Monday, February 20, 2012

Evolutionary Basis of Albinism

I found the first half of Dr. Sharon Moalem’s Survival of the Sickest to be fascinating. His idea that today’s detrimental and sometimes deadly health conditions, diseases, and illnesses exist because they were once beneficial and advantageous to survival is quite fascinating,

I found Dr.Moalem’s discussion of sun exposure, cholesterol, Vitamin D, and skin color to be particularly interesting. He writes that, “the wide range of human skin color is related to the amount of sun a population has been exposed to over a long period” (p.53). He further writes that, “The milk white skin of an albino is caused by an enzyme deficiency that results in the production of little or no melanin.” (p. 53) The latter line was personally significant to me as I have albinism.

Albinism is an autosomal recessive genetic condition that causes a lack of pigmentation in the hair, skin, and eyes. This results in pale hair and skin and a significant visual impairment (typically legal blindness, nystagmus, strabismus, astigmatism, photophobia, near sightedness, etc.). Because individuals with albinism do not tan and only burn upon exposure to the sun, we tend to avoid the sun (stay indoors) or slather on sunscreen even on overcast days. This results in limited UVB exposure, and our cholesterol does not get converted to Vitamin D efficiently. As a result, many of us have a Vitamin D deficiency or insufficiency.

I was disappointed that Dr. Moalem did not indirectly hypothesize or directly address how/why albinism and/or the enzyme deficiency which causes albinism may exist now due to having been particularly advantageous to survival at some point and time in the past (other than saying that human skin color is related to long-term sun exposure… I suppose this means that albinism evolved in individuals who lived in an area with no sun exposure and thus did not need any melanin…?). Currently, as global warming progresses, having albinism does not seem particularly advantageous.

I decided to do some research into this topic. While I was unable to find any credible information about the advantageous evolution of albinism in humans, it seems that albinism evolved independently in two different species of Mexican cavefish as a result of their habitats. Since these species live in perpetual darkness, over time, they have lost their pigment, and their visual acuity has also decreased.

I am curious to know whether being a carrier of the gene for albinism or having the condition itself is or was ever advantageous in some respect in humans or other species.

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