Edit | corner
The planet is home to more than 8 million species, but it is we who are at the top of the species and food chains. Humans also distinguish major human races such as white, yellow, black, and brown according to skin color, but what about the color of the eyes? It is said that the human eye actually has nine colors of difference.
There are probably blacks, browns, blues, amber, browns, greens, grays, purples, and reds, which are much more colorful than we thought.
The color of the eye, which is actually the color of the iris, determines the color of the iris, which is the content of melanin. The higher the content of melanin in the matrix of the iris, the darker the color of the iris.
Brown: Brown eyes are the most common eye color in the world, we often think of ourselves as "black eyes, yellow skin" of the yellow descendants, in fact, 99.99% of Asian eyes are brown, Chinese eyes are not black, but dark brown.
Blue: Blue eyes are mainly found in Europe, especially in Iceland, Finland and other Nordic regions, and about 8% of people in the world have blue eyes. Blue eyes are blue due to insufficient precipitation of iris melanin, and light rays are scattered through the iris.
Amber: Amber eyes are common in "cats" but rarely seen in people. It is inferred that the amber eyes are caused by partial yellow fetal pigmentation. Amber eyes are found in minorities in some countries in South Asia.
Brown: About 5%-8% of people in the world have brown eyes, which at first glance looks a bit like brown, but is lighter than brown.
Green: Green eyes are the rarest, with only about 2% of the world's population having green eyes. Green eyes are mostly found in northern and central Europe, but also in some parts of Western Asia.
Gray: Gray eyes, like blue eyes, are also very little melanin in the iris, and reflect natural light, showing a gray effect. Gray eyes are second only to green in rarity and are more common in Eastern European countries.
Purple: Elizabeth Taylor is famous for her purple eyes. Purple eyes are not really purple, but have a purple effect in some light. It is speculated that it may be that the original iris is blue, because the blood vessels on the iris are more developed, and the blood color and blue scattered light are mixed, so there is a distinct purple color.
Red: Those with red or pink eyes, usually albinism. Patients with albinism "do not form" melanin because of genetic mutations, so there is no melanin in the iris, and the eyes appear red with blood vessels. Some patients with albinism have a small amount of melanin in the iris, and the eyes will be light brown or blue.
Black: We often describe "a pair of dark eyes", in fact, black eyes are relatively rare, and it is not Chinese with pure black eyes, but Costa Ricans in Latin America.
In addition to the eye color above, there are also people with heterochromatic pupils. A model named Sarah McDaniel became popular because of her unique blue and yellow pupils. This is actually a disease, iris. Congenital mydriasis is related to heredity, and men with disease-causing genes are passed on to their daughters. Acquired pupil discoloration may be lesions caused by damage to the iris. The global incidence of iris heterochromia is about 1%, congenital iris not only does not affect vision, but also greatly improves the appearance value, harvests a super high return rate, can be said to be a very "happy" disease.
The color of the human eye is actually determined by multiple genes, and the genes OCA2 and HERC2 on chromosome 15 are thought to play an important role in eye color. The OCA2 gene is responsible for the maturation of melanoids, and the HERC2 gene affects the expression of the OCA2 gene.
Melanin is a protective pigment that also determines people's skin color and hair color. Melanin is good at absorbing sunlight, which is essential for the iris, which acts to control the brightness of the light that enters the eye. Once passing through the lens of the eyeball, the visible spectrum mostly enters the retina, and the visible spectrum becomes an electrical impulse within the retina and is converted into an image by the brain. The little bit of light that the iris doesn't absorb will form a reflection, which in turn will form the color of the eye we see.
In this way, the color of the eyes depends on the type and density of melanin that a person is born with. There are currently two types of melanin: eumelanin and brown melanin. Eumelanin forms a chocolate color, while brown melanin forms a yellowish brown, green, and light russet. The formation of blue eye color is due to low true melanin content. In the case of low eumelanin stocks, eumelanin will disperse light near the anterior layer of the iris, causing this melanin to appear as a shorter wavelength of blue. This is a typical example of blue becoming a so-called "structural color". Brown – which also includes green and light russet to some extent – is defined as "pigment color". To some extent, the sky is blue.
The green color of the eyes is interesting because it is the result of the scattering of light and the combined action of the two melanins mentioned above. Green eyes have a slightly higher content of eumelanin than blue eyes, and also contain a certain amount of brown melanin. Light russet eyes originate from the same combination of melanin, except that more melanin is concentrated in the outer top layer of the iris. The more rare red and blue-purple eyes are caused by very low or complete absence of melanin. In fact, the red eye is completely devoid of melanin, so what we see is exactly the color of the blood vessels presented by reflected light. In the presence of some melanin but the content is too small to disperse the wavelength, red and blue form an extremely rare blue-violet color when they interact.
People used to think that eye color stemmed from relatively simple patterns of inheritance. But in recent years, scientists have discovered that eye color is the result of a combination of multiple genes. In addition, small variations in genes can cause different shades of the iris. Moreover, scientists speculate that Europeans did not have blue eyes 14,000 years ago, and their skin "faded" later than the eyes. About 6,000 to 10,000 years ago, the OCA2 gene that affects the formation of melanin in the European body was mutated, reducing the production of melanin, and only then did the eyes of Europeans "dilute" into blue.
Reference source: Refer to the news network Sohu.com