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Evolutionary theories

It is suggested that the early hominin evolved in East Africa around 3 million years ago. The dramatic phenotypic change from primate to early hominin is hypothesized to have involved the extreme loss of body hair – except for areas most exposed to UV radiation, such as the head – to allow for more efficient thermoregulation in the early hunter-gatherers. The skin that would have been exposed upon general body hair loss in these early hominins would have most likely been non-pigmented, reflecting the pale skin underlying the hair of our chimpanzee relatives. A positive advantage would have been conferred to early hominids inhabiting the African continent that were capable of producing darker skin – those who first expressed the eumelanin-producing MC1R allele – which protected them from harmful epithelium-damaging ultraviolet rays. Over time, the advantage conferred to those with darker skin may have led to the prevalence of darker skin on the continent. The positive advantage, however, would have had to be strong enough so as to produce a significantly higher reproductive fitness in those who produced more melanin. The cause of a selective pressure strong enough to cause this shift is an area of much debate. Some hypotheses include the existence of significantly lower reproductive fitness in people with less melanin due to lethal skin cancer, lethal kidney disease due excess vitamin D formation in the skin of people with less melanin, or simply natural selection due to mate preference and sexual selection.

When comparing the prevalence of albinism in Africa to its prevalence in other parts of the world, such as Europe and the United States, the potential evolutionary effects of skin cancer as a selective force due to its effect on these populations may not be insignificant. The prevalence of albinism in some ethnic groups in sub-Saharan Africa is around 1 in 5,000, while in Europe and the US it is 1 in 20,000 [31]. It would follow, then, that there would be stronger selective forces acting on albino populations in Africa than on albino populations in Europe and the US. Rates as high as 1 in 1,000 have been reported for some populations in Zimbabwe and other parts of Southern Africa [32]. In two separate studies in Nigeria, people suffering from albinism were found to be of reproductively significant age more often than not. One study found that 89% of people diagnosed with albinism are between 0 and 30 years of age, while the other found that 77% of albinos were under the age of 20 [33]. --Quinones-betancourt.2 (talk) 05:18, 17 November 2014 (UTC)

