Why are eyes coloured?

Why are most eyes brown?

Hypothesis

Most of our eyes are coloured or brown because the irirs (the coloured part) gets its colour from our parents/genetics. We think so because lots of other human features come from our genetics (hair colour, skin tone...).

All about the Pupil and Iris

The Pupil is actually the only part of the eye that we see out of. The Iris is associated with the Pupil as they help each other out. The Pupil is very light sensitive therefor needing a point of focus. The Iris is that point. The Iris's job is to make sure that the Pupil only is exposed to a certain amount of light. The Iris opens up in darker light; creating the Pupil to get bigger, and closes the Pupil in brighter light. This takes a lot of movement, which makes the eye dry. The eye needs to stay moist otherwise foreign objects will sting in the eye, therefor making us blink. The eyelid gives off a liquid to re moist the eyes. For example if you have a staring contest with someone it may not last that long because there will begin to get dry, forcing yourself to blink and almost "windshield wipe" you eye.

So why are eyes coloured?

Like our skin, eye colour is determined by pigmentation. The iris, located behind the cornea, is made up of multiple layers. The outer two are known as the anterior border. This contains pigment-producing cells called melanocytes. Everybody has roughly the same amount of melanocytes but our genes determine how much melanin, they produce. It's the same pigment that determines skin colour and the more melanin we produce, the darker the colour.

Why so many brow eyes?

So a person with dark skin also has darker, browner eyes. Fairer skinned people produce less melanin, therefor making the colour of their eyes lighter. That's why most people have brown eyes!