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Discover your Perfect No7 Regime. The earliest primate ancestors of modern humans most likely had light skin, like our closest modern relative—the chimpanzee.

The solution was sweating and loss of body hair. Sweating dissipated heat through evaporation. Early humans, like chimpanzees now, had few sweat glands, and most of them were located in the palms of the hand and the soles of the feet.

At times, individuals with more sweat glands were born. These humans could search for food and hunt for longer periods before being forced back to the shades.

The more they could forage, the more and healthier offspring they could produce, and the higher the chance they had to pass on their genes for abundant sweat glands.

With less hair, sweat could evaporate more easily and cool the bodies of humans faster. A few million years of evolution later, early humans had sparse body hair and more than 2 million sweat glands in their body.

Hairless skin, however, is particularly vulnerable to be damaged by ultraviolet light and this proved to be a problem for humans living in areas of intense UV radiation, and the evolutionary result was the development of dark-coloured skin as a protection.

Scientists have long assumed that humans evolved melanin in order to absorb or scatter harmful sun radiation. Some researchers assumed that melanin protects against skin cancer.

While high UV radiation can cause skin cancer, the development of cancer usually occurs after child-bearing age. As natural selection favours individuals with traits of reproductive success, skin cancer had little effect on the evolution of dark skin.

Previous hypotheses suggested that sunburned nipples impeded breastfeeding, but a slight tan is enough to protect mothers against this issue.

A study examined the effect of sunlight on folate —a vitamin B complex—levels. The study found that even short periods of intense sunlight are able to halve folate levels if someone has light skin.

Low folate levels are correlated with neural tube defects, such as anencephaly and spina bifida. UV rays can strip away folate, which is important to the development of healthy foetuses.

In these abnormalities children are born with an incomplete brain or spinal cord. Nina Jablonski , a professor of anthropology and expert on evolution of human skin coloration, [33] found several cases in which mothers' visits to tanning studios were connected to neural tube defects in early pregnancy.

She also found that folate was crucial to sperm development; some male contraception drugs are based on folate inhibition. It has been found that folate may have been the driving force behind the evolution of dark skin.

As humans dispersed from equatorial Africa to low UVR areas and higher altitudes sometime between , and 65, years ago, dark skin posed a disadvantage.

Light skin pigmentation protects against vitamin D deficiency. It is known that dark-skinned people who have moved to climates of limited sunlight can develop vitamin D-related conditions such as rickets , and different forms of cancer.

The main other hypotheses that have been put forward through history to explain the evolution of dark skin coloration relate to increased mortality due to skin cancers, enhanced fitness as a result of protection against sunburns, and increasing benefits due to antibacterial properties of eumelanin.

Darkly pigmented, eumelanin-rich skin protects against DNA damage caused by the sunlight. The mortality rates of melanoma has been very low less than 5 per , before the midth century.

It has been argued that the low melanoma mortality rates during reproductive age cannot be the principal reason behind the development of dark skin pigmentation.

Studies have found that even serious sunburns could not affect sweat gland function and thermoregulation. There are no data or studies that support that sunburn can cause damage so serious it can affect reproductive success.

Another group of hypotheses contended that dark skin pigmentation developed as antibacterial protection against tropical infectious diseases and parasites.

Although it is true that eumelanin has antibacterial properties, its importance is secondary to 'physical adsorption' physisorption to protect against UVR-induced damage.

This hypothesis is not consistent with the evidence that most of the hominid evolution took place in savanna environments and not in tropical rainforests.

Dark-skinned humans have high amounts of melanin found in their skin. Melanin is derivative of the amino acid tyrosine.

Eumelanin is the dominant form of melanin found in human skin. Melanin is produced in specialized cells called melanocytes , which are found at the lowest level of the epidermis.

People with naturally-occurring dark skin have melanosomes which are clumped, large and full of eumelanin. Dark skin offers great protection against UVR because of its eumelanin content, the UVR-absorbing capabilities of large melanosomes, and because eumelanin can be mobilized faster and brought to the surface of the skin from the depths of the epidermis.

Keratocytes from dark skin cocultured with melanocytes give rise to a melanosome distribution pattern characteristic of dark skin.

Due to the heavily-melanised melanosomes in darkly-pigmented skin, it can absorb more energy from UVR and thus offers better protection against sunburns and by absorption and dispersion UV rays.

Darkly-pigmented skin protects against direct and indirect DNA damage. Photodegration occurs when melanin absorbs photons.