link to article: https://en.wikipedia.org/wiki/Albinism

FINAL DRAFT STARTS HERE

Oculocutaneous (OCA) albinism is a recessive autosomal condition characterized by reduced melanin production in the eyes, skin and hair (Genetics Home Reference). One study estimated that approximately 1 in 17,000 people suffer from albinism, meaning that 1 in 70 people are carriers of the allele coding for OCA (Gronskov 2007). OCA is classified into four different groups – OCA1, OCA2, OCA3, and OCA4. The four types of OCA are categorized by the action of their genetic defects, which result in differential melanin activity in the eyes, skin and hair. OCA1 is caused by defective tyrosinase enzymes, which would normally convert tyrosine amino acids into pigment. OCA1 is further divided into OCA1A, in which the enzyme is totally inactive, and OCA1B, in which the enzymes function only slightly. OCA2, OCA3, and OCA4 are all caused by defective proteins that are necessary for the tyrosinase enzyme to function properly. The defective protein in OCA2 is P protein, the protein in OCA3 is TYRP1, and the protein in OCA4 is SLC45A2. OCA3 individuals are capable of producing more pigment that OCA2 and OCA4 individuals. OCA1A is the most severe form of albinism, while the rest are more mild manifestations. While the incidence of skin cancer may vary among the different forms, the likelihood of an albino person developing skin cancer compared to a non-albino person is increased for each form of the condition (Gronskov 2007). The detrimental effects of skin cancer on albino populations in early the early homonin populations inhabiting the African continent has recently been examined as a possible explanation for the evolution of dark skin (NOAH). It is suggested that the early hominin evolved in East Africa around 3 million years ago (Greaves 2014). The dramatic phenotypic change from primate to early hominin is hypothesized to have involved the extreme loss of body hair – except for areas most exposed to UV radiation, such as the head – to allow for more efficient thermoregulation in the early hunter-gatherers. The skin that would have been exposed upon general body hair loss in these early hominins would have most likely been non-pigmented, reflecting the pale skin underlying the hair of our chimpanzee relatives. A positive advantage would have been conferred to early hominids inhabiting the African continent that were capable of producing darker skin – those who first expressed the eumelanin-producing MC1R allele – which protected them from harmful epithelium-damaging ultraviolet rays. Over time, the advantage conferred to those with darker skin may have led to the prevalence of darker skin on the continent. The positive advantage, however, would have had to be strong enough so as to produce a significantly higher reproductive fitness in those who produced more melanin. The cause of a selective pressure strong enough to cause this shift is an area of much debate. Some hypotheses include the existence of significantly lower reproductive fitness in people with less melanin due to lethal skin cancer, lethal kidney disease due excess vitamin D formation in the skin of people with less melanin, or simply natural selection due to mate preference and sexual selection (Greaves 2014). Scientists, including Charles Darwin, have long dismissed the idea that skin cancer could have acted as a force of evolutionary biology. The dismissal of this idea is based on an evolutionary principle that deems the time beyond the reproductive years as evolutionarily insignificant (Greaves 2014). This time is not evolutionarily significant because individuals that were at one point capable of reproducing have most likely already done so. These individuals’ abilities to survive beyond this point, therefore, have no effect on the gene pool of the next generation. Jared Diamond, in his 1991 publication, The rise and fall of the third chimpanzee, acknowledges the advantage of darker skin in areas with high levels of sun exposure, but says that, “…skin cancer and sunburn cause little debilitation and few deaths. As agents of natural selection, they have an utterly trivial impact compared to infectious diseases of childhood” (Diamond 1991). The fact that the onset of epithelial carcinomas often occurs later in life, beyond the reproductive years, and that they are rarely lethal, heads the argument that claims that skin cancer alone could not have been the cause of evolutionary change across generations. Instead, Diamond proposes a competing theory which states that ultraviolet radiation in less pigmented people produces excesses vitamin D because of a lack of melanin-induced protection and can cause kidney disease, effectively lowering the reproductive fitness of those with lighter skin that are susceptible to this damage (Diamond 1991). Darwin, on the other hand, who dismissed the idea that skin damage and epithelial cancer due to sun exposure would have cause a significant selective force, argued that mate preference and sexual selection was the most probable cause of the shift from dark skin to light skin, an alternate theory that Diamond also proposes in his 1991 publication (Greaves 2014). The dismissal of skin cancer as a significant selective force, however, considers only the effects of skin cancer on non-albino populations and fails to take into account the effects of ultraviolet radiation on albino populations. When comparing the prevalence of albinism in Africa to its prevalence in other parts of the world, such as Europe and the United States, the potential evolutionary effects of skin cancer as a selective force due to its effect on these populations may not be insignificant. The prevalence of albinism in some ethnic groups in sub-Saharan Africa is around 1 in 5,000, while in Europe and the US it is 1 in 20,000 (Greaves 2014). It would follow, then, that there would be stronger selective forces acting on albino populations in Africa than on albino populations in Europe and the US. Rates as high as 1 in 1,000 have been reported for some populations in Zimbabwe and other parts of Southern Africa (Hong et al 2006). Those diagnosed with albinism are at a higher risk for developing skin cancer and other disorders of body’s the external organs. Their increased susceptibility puts them at a higher risk for mortality at a younger age, before the end of their reproductive years. It is important to keep in mind that skin cancer among albinos, analogous to its action in non-albinos, will not decrease Darwinian fitness if it results in death only after reproduction (Woolfe 2005). In two separate studies in Nigeria, however, people suffering from albinism were found to be of reproductively significant age more often than not. One study found that 89% of people diagnosed with albinism are between 0 and 30 years of age, while the other found that 77% of albinos were under the age of 20 (Hong et al 2006). These findings suggest that skin cancer may have played a significant role as a selective force that increased the comparative fitness, and therefore the prevalence, of people with darker skin. Some theories propose that, over time, the number of people with albinism in places with more potent sun exposure may have dwindled and genes coding for melanin production would have proliferated. It makes sense that, in places where albinism is relatively more common, effects on people and populations suffering from albinism would have the greatest impact. With more people suffering from a condition that affords them a predisposition to other lethal diseases such as skin cancer, a stronger selection toward proliferation of more fit, darker-skinned people and populations may occur over time. Nonetheless, this is a relatively new hypotheses and it is extremely difficult to come to a consensus when examining evolutionary phenomena that occurred millions of years ago. When dealing specifically with albinism, however, one must always wonder why such detrimental alleles remain in the population, especially in areas of the world where their negative effects are compounded—predisposition to skin cancer as well as kidney disease and also lowered fitness due social selection (Yokoyama 1983). The most widely accepted explanation is that albinism around the world is still highly stigmatized. In some parts of Africa, albinos are hunted for witchcraft purposes. Populations with a prevalence of albinism are usually isolated from the rest of the population. Their reproductive fitness is effectively lowered outside of their own communities and they are forced to inbreed, resulting in a proliferation of detrimental homologous recessive allele pairs (Cruz-Inigo 2011).

