who can maintain the body fresh by sweeting but not sweeting too much in order to avoid dehydration When people started to move to different environments where this kind of skin was not necessary to survive anymore natural selection favorite the lighter skins In addition they explained pigment dilution as a result of positive selection for lighter pigmentation Elias Williams They also argue that Vitamin B is not the cause of pigment dilution given the fact that people can consume vitamin D by eating certain foods and that even a short exposition to the UV radiation can create enough vitamin D storage for a year non depending on your skin color They also discuss the fact that there is a protein that is in charge of enhance vitamin D production Finally the end up with the conclusion that the production of lighter skins is product of mutations based on the diet of the people