Recent research suggest that the photoprotective effect of dark skin is increased by the fact that melanin can capture free radicals , such as hydrogen peroxide , which are created by the interaction of UVR and layers of the skin.

These qualities of dark skin enhance the barrier protection function of the skin. Solar radiation heats up the body's surface and not the interior. Furthermore, this amount of heat is negligible compared to the heat produced when muscles are actively used during exercise.

Regardless of skin colour, humans have excellent capabilities to dissipate heat through sweating. In people with naturally occurring dark skin, the tanning occurs with the dramatic mobilization of melanin upward in the epidermis and continues with the increased production of melanin.

This accounts for the fact that dark-skinned people get visibly darker after one or two weeks of sun exposure, and then lose their colour after months when they stay out of the sun.

Darkly-pigmented people tend to exhibit fewer signs of aging in their skin than the lightly-pigmented because their dark skin protects them from most photoaging.

Skin colour is a polygenic trait, which means that several different genes are involved in determining a specific phenotype. Many genes work together in complex, additive, and non-additive combinations to determine the skin colour of an individual.

The skin colour variations are normally distributed from light to dark, as it is usual for polygenic traits. Data collected from studies on MC1R gene has shown that there is a lack of diversity in dark-skinned African samples in the allele of the gene compared to non-African populations.

This is remarkable given that the number of polymorphisms for almost all genes in the human gene pool is greater in African samples than in any other geographic region.

So, while the MC1R f gene does not significantly contribute to variation in skin colour around the world, the allele found in high levels in African populations probably protects against UV radiation and was probably important in the evolution of dark skin.

This does not take into account the effects of epistasis , which would probably increase the number of related genes.

Skin pigmentation is an evolutionary adaptation to various UVR levels around the world. As a consequence there are many health implications that are the product of population movements of humans of certain skin pigmentation to new environments with different levels of UVR.

Dark-pigmented people living in high sunlight environments are at an advantage due to the high amounts of melanin produced in their skin. The dark pigmentation protects from DNA damage and absorbs the right amounts of UV radiation needed by the body, as well as protects against folate depletion.

Folate is a water-soluble vitamin B complex which naturally occurs in green, leafy vegetables, whole grains, and citrus fruits.

Women need folate to maintain healthy eggs, for proper implantation of eggs, and for the normal development of placenta after fertilization.

Folate is needed for normal sperm production in men. Furthermore, folate is essential for fetal growth, organ development, and neural tube development.

Folate breaks down in high intensity UVR. It is essential for maintaining proper levels of amino acids which make up proteins.

Folate is used in the formation of myelin, the sheath that covers nerve cells and makes it possible to send electrical signals quickly. Folate also plays an important role in the development of many neurotransmitters, e.

Serum folate is broken down by UV radiation or alcohol consumption. Dark-skinned people living in low sunlight environments have been recorded to be very susceptible to vitamin D deficiency due to reduced vitamin D synthesis.

A dark-skinned person requires about six times as much UVB than lightly-pigmented persons. This is not a problem near the equator; however, it can be a problem at higher latitudes.

Dark-skinned people having a high body-mass index and not taking vitamin D supplements were associated with vitamin D deficiency. The most prevalent disease to follow vitamin D deficiency is rickets , the softening of bones in children potentially leading to fractures and deformity.

Rickets is caused by reduced vitamin D synthesis that causes an absence of vitamin D, which then causes the dietary calcium to not be properly absorbed.

This disease in the past was commonly found among dark-skinned Americans of the southern part of the United States who migrated north into low sunlight environments.

The popularity of sugary drinks and decreased time spent outside have contributed to significant rise of developing rickets.

Deformities of the female pelvis related to severe rickets impair normal childbirth, which leads to higher mortality of the infant, mother, or both.

Vitamin D deficiency is most common in regions with low sunlight, especially in the winter. Outside the tropics UVR has to penetrate through a thicker layer of atmosphere , which results in most of the intermediate wavelength UVB reflected or destroyed en route; because of this there is less potential for vitamin D biosynthesis in regions far from the equator.

Higher amount of vitamin D intake for dark-skinned people living in regions with low levels of sunlight are advised by doctors to follow a vitamin D-rich diet or take vitamin D supplements, [22] [79] [80] [81] [82] [83] although there is recent evidence that dark-skinned individuals are able to process vitamin D more efficiently than lighter-skinned individuals so may have a lower threshold of sufficiency.

There is a correlation between the geographic distribution of UV radiation UVR and the distribution of skin pigmentation around the world.