Literature Cited

Cruz-Inigo AE, Ladizinski B, Sethi A. 2011. Albinism in Africa:Stigma, Slaughter and Awareness Campaigns. Dermatologic Clinics [Internet]. [cited 2014 Oct 26] 29(1):79-87. Available from: http://www.sciencedirect.com/science/article/pii/S0733863510001403

Diamond J. 1991. The rise and fall of the third chimpanzee. Random Century [Internet]. [cited 2014 Oct 24]. Available from: http://www.beaconschool.org/~bfaithfu/thirdchimpanzee.pdf

Greaves M. 2014. Was skin cancer a selective force for black pigmentation in early hominin evolution?. Royal Society Publishing [Internet]. [cited 2014 Oct 18]. Available from: http://royalsocietypublishing.org/content/281/1781/20132955

Gronskov K, Ek J, Brondum-Nielsen K. 2007. Oculocutaneous albinism. Orphanet Journal of Rare Diseases [Internet]. [cited 2014 Oct 19] 2:43. Available from: http://www.biomedcentral.com/content/pdf/1750-1172-2-43.pdf

Oculocutaneous albinism. 2007 Mar. Genetics Home Reference (GHR); [2014 Nov 11, cited 2014 Nov 14]. Available from: http://ghr.nlm.nih.gov/condition/oculocutaneous-albinism

Hong ES, Zeeb H, Repacholi MH. 2006. Albinism in Africa as a public health issue. BioMed Central [Internet]. [cited 2014 Oct 17] 6:212. Available from: http://www.biomedcentral.com/1471-2458/6/212/

What is Albinism? [Internet]. East Hampstead (NH): The National Organization for Albinism and Hypopigmentation (NOAH); [cited 2014 Oct 24]. Available from: http://www.albinism.org/publications/what_is_albinism.html

Woolfe CM. 2005. Albinism (OCA2) in Amerindians. American Journal of Physical Anthropology [Internet]. [cited 2014 Dec 18] 128(41):118–140. Available from: http://onlinelibrary.wiley.com/doi/10.1002/ajpa.20357/abstract

Yokoyama S. 1983. Social Selection and Evolution of Human Diseases. WorldCat [Internet]. [cited 2014 Oct 19] 62:61-66. Available from: http://osu.worldcat.org/title/social-selection-and-evolution-of-human-diseases/oclc/5152145349&referer=brief_results

