What our eyes have different color, everyone knows. But not everyone understands why this is so. The fact that the color of our eyes is responsible for the pigment melanin contained in the iris of the eye. The more of his body, the darker the iris. That is, if a person has completely black eyes, so he has a lot of melanin, if a blue or green – a little.
It happens that a person's eyes different colors. This phenomenon is called heterochromia. The difference in color appears due to the shortage (excess) of melanin. This phenomenon occurs both in humans and in animals (cats). Heterochromia is of two kinds: full and partial. Complete heterochromia occurs in cases when the color of the iris is completely different from the color of the "iris" of the other eye. Partial heterochromia is very rare, about 4 people out of 1 million, then one part of the "iris" is different from the remaining part, i.e. one eye combines the two colors.
Generally eye color is largely determined by heredity. It is known that the Earth is more dark-eyed people, since a large amount of melanin is the dominant characteristic and, therefore, often inherited. So if one parent has brown eyes and the second blue or green, the probability that the child will be blue-eyed are at a minimum.
It is also interesting that the color of the eyes change during life. All children are born with blue eyes – in their body yet not enough melanin. When the pigment accumulates, they become the desired color. To old age some people eyes can become bright due to the fact that the mesodermal layer becomes less transparent.