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Dark skin is the human skin color that is rich in melanin pigments, especially eumelanin. The evolution of dark skin is believed to have begun around 1. In the heat of the savannas, better cooling mechanisms were required, which were achieved through the loss of body hair and development of more efficient perspiration. The loss of body hair led to the development of dark skin pigmentation, which acted as a mechanism of natural selection against folate depletion, and to a lesser extent, DNA Dark skin asian girls. The primary factor contributing to the evolution of dark skin pigmentation was the breakdown of folate in reaction to ultraviolet radiation ; the relationship between folate breakdown induced by ultraviolet radiation and reduced fitness as a failure of normal Dark skin asian girls and spermatogenesis led to the selection of dark skin pigmentation.

By the time modern Homo sapiens evolved, all humans were dark-skinned. Humans with dark skin pigmentation have skin naturally rich in melanin especially eumelaninand have more melanosomes which provide a superior protection against the deleterious effects of ultraviolet radiation. This helps the body to retain its folate reserves and protects against damage to the DNA. Dark-skinned people who live in high latitudes with mild sunlight are at an increased risk — especially in the winter — of vitamin D deficiency.

As a consequence of vitamin D deficiency, they are at a higher risk of developing ricketsand numerous types of cancers, and possibly cardiovascular disease and low immune system activity. This is attributed as, possibly, due to lower presence of Vitamin D binding agents and thus higher bioavailability in dark-skinned individuals.

The global distribution of generally dark-skinned populations is strongly correlated Dark skin asian girls the high ultraviolet radiation levels of the regions inhabited by them. These populations, almost-exclusively, live near the equator, in tropical areas with intense sunlight: Australia, Melanesia, New Guinea, South Asia, and Africa. Studies into these populations indicates dark skin is a retention of the pre-existing high UV adapted state of modern humans before the out of Africa migration and not a later evolutionary adaptation.

Due to natural selection, people who lived in areas of intense sunlight developed dark skin colouration to protect against ultraviolet UV light and to protect their body mainly from folate depletion. Evolutionary pigmentation of the skin was caused by ultraviolet radiation of the sun. As hominids gradually lost Dark skin asian girls fur between 1.

In the tropics, natural selection favoured dark-skinned human populations as high levels of skin pigmentation protected against the harmful effects of sunlight.

Genetic evidence also supports this notion, demonstrating that around 1. 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 Dark skin asian girls of the hand and the soles of feet.

At times, individuals with more sweat glands were born. These humans could search Dark skin asian girls food and hunt for longer periods before being forced back to the shades. The more they could forage, more and healthier offspring they could produce, and higher the chance they had Dark skin asian girls 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 Dark skin asian girls of Dark skin asian girls 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 asian girls skin.

Previous hypotheses suggested that sunburned nipples impeded breastfeeding, but a Dark skin asian girls 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 Dark skin asian girls 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 Dark skin asian girls can strip away folate, which is important to the development of healthy foetuses. In these abnormalities children are born with incomplete brain or spinal cord.

Nina Jablonskia professor of anthropology and expert on evolution of human skin coloration, [33] found several cases in which mother's visits to tanning studios were connected to neural tube defects in early pregnancy.

She also Dark skin asian girls that folate was crucial to sperm development; some male contraception drugs are based on folate inhibition. It has been found that folate may have Dark skin asian girls the driving force behind the evolution of dark skin. As humans dispersed from equatorial Africa to low UVR areas and higher altitudes sometime betweenand 65, years ago, dark skin posed as 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 ricketsand different Dark skin asian girls 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 perbefore 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 that 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, Sri lanka nude aunty pictures importance is secondary as a physical absorbed to protect against UVR induced damage. This hypothesis is not consistent with the evidence that most of the hominid evolution took place in savanna environment and not in tropical rainforests.

Dark-skinned humans have high amount 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 melanocyteswhich 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. 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 radicalssuch as hydrogen peroxidewhich are created by the interaction of Dark skin asian girls and layers of the skin. These qualities of Dark skin asian girls skin enhance the barrier protection function of the skin. Solar radiation heats up rather the Dark skin asian girls surface and not the interior. Furthermore, this amount of heat is negligible compared the heat Dark skin asian girls 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, Dark skin asian girls 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 Dark skin asian girls 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 Dark skin asian girls number of polymorphisms for almost all Dark skin asian girls 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. According to Abasi Ene-Obong, the founder and CEO of biotech start-up 54gene, black Africans and people of black ancestry are more genetically diverse than all of the other populations in the world combined, making their genetic information a huge resource to be tapped.

He has set up a genetic research laboratory in Nigeria's largest city of Lagos in order to analyse 40, DNA data samples and develop treatments for some diseases, keeping the needs of dark-skinned people in mind.

This does not take into account the effects of epistasiswhich 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 Dark skin asian girls, 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 intense UVR. It is essential Dark skin asian girls 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.

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.


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