Albinism and Skin Pigmentation - first draft

Oculocutaneous (OCA) albinism is a recessive autosomal condition characterized by reduced melanin production in the eyes, skin and hair. One study estimated that approximately 1 in 17,000 people suffer from albinism, meaning that 1 in 70 people are carriers of the allele coding for OCA (Gronskov 2007). OCA is classified into four different groups – OCA1, OCA2, OCA3, and OCA4. The four types of OCA are categorized by the action of their genetic defects, which result in differential melanin activity in the eyes, skin and hair. OCA1 is caused by defective tyrosinase enzymes, which would normally convert tyrosine amino acids into pigment. OCA1 is further divided into OCA1A, in which the enzyme is totally inactive, and OCA1B, in which the enzymes function only slightly. OCA2, OCA3, and OCA4 are all cause by defective proteins that are necessary for the tyrosinase enzyme to function properly. The defective protein in OCA2 is P protein, the protein in OCA3 is TYRP1, and the protein in OCA4 is SLC45A2. OCA3 individuals are capable of producing more pigment that OCA2 and OCA4 individuals. OCA1A is the most severe form of albinism, while the rest are milder. While the incidence of skin cancer may vary among the different forms, the likelihood of an albino person developing skin cancer compared to a non-albino person is increased for each form of the condition (Gronskov 2007). The detrimental effects of skin cancer on albino populations in early the early homonin populations inhabiting the African continent has recently been explored as a possible explanation for the evolution of dark skin (NOAH). It is suggested that the early hominin evolved in East Africa around 3 million years ago. The dramatic phenotypic change from primate to early hominin is hypothesized to have involved the extreme loss of body hair – except for areas most exposed to UV radiation, such as the head – to allow for more efficient thermoregulation in the early hunter-gatherers. The skin that would have been exposed upon general body hair loss in these early hominins would have most likely been non-pigmented, reflecting the pale skin underlying the hair of our chimpanzee relatives. A positive advantage would have been conferred to early hominids inhabiting the African continent that were capable of producing darker skin – those who first expressed the eumelanin-producing MC1R allele – which protected them from harmful epithelium-damaging ultraviolet rays. Over time, the advantage conferred to those with darker skin may have led to the prevalence of darker skin on the continent. The positive advantage, however, would have had to be strong enough so as to produce a significantly higher reproductive fitness in those who produced more melanin. The cause of a selective pressure strong enough to cause this shift is an area of much debate. Some hypotheses include the existence of significantly lower reproductive fitness in people with less melanin due to lethal skin cancer, lethal kidney disease due excess vitamin D formation in in the skin of people with less melanin, or simply natural selection due to mate preference and sexual selection (Greaves 2014). Scientists, including Charles Darwin, have long dismissed the idea that skin cancer could have acted as a force of evolutionary biology. The dismissal of this idea is based on an evolutionary principle that deems the time beyond the reproductive years as evolutionarily insignificant (Greaves 2014). This time is not evolutionarily significant because individuals that were at one point capable of reproducing have most likely already done so, and their ability to survive beyond this point, therefore, has no effect on the gene pool of the next generation. Jared Diamond, in his 1991 publication, The rise and fall of the third chimpanzee, acknowledges the advantage of darker skin in areas with high levels of sun exposure, but says that, “…skin cancer and sunburn cause little debilitation and few deaths. As agents of natural selection, they have an utterly trivial impact compared to infectious diseases of childhood” (Diamond 1991). The fact that the onset of epithelial carcinomas often occurs later in life, beyond the reproductive years, and that they are rarely lethal, heads the argument that claims that skin cancer alone could not have been the cause of evolutionary change across generations. Instead, Diamond proposes a competing theory which states that ultraviolet radiation in less pigmented people produces excesses vitamin D because of a lack of melanin-induced protection and can cause kidney disease, effectively lowering the reproductive fitness of those with lighter skin that are susceptible to this damage (Diamond 1991). Darwin, on the other hand, who dismissed the idea that skin damage and epithelial cancer due to sun exposure would have cause a significant selective force, argued that mate preference and sexual selection was the most probable cause of the shift from dark skin to light skin, an alternate theory that Diamond also proposes in his 1991 publication (Greaves 2014). The dismissal of skin cancer as a significant selective force, however, considers only the effects of skin cancer on non-albino populations and fails to take into account the effects of ultraviolet radiation on albino populations. When comparing the prevalence of albinism in Africa to its prevalence in other parts of the world, such as Europe and the United States, the potential evolutionary effects of skin cancer as a selective force due to its effect on these populations may not be insignificant. The prevalence of albinism in some ethnic groups in sub-Saharan Africa is around 1 in 5,000, while in Europe and the US it is 1 in 20,000 (Greaves 2014). Rates as high as 1 in 1,000 have been reported for some populations in Zimbabwe and other parts of Southern Africa (Hong et al 2006). Those diagnosed with albinism are at a higher risk for developing skin cancer and other disorders of body’s the external organs. Their increased susceptibility puts them at a higher risk for mortality at a younger age, before the end of their reproductive years. It is important to keep in mind that skin cancer among albinos, analogous to its action in non-albinos, will not decrease Darwinian fitness if it results in death only after reproduction (Woolfe 2005). However, in two separate studies in Nigeria, one study found that 89% of people diagnosed with albinism 0 and 30 years of age, while the other found that 77% of albinos were under the age of 20 (Hong et al 2006). These findings suggest that skin cancer may have played a significant role as a selective force that increased the comparative fitness, and therefore the prevalence, of people with darker skin. Some theories propose that, over time, the number of people with albinism in places with more potent sun exposure would have dwindled and genes coding for melanin production would have proliferated. It makes sense that, in places where albinism is relatively more common, effects on people and populations suffering from albinism would have the greatest impact. With more people suffering from a condition that affords them a predisposition to other lethal diseases such as skin cancer, a stronger selection toward proliferation of more fit, darker-skinned people and populations may occur over time. Nonetheless, this is a relatively new hypotheses and it is extremely difficult to come to a consensus when examining evolutionary phenomena that occurred millions of years ago. When dealing specifically with albinism, however, one must always wonder why such detrimental alleles remain in the population, especially in areas of the world where their negative effects are compounded. The most widely accepted explanation is that albinism around the world is still highly stigmatized. In some parts of Africa, albinos are hunted for witchcraft purposes. Populations with a prevalence of albinism are usually isolated from the rest of the population. Their reproductive fitness is effectively lowered outside of their own communities and they are forced to inbreed, resulting a proliferation of detrimental homologous recessive allele pairs (Cruz-Inigo 2011).

