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Why are Africans darker and Europeans whiter?
About 60,000 years ago, following Homo erectus, Homo sapiens also left tropical Africa and came to Eurasian temperate regions with higher latitudes or weaker ultraviolet rays. Their original black skin was not conducive to their health and survival, because temperate regions The sunlight is relatively weak, and the ultraviolet rays are not as strong as those in the African tropics. If a person’s skin color is too dark, it will block the penetration of weak ultraviolet rays, so that the human body cannot absorb enough sunlight to synthesize vitamin D, resulting in deficiency and a series of diseases.
As a result, people in temperate regions have slowly evolved lighter skin to allow ultraviolet rays to penetrate their skin.
The world can be divided into three regions:
(1) Tropical
(2) Subtropical and temperate zones
(3) The Arctic and Antarctic Circles above 45 degrees latitude
In the tropics, UV rays are strong year-round, and people can synthesize vitamin D year-round.
In subtropical and temperate zones, there are at least one month of the year when UV rays are not sufficient. For example, the Boston area of the United States, located at regarding 42 degrees north latitude, has insufficient sunlight in winter, and human skin can only start producing vitamin D following mid-March every year.
As for the Arctic and Antarctic circles, ultraviolet rays are generally not sufficient for the body to synthesize vitamin D for most of the 12 months of the year.
This can explain why people in the tropics generally have black skin. In the tropics, there is sufficient sunshine, and people do not have vitamin D deficiency problems.The reason why they evolved dark skin is not to synthesize vitamin D, but to block strong ultraviolet rays from destroying the body’s folic acid。
“Light skin tone” allows people to synthesize enough vitamin D!
In subtropical and temperate regions, ultraviolet rays have a seasonal shortage, especially in autumn and winter, which is not conducive to the human body to synthesize enough vitamin D, so the dark skin of the primitive species gradually evolved into a lighter color, so that more Ultraviolet rays penetrate deeply.
Because the sunlight in subtropical and temperate regions is not as strong as in the tropics, people in these regions do not need tropical dark skin to protect the body’s folic acid. Light skin tone is just right, it can synthesize more vitamin D without destroying folic acid.
In the same way, people in the Arctic and Antarctic circles have less sunlight, and the body’s folic acid is not in danger of being damaged by ultraviolet rays. Their problem is that if the skin color is still black like the native African human, then this African black will block weak ultraviolet rays from penetrating, and the human body cannot produce enough vitamin D, so they need to evolve a relatively white skin color.
Melanin in dark skin acts like a natural sunscreen that protects tropical people from folic acid and protects their skin from sun-induced skin cancer.
Conversely, in temperate regions and regions near the Arctic and Antarctic circles, where there is less sunlight than in the tropics, the less people need this melanin sunscreen. If they have too much melanin, it’s not good for them to synthesize vitamin D in areas with low sunlight, so they evolve whiter and whiter skin tones.
Why are the Inuit people living in the North Pole darker?
Is this model of skin evolution applicable everywhere?
Generally speaking, accurate. But there are several situations that seem to be “not allowed”, but are actually worthy of further discussion.
For example, in Alaska and northern Canada, near the Arctic Circle, where the ultraviolet rays are weak, the Inuit (formerly known as Eskimo) living there should have a very white skin color, but the true skin color of the Inuit is not. A little dark.
Why? There may be three reasons.
Firstthey are actually immigrants who migrated to North America only regarding 5000 years ago, not long enough for them to evolve whiter skin.
second, Inuit traditional foods, especially fish and marine mammals, are rich in vitamin D. This offsets their vitamin D deficiency from lack of sun exposure and allows them to retain their darker skin tone.
thirdIn the area where the Inuit live, although the latitude is high, there is snow all year round, and the reflected ultraviolet rays are strong, and they need darker skin protection.
At high latitudes, sunlight and UV rays are generally weak, such as Sweden in northern Europe, but there are exceptions, such as Inuit snow. Another example is the Qinghai-Tibet Plateau and the Andes High Mountains in South America, which belong to the temperate zone, so people’s skin should be relatively white, but these two places have high altitudes and strong ultraviolet rays, so people’s skin is darker.
Evolution takes a long time to accumulate: they are immigrants from the color of their skin!
