Humans and chimpanzees started their own independent evolutionary paths 7 million years ago. At that time, humans, like chimpanzees, were covered with thick hair and pink skin under it. By about1.20 thousand years ago, the skin color of ancient humans had begun to darken, which was probably the direct result of hair loss. Human hair loss is like losing protection, and mosquito bites, scratches and bruises come one after another, but the most important problem to be solved is exposure.
Light skin+sun exposure is a matter of life and death for ancient humans. The sun shines brightly during the day, and hunting in the big sun has no light and heat, so energy consumption is very fast. What is even more frightening is that ultraviolet rays will directly damage human cells and tissues, and the body can only rely on melanin to defend itself. Melanin can play a shielding role, thus protecting the skin. At the same time, the distribution and quantity of melanin determine people's skin color. In the long run, dark skin became the skin of the ancients millions of years ago? Protective color? .
This dark skin lasted for a long time. About 654.38 million years ago, the differentiated skin color of human beings began to form. Homo sapiens goes to the world, and the body is also resisting ultraviolet rays and getting vitamin D.
Vitamin d is of great significance to people. It helps people absorb calcium and other minerals, which is essential for the growth and repair of bones. However, the synthesis of vitamin D needs sunlight, and only ultraviolet rays can help chemicals synthesize vitamin D in the skin. For people who go to high latitudes, dark skin has become the biggest obstacle to the synthesis of vitamin D. Any migrating human needs to strike a balance between resisting ultraviolet rays and absorbing ultraviolet rays, so the quantity and distribution of melanin are different.
Genetic research has helped us restore the path of Homo sapiens out of Africa. About 654.38 million+years ago, climate change made Africa's resources in a hurry, and some people had to start to move toward a wider distance. With several departures, Homo sapiens spread from Africa to Europe, Asia, Oceania and America. In this great migration, the intensity of ultraviolet radiation also changes with the change of latitude and altitude, and the secretion of melanin is gradually shaped to adapt to the environment.
As mentioned above, skin color is related to the quantity and distribution of melanin. Specifically, melanin can be divided into true melanin and melanoid, true melanin is dark brown, and melanoid is red or yellow.
Scientists have found that the gene named MC 1R not only determines whether the human body can produce eumelanin and melanoid at the same time, but also regulates the content and function of these two melanoids. This gene appeared about1.20 thousand years ago, which is probably related to the darkening of human skin color after hair loss. The other two genes, HERC2 and OCA2, are associated with lighter skin color, but they are common among residents in African countries such as Tanzania. They originated 6.5438+0 million years ago, which can prove that early humans had light skin color.
So human skin evolved from light color after hair loss to dark color. Protective color? In order to avoid being harmed by strong ultraviolet rays, when Homo sapiens walked out of Africa and faced with different latitudes, altitudes and climates, the quantity and distribution of melanin changed, forming a differentiated skin color.