Literature Cited

Cruz-Inigo AE, Ladizinski B, Sethi A. 2011. Albinism in Africa:Stigma, Slaughter and Awareness Campaigns. Dermatologic Clinics [Internet]. [cited 2014 Oct 26] 29(1):79-87. Available from: http://www.sciencedirect.com/science/article/pii/S0733863510001403

Diamond J. 1991. The rise and fall of the third chimpanzee. Random Century [Internet]. [cited 2014 Oct 24]. Available from: http://www.beaconschool.org/~bfaithfu/thirdchimpanzee.pdf

Greaves M. 2014. Was skin cancer a selective force for black pigmentation in early hominin evolution?. Royal Society Publishing [Internet]. [cited 2014 Oct 18]. Available from: http://royalsocietypublishing.org/content/281/1781/20132955

Gronskov K, Ek J, Brondum-Nielsen K. 2007. Oculocutaneous albinism. Orphanet Journal of Rare Diseases [Internet]. [cited 2014 Oct 19] 2:43. Available from: http://www.biomedcentral.com/content/pdf/1750-1172-2-43.pdf

Hong ES, Zeeb H, Repacholi MH. 2006. Albinism in Africa as a public health issue. BioMed Central [Internet]. [cited 2014 Oct 17] 6:212. Available from: http://www.biomedcentral.com/1471-2458/6/212/

What is Albinism? [Internet]. East Hampstead (NH): The National Organization for Albinism and Hypopigmentation (NOAH); [cited 2014 Oct 24]. Available from: http://www.albinism.org/publications/what_is_albinism.html

Woolfe CM. 2005. Albinism (OCA2) in Amerindians. American Journal of Physical Anthropology [Internet]. [cited 2014 Dec 18] 128(41):118–140. Available from: http://onlinelibrary.wiley.com/doi/10.1002/ajpa.20357/abstract

Yokoyama S. 1983. Social Selection and Evolution of Human Diseases. WorldCat [Internet]. [cited 2014 Oct 19] 62:61-66. Available from: http://osu.worldcat.org/title/social-selection-and-evolution-of-human-diseases/oclc/5152145349&referer=brief_results

Chosen Topic

Due to the general lack of information on albinism on Wikipedia, I have decided on oculocutaneous albinism as my topic – the group of conditions that affect the pigmentation of skin, hair, and eyes.

