Khan
English
12 May 2013
Why there are Different Colored Eyes The world is comprised of thousands of different people all over the world. One of the most significant ways in which people differ is through the color of their eyes. The majority of people in the world have brown eyes that vary from light to dark shades. People who have a European background vary even more with a wide range of brown eye colors as well as hazel, green, blue and gray. People usually learn that eye color is just a simple genetic trait where brown dominates over blue and green eye colors. However, it is not that simple. There are many genes that contribute to giving the eye its color, but eye color actually comes from a pigment called melanin, which is produced by cells in the iris. Melanin also gives hair and skin its color. When melanin levels increase, this causes a person’s skin to tan when they spend too much time in the sun. There are two types of melanin that are contained in within the skin, hair, and eye cells. Eumelanin is brownish-black pigment and pheomelanin is a reddish-yellowish pigment. Different eye colors are caused by the amount and ratio of the two types of melanin in the outer layer of the iris. Generally, darker eyes have overall more melanin and a higher ratio of eumelanin whereas lighter colored eyes have overall less melanin and higher ratio of pheomelanin to eumelanin. In brown eyes, the eumelanin absorbs light causing the iris to look brown but since blue eyes do not have much melanin, light is not absorbed. Instead the light passes into the deeper layers of the eye where it is scattered by proteins and the light eventually reflects back through the iris appearing as blue to others. This is the same phenomenon that makes the sky look blue. Other eye colors such as amber, hazel, and green have melanin contents somewhere between that of blue and brown eyes. These intermediate colors come from a combination of melanin absorbing the light and the deeper layers of the eye reflecting and scattering the light. Sometimes on certain occasions, one might notice that their eye color looks different and may believe that it is changing. However, that is not the case. The eye color being observed in oneself or another is because of the interaction of light with the eyes. This means that the eye color you see changes depending on the lighting conditions. Babies’ eyes can change color. Many infants are born with blue eyes that later darken in during their first year of life. This occurs because the melanin in the iris takes a while to build up. As mentioned before, brown is the most common type of eye color in the world. Hazel eye color or brownish red is also a common eye color and is very common among people in the U.S and