In southern Africa, between latitudes 20 and 30 degrees south, there are two large groups of peoples: the Khoisan and the Zulu, both of which are very different in skin color. The Khoisan have light brown skin, while the Zulu have dark black skin.
Why are the skin colors different in the same sunshine area?
It turned out that both were immigrants, originating from the equatorial tropics of Africa, but the Khoisan migrated to southern Africa as early as 150,000 years ago. Their skin color, which should have been a tropical dark black, has slowly turned to a light brown following 150,000 years of evolution.
However, the Zulu people migrated to southern Africa only regarding 2000 years ago, and the evolutionary time is too short, so the skin color has not changed much, it is still dark black.
In the same way, today in the United States and many European countries, there are many African-Americans whose skin color is still black, which is not in line with the weaker ultraviolet rays in the local area. It is precisely because they are all immigrants. Since the 17th century, white Americans and Europeans, The large number of black slaves imported from Africa are only a few hundred years old at most.
If given enough time (such as tens of thousands of years later) and appropriate ecological changes, the skin color of blacks in these temperate regions may also turn white.
After black immigrants immigrated to the United States: vitamin D deficiency in black Americans
In 2009, shortly following Obama took office, the American paleoanthropologist Nina Jablonski, who specializes in the study of human skin color, said in a speech with a smile that President Obama had “slightly dark brown skin”. , “Let’s wish him good health, and may he be aware of his own skin color.” This means that Obama should take more vitamin D supplements, because his dark skin may not allow the faint North American sunlight to penetrate his skin. The skin needs to synthesize enough vitamin D, not to mention that he works indoors for a long time and has little chance to be exposed to sunlight.
We don’t know if Obama is deficient in vitamin D, or if there are additional supplements. However, according to a 2006 study by the USDA’s Human Aging Nutrition Research Center at Tufts University in Boston, black Americans are indeed more deficient in vitamin D than other Americans.
Most young, healthy blacks do not achieve optimal 25-(OH)D levels at any time of year. 25-(OH)D is the main storage form of vitamin D in the body. Detecting 25-(OH)D can tell if the body has enough vitamin D. Researcher Susan Harris pointed out that this is mainly the melanin in black skin, which blocks sunlight and reduces vitamin D production.
But blacks have lower fracture rates than other Americans. It might be that they have other adaptive mechanisms in their body that protect their bones and don’t need as much vitamin D. However, vitamin D not only protects bones, it also protects once morest cardiovascular disease, diabetes and certain cancers, which blacks suffer from as much or more than whites.
Finally, the study encourages blacks to increase their vitamin D levels or take supplements because of the low cost, low risk and high health benefits.
Are women lighter skinned? Is it for courtship, or to conceive offspring?
There is also a common feature of human skin color – in populations around the world, women’s skin color is generally always lighter than that of men, between regarding 3% and 4% lighter.
Scientists often theorize why, but most believe that the phenomenon stems from what Darwin said“Sexual selection” (sexual selection), that is, men prefer to choose women with lighter skin to be their sexual partnersso that the whiter women are easier to find a mate, can breed more offspring, have a better survival advantage, and finally eliminate those women with darker skin.
But Mustobronsky believes that sexual selection may only be part of the reason. The real reason is,Women need more vitamin D throughout pregnancy and lactation to get calcium from food. So women have evolved lighter skin tones than men so that they can absorb more UV rays from the sun to produce vitamin D.
This can be a challenge in the tropics, because in places with a lot of sun, the skin cannot be too light – too light the sun will destroy human folic acid, but too dark skin, the penetration of sunlight is not enough, and the production of vitamin D may not be enough to meet the needs of pregnancy and lactation.
Women’s skin tones, more often than men, need to maintain a delicate balance.
Different skin colors in humans have important biological functions, not for “beauty” or other “superficial” reasons.
The skin looks simple in structure, but it is the largest organ of the human body – the skin of the human body weighs 4 kilograms.
Skin color is essential to human health and survival. Humans need to evolve different shades of skin tones to synthesize vitamin D and protect folic acid in the human body in areas with different strengths of ultraviolet rays, otherwise health will be poor. Human skin color changes with the intensity of ultraviolet rays in different regions, and it also shows that humans are a species with a high degree of adaptation and evolution, so that they can survive in almost every ecological environment in the world.
– This article is excerpted from “Where did man come from: six million years of human evolutionJune 2022,Times Publishing please do not reprint without permission.