Areas that have higher amounts of UVR have darker-skinned populations, generally located nearer the equator.

Areas that are further away from the equator and generally closer to the poles have a lower concentration of UVR and contain lighter-skinned populations.

This is the result of human evolution which contributed to variable melanin content in the skin to adapt to certain environments. A larger percentage of dark-skinned people are found in the Southern Hemisphere because latitudinal land mass distribution is disproportionate.

Different dark-skinned populations are not necessarily closely related genetically. Natives of Buka and Bougainville at the northern Solomon Islands in Melanesia and the Chopi people of Mozambique in the southeast coast of Africa have darker skin than other surrounding populations.

The native people of Bougainville, Papua New Guinea, have some of the darkest skin pigmentation in the world. Although these people are widely separated they share similar physical environments.

In both regions, they experience very high UVR exposure from cloudless skies near the equator which is reflected from water or sand.

Because it is impractical to wear extensive clothing in a watery environment, culture and technology does little to buffer UVR exposure.

The skin takes a very large amount of ultraviolet radiation. These populations are probably near or at the maximum darkness that human skin can achieve.

More recent research has found that human populations over the past 50, years have changed from dark-skinned to light-skinned and vice versa.

Only — generations ago, the ancestors of most people living today likely also resided in a different place and had a different skin color. According to Nina Jablonski, darkly-pigmented modern populations in South India and Sri Lanka are an example of this, having re-darkened after their ancestors migrated down from areas much farther north.

Scientists originally believed that such shifts in pigmentation occurred relatively slowly. The speed of change is also affected by clothing, which tends to slow it down.

The Aborigines of Australia , as with all humans, are descendants of African migrants, and their ancestors may have been among the first major groups to leave Africa around 50, years ago.

Despite early migrations, genetic evidence has pointed out that the indigenous peoples of Australia are genetically very dissimilar to the dark-skinned populations of Africa and that they are more closely related to Eurasian populations.

The term black initially has been applied as a reference to the skin pigmentation of the aborigines of Australia; today it has been embraced by aboriginal activists as a term for shared culture and identity, regardless of skin colour.

Melanesia , a subregion of Oceania , whose name means "black islands", have several islands that are inhabited by people with dark skin pigmentation.

The islands of Melanesia are located immediately north and northeast of Australia as well as east coast of Papua New Guinea. In the world, blond hair is exceptionally rare outside Europe and Southwest Asia, especially among dark-skinned populations.

However, Melanesians are one of the dark-skinned human populations known to have naturally-occurring blond hair. The indigenous Papuan people of New Guinea have dark skin pigmentation and have inhabited the island for at least 40, years.

Due to their similar phenotype and the location of New Guinea being in the migration route taken by Indigenous Australians , it was generally believed that Papuans and Aboriginal Australians shared a common origin.

However, a study failed to find clear indications of a single shared genetic origin between the two populations, suggesting multiple waves of migration into Sahul with distinct ancestries.

Sub-Saharan Africa is the region in Africa situated south of the Sahara where a large number of dark-skinned populations live.

These differences depend in part on general distance from the equator, illustrating the complex interactions of evolutionary forces which have contributed to the geographic distribution of skin color at any point of time.

Due to frequently differing ancestry among dark-skinned populations, the presence of dark skin in general is not a reliable genetic marker , including among groups in Africa.

For example, Wilson et al. South Asia has some of the greatest skin color diversity outside of Africa.

Skin color among South Indians is on average darker than North Indians. This is mainly because of the weather conditions in South Asia—higher UV indices are in the south.

A study of caste populations in the Gangetic Plain found an association between the proportion of dark skin and ranking in the caste hierarchy.

Dalits had, on average, the darkest skin. Relatively dark skin remains among the Inuit and other Arctic populations. A combination of protein-heavy diets and summer snow reflection have been speculated as favouring the retention of pigmented skin.

Earliest European colonial descriptions of North American populations include terms such as "brown", "tawny" or "olive", though some populations were also described as "light-skinned".

Native South Americans and Mesoamericans are also typically considered dark-skinned, ranking similarly to African and Oceanian populations in regards to Ala presence.

Genetic tests show significant Austronesian influence, [] theorizing that Amazonian Indians and Austronesians both diverged from common ancestor.

Indigenous Mother and daughter from the Urus islands, Peru. The preference or disfavour for darker skin has varied depending on geographical area and time.

Today, darker skin is viewed as fashionable and as a sign of well-being in some societies.

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