Blue, gray, green, brown, dark brown – how many people in the world, so many shades of the color of the irises. Where do they come from and do they depend only on the distribution of pigment in the iris? What else affects eye color?
- The main reason is melanin
- Why does frequent exposure to sunlight not cause a change in shade?
- Genetic factors
- Is it possible to have eyes of different colors?
- What do the experts say about this?
- Research
- Research on the relationship between the nature and shade of the iris
- Dark (black, brown) eyes
- Green eyes
- Grey eyes
The main reason is melanin
The shade is directly dependent on the content of melanin pigment – a dye that is present in the skin in different amounts in different people. The color of the skin and the possibility of a quick or slow tan, hair color, the number of moles on the skin and just the color of the eyes depend on it. The stronger the concentration of the dye, the darker this shade.
Dark-haired people often have a dark iris, therefore, they have dye in large volumes, blondes and redheads have it many times less. In addition to the aesthetic issue, which manifests itself in the coloring of the skin and hair, melanin performs an additional function — it receives ultraviolet rays (this is the cause of sunburn). When it comes to the shade of skin and hair, this dependence is very simple; somewhat different rules rule in the matter of eye color. Nature often shows that eye and skin color do not always go together.
In addition to the content of pigments in the iris, the density of the cells of the stroma of the iris affects the shade of the eyes. In turn, the density of iris stroma cells determines how much light the main pigment of the epithelium absorbs.
Why does frequent exposure to sunlight not cause a change in shade?
The pigment in the organs of vision has completely different properties than in the skin. When a person is often exposed to the sun, there is not the slightest chance of changing the color of the eyes from lighter (blue) to darker (brown or dark brown). And the point here is that the protective mechanisms of these organs do not create opportunities for the influx of ultraviolet rays into these sensory organs (nature gave a person a reflex to lower his eyelids in bright light).
In addition, the cornea concentrates the sun's rays, does not allow them to pass through the entire iris. Otherwise, it would carry the risk of damage to the light-sensitive structures in the eye and loss of its ability to function normally.
Genetic factors
Heredity plays a big role in determining the shade of the iris. Brown-eyed people will in all cases have dark-eyed heirs, or (more rarely) they may have a green-eyed child. Individuals with blue irises are capable of having both light-eyed and green-eyed children. This happens due to the inheritance of genes that determine the formation of the desired amount of dye in the iris. And the color of the baby's eyes changes after the first six months of his life. So it is necessary that he gradually produces the desired amount of pigment. The hue gradually changes to a darker one.
Is it possible to have eyes of different colors?
Of course, you don't see this very often. Just like the uneven distribution of the dye in the eyes (brown around the pupil, and blue on the rest of the iris). This is not considered a sign of a disease, although it can often be a sign of genetic abnormalities and may predispose to the development of diseases of the organs of vision in the future. Only a professional who has subjected the sense organs to research is able to refute such risks.
Several genes have an influence on the shade of the iris. Their combinations lead to the appearance of different shades or colors that are difficult to unambiguously identify.
The simplified theory of eye color inheritance that people learn in school suggests that when the dominant gene takes over, the person tends to have dark eyes, and when the recessive gene, they tend to have blue eyes. If the father has a recessive gene and a dominant one, then there is a 50% chance that the offspring will have dark or light eyes. If both parents have blue eyes, their child will not have dark eyes. Such a couple has two recessive genes, and, therefore, they cannot pass on dominant genes to the child.
What do the experts say about this?
In fact, this shade is due to the amount of melanin and the ratio of eumelanin (dark brown dye) and pheomelanin (reddish dye). The OCA2 and HERC2 genes play the most important role in determining the color of the iris, but in addition to those listed, at least 10 other genes are known to affect this characteristic. Ultimately, the interaction of all of them determines the final result. Thus, parents with blue eyes can have children with brown irises. All babies are born with blue eyes. Eye color usually stabilizes around the sixth month of life.
Research
In 2006, the molecular basis of EYCL3 was analyzed. Studying a group of 3,839 people, the scientists found that 74% of all eye color variations could be explained by single nucleotide polymorphisms (SNPs) in the OCA2 gene, which, if mutated, can cause albinism. Recent studies have shown that SNPs have a strong association with blue and green eyes, freckle count, hair and skin tone.
Eye color is found in different variations from black tones to sky blue. Seeing the need to standardize a classification system that was simple yet detailed and easy to research, anthropologists developed a grading system based on identifying the dominant hue in the iris. First of all, the presence of brown and yellow pigment is taken into account.
It is assumed that people with a certain dominant eye color live in certain geographical areas of the world. For example, Asians have very dark eyes, while typical Slavs are blue or grey. Sometimes it's hard to tell what someone's eye color is. It changes with the lighting.
One scientific explanation also suggests that purple eyes are associated with people with albinism. They are born with a lack of pigment in the skin, hair and iris of the organs of vision. Lack of pigmentation causes their eyes to take on a purple-blue or red tint.
Research on the relationship between the nature and shade of the iris
Scientists have made more than one attempt to prove that the shade of the eyes indicates certain personality characteristics. They found out whether the color of the iris partly determines certain behaviors. Scientists from Sweden explain that the eye has many neurological connections with the brain and therefore there may be an unusual combination of iris color with character.
Dark (black, brown) eyes
It is assumed that people with dark eyes — they are born leaders. Even if they don't realize it, others more often intuitively sense a strong personality in them. The dark color of the iris means that there is a large amount of melanin in the body, and, therefore, much more energy. The genes of black-eyed people allow them to overcome more disasters, and their brains work more efficiently and faster. There are also some cryptic sayings.
Interestingly, it has been proven that people with dark eyes need less sleep than others, but it is much more difficult to get up in the morning. An additional feature is a well-developed self-confidence and the ability to be pleasant to others.
Green eyes
This is the rarest and most unique shade. According to studies, the green shade of the iris is considered the sexiest and very attractive to the people around. There are only a few people with a green tint, they are considered to be outstanding and very smart.
They are usually calm, although they have a lot of energy and are very creative. They are not afraid of lack of time. They can be good and responsible friends and faithful partners for life. Although they are usually calm, they can indulge in a little madness and extravagance.
Green irises are recognized as the result of the presence of a small to moderate amount of melanin, which makes them look like blue eyes in close light with small dots of a different shade of color distributed over the iris. Blue and brown together make green, but no green pigment. If the amount of pigment increases a little, it can cover the blue. If the pigment covers the blue completely, the eye may turn brown. Green irises are not common, but are most common among Europeans, in particular among the Irish and residents of northern European countries. Among European Americans, green eyes are most common among those of Germanic ancestry.
Grey eyes
They are the prerogative of creative individuals who have a strong personality but a sensitive soul, ambitious and able to cope with any situation. They approach everything with great responsibility, do not rest on their laurels, constantly strive to give all the best more and more. They are very imaginative and creative.
Persons with gray eyes may be courageous in their professional lives, but have problems with courage in their personal lives. Often they are loners, isolated from others and cannot decide on a lasting relationship, because they show too much caution in the relationship between a man and a woman.
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