Annotated Bibliography

1. Boissy, Raymond E., et al. “Mutation in and Lack of Expression of Tyrosinase-Related Protein-1 (TRP-1) in Melanocytes from an Individual with Brown Oculotaneous Albinism: A New Subtype of Albinism Classified as ‘OCA3’.” The American Journal of Human Genetics Jun. 1996: 1145-56. Web. 10 Sep. 2014. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1915069/?page=1.

Discusses the common forms of human oculocutaneous albinism (OCA) and their genetic cause. Introduces other types of OCA that have been identified, but not located on loci. The paper discusses gene mutations that may be the cause of one of the other types of OCA in humans.

2. Genetics Home Reference. U.S. National Library of Medicine. 8 Sep. 2014. Web. 10 Sep. 2014. http://ghr.nlm.nih.gov/condition/oculocutaneous-albinism.

This reviewed entry defines oculocutaneous albinism (OCA), describing its general clinical manifestations and the characteristics of each type. It goes on to identify OCA-related genes and explains the conditions inheritance pattern.

3. Gronskov, Karen, et al. “Oculocutaneous albinism.” Orphanet Journal of Rare Diseases 2 Nov. 2007: 2:43, 1-8. Web. 10 Sep. 2014. http://www.biomedcentral.com/content/pdf/1750-1172-2-43.pdf.

This article identifies the five types of oculocutaneous albinism (OCA) and their clinical manifestations. It goes on to address the genes responsible for the different types of the disease. It was interesting to me that this article referred to OCA as a disease, where I have mostly seen albinism referred to as a condition.

4. Hermansky, F., and Pudlak, P. “Albinism Associated with Hemorrhagic Diathesis and Unisual Pigmented Reticular Cells in the Bone Marrow: Report of Two Cases with Histochemical Studies.” Blood 1 Feb. 1959: 162-69. Web. 10 Sep. 2014. http://www.bloodjournal.org/content/14/2/162.full-text.pdf+html.

This paper analyzes the results of a hemorrhagic disorder study of two unrelated patients with albinism. Each patient study and analysis was done independently. The researchers suggest that the similarities in the results of the study – pseudohemophilia and unusual bone marrow cells – indicate a new congenital anomaly associated with albinism.

5. Newton, J.M., et al. “Mutations in the Human Orthologue of the Mouse underwhite Gene (uw) Underlie a New Form of Oculocutaneous Albinism, OCA4” Science Direct Nov. 2001: 981-88. Web. 10 Sep. 2014. http://www.sciencedirect.com/science/article/pii/S0002929707613147.

This paper discusses the prevalence of oculocutaneous albinism, the effects of reduced pigmentation during eye development, and genes and mutations associated with oculocutaneous albinism.

Three Suggestions and One Sentence Addition

https://en.wikipedia.org/wiki/Albinism

Addition: A mutation in the human TRP-1 gene may result in the deregulation of melanocyte tyrosinase enzymes, a change that is hypothesized to promote brown versus black melanin synthesis, resulting in a third oculocutaneous albinism (OCA) genotype, ″OCA3.″

Three Suggestions: 1)	Expand on the rare OCA forms inherited from one parent (genetics section). What are these rare forms? Does single-parent inheritance mean the parents are homozygous for the trait as well? How do these forms compare to the other OCA forms? 2)	Statistics on albinism prevalence throughout the world would be a great addition to this page! 3)	The hyperlink for OCA2 (genetics section) leads to a page with quite a bit of information on the OCA2 gene. The same cannot be said for the OCA1 link. Does anyone have any information on OCA1? This would benefit the main albinism page.

Quinones-betancourt.2 (talk) 02:26, 1 October 2014 (UTC)