The eyes in the human being are one of the most developed organs of the entire body, with a complexity that follows the brain -which would occupy the first place- and the entire nervous system. Both are the first to develop in the embryo during gestation.
On this occasion, we will focus on a specific aspect of the eyes, their color. Melanin is the pigment responsible for eye color. and is located in the iris of the same. Its hue is brown, however we know that there is a wide spectrum of eye colors, why is it? In this article we are going to explain it to you and you will have the opportunity to know Curious and interesting facts about the colors of the eyes.
Eye color is genetically determined
Eye color is determined by the genes we inherit from our parents.. However, our eye color is unique and this is due to the phenomenon of genetic recombination, which makes our color unrepeatable on the entire planet. Yeah, there is no one in the whole world who has eyes the same color as you. Genetic recombination allows a kind of "random mix" of the eye color of your parents, giving a unique and unrepeatable result.
El gene that determines eye color is designated as OCA2 and is located on chromosome 15. It is in charge of synthesizing the pigment melanin -What is it brown or brown– in melanocytes (melanin-producing cells) and determines the color of the skin, hair and eyes.
How is it possible the existence of so many eye colors when melanin is brown?
It depends on its presence or absence, as well as its distribution in the iris. Blue or green eyes, for example, lack melanin, and brown eyes, in all their variety, have different amounts of melanin as well as a different distribution in the iris.
There is a factor that explains this phenomenon, the ICR: is a factor that indicates the distribution of melanin in the iris and provides us with information about the color of the eyes.
This distribution also influences the iris pattern that -like the color- it is unique to each person. So much so, that technology has developed the recognition of the iris pattern as a measure of digital identification, since it is a unique print in the same way that a fingerprint is.
Types of eye colors: causes and characteristics
Brown
It is the most common color and we find it in approximately 50% of the population. It dominates over blue or green, and is more abundant than these. It is due to the presence of melanin, brown or brown pigment What gives this color to the iris?
Black
It should be said that there is no black melanin, that this is a brown pigment and only brown. What gives the “black” hue is the high pigment density in the iris which makes it blend with the pupil, from which it is indistinguishable. usually has it african population, where the great concentration of pigment turned out to be an advantage in the ancestors compared to the high radiations of the continent. The "black" look is only had by less than 1% of the African population, most of them tend to be very dark brown.
Sometimes the black color of the eyes is due to a disease, the aniridia, which is characterized by the total or partial absence of the iris, so that only the pupil, which is black, would be visible. It may be caused by a genetic abnormality, trauma, or surgical complications.
BLUE
It is owned by 8% of the population and It is believed that its origin is located in a common ancestor African who, upon migrating to Europe, suffered a mutation in the OCA2 gene that would hinder your body's ability to synthesize melanin. In those regions with less radiation, the change was favorable and that would explain the persistence of the trait to this day.
Therefore, it is estimated that all the people with blue eyes in the world share this common ancestor and we are talking about a figure of 150 million.
Blue eyes, technically they are colorless, and it seems that this color it is due to the incidence of light in the layers of the iris that is reflected towards the outside, similar to the effect produced by the blue color of the sea and the sky.
Some peculiarities of blue eyes
- The low proportion of melanin has its consequences: since blue eyes contain less melanin than brown, green or hazel eyes, people with blue eyes are more sensitive to light and are at increased risk of retinal damage. This is so because the receptors are saturated by not having the filter that would provide melanin, which in sufficient quantities, protects the eye from radiation by absorbing electromagnetic waves.
- However, people with blue eyes have an advantage over the rest, and that is that see better in the dark. As they have a low amount of melanin, they reflect light very little and consequently all the incident light source that reaches them is usable, so in low irradiance conditions they maximize the efficiency of light reception.
As you see, there are many curious and interesting facts about the colors of the eyes that will continue to surprise you in the following lines.
Verde
It is the least frequent color, only 2% of the world population has it, so it would be one of the rarest eye colors.
The most curious thing of all is its origin: you may be surprised to know that the color of green eyes arose in asia and that would explain why in countries like Afghanistan there are a large number of people with green eyes. In Europe we find them mainly in countries like Hungary or Iceland and It occurs mostly in women.
amber or hazelnut
If green is a rare color, amber or hazelnut is even more so, being represented by only 1% of the world population. It is one of the colors that most nuances They present and is especially visible when it is hit by direct sunlight (which does not mean that the light changes their color, it is a frequent myth).
They may contain a mix of green and brown and sometimes they even seem yellows like those of some wolves. Without a doubt, it is one of the most fascinating eye colors that exist and gives the face a very peculiar aesthetic.
Grey
Another rarity of the nature. Gray eyes are present in less than 1% of the world population. It is a mixture of red tones with blue reflections and usually appears in albino people..
Albinism is a condition characterized by the complete absence of melanin all over the body. The eyes of albinos lack melanin and consequently the red color of the capillaries is reflected on a bluish background that projects the iris in the absence of pigment. The result is a purplish or gray color.
But gray tones of eyes have also been seen in people who are not albinos and it is also explained by a combination of low melanin and bluish reflection of the fundus. An example of this case is found in the eyes of the famous Elisabeth Taylor.
RED
As we mentioned in previous lines, this is a color that occurs fundamentally in albino people and is the result of the total absence of melanin in the iris that puts revealing the capillaries of the retina. These can be seen with the naked eye by the light that passes through them and reflects the red of the blood.
The reddish color is therefore due to hemoglobin, which is the pigment that gives blood its red color. We talk about a reddish color, not red like that of laboratory mice, for example, which in humans would be almost phantasmagorical.
More curious and interesting facts about the colors of the eyes
Some babies are born with blue eyes that later darken, why?
On many occasions, babies are born with bluish or grayish eyes and after a few months they surprise us with a change to brown. The explanation is found once again in the melanin pigment.
Babies when they are born have a good part of their immature structures, one of them is the eyes, both in appearance and in function. Newborns do not have a definitive eye color, in the same way that they see very poorly -blurry- and are colorblind; they only perceive their closest environment, which is their mother and other relatives.
These babies with apparent blue eyes have a very low concentration of melanin in their iris and as with blue-eyed adults, light reflects off the back of the eye in a similar way as it does on the sea, resulting in that bluish appearance. As they approach 6 months of age, they will generate melanin and their eye color will reach the final tone.
Do you know what heteronomy is?
Heterochromia defines that condition in which a person (or animal, where it also occurs) has one eye of each color (total heterochromia) or the same eye of two colors equally or asymmetrically (partial heterochromia).
It is due to a genetic abnormality or an injury after birth. This is the case of the British singer David Bowie who had the misfortune of suffering an injury to one of his eyes.