Why are human eyes different colours? Gabrielle Kuper, aged 5, London
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Readers reply
Well, eyes are different colours to give lyricists and singers half a chance of making a decent living. Would Van Morrison have had quite such a hit with Two-eyed Girl? Crystal Gayle and Don’t It Make My Eyes, Eyes? I mean, nice melody, but what is she on about? Would Frank Sinatra have filled Madison Square Garden with Ol’ Eyes is Back? bricklayersoption
Acknowledging that the author of the question is five (aww!), the many beautiful eye colours you see in your friends and family are part of who they are when they are born. An interesting fact is that some babies’ eyes change colour as they grow up. Dorkalicious
People’s eyes have different colours because light goes into them and some of the light is reflected back, just like water drops reflect the colours in a rainbow. What colour we see in someone’s eyes depends on what part of the rainbow is reflecting back. Jon (age 55)
The coloured part of your eye is called the iris. Most people have a black or brown iris, and as a result many people have black or brown eyes. In front of the iris there are several parts of the eye that can affect the colour of the light as it passes through them. This is similar to the reason that the sky is blue – the blue light is more likely to pass straight through, rather than bouncing off something. This effect, along with colour differences in other parts of the eye, can make eyes appear blue, green, grey or hazel. Very few people, like the actor Elizabeth Taylor, have eyes that are so blue they appear purple. This is also caused by light being scattered. Some people, who have a condition called albinism, cannot make in their bodies the dark substance known as melanin. Melanin is what makes the iris black or brown, so these people, as well as having very pale skin, tend to have red, pink or purple eyes. SemiFunctional
People have different amounts of pigment; more melanin gives a brown eye. Pigments cluster, so you get variations like hazel. Eye colour is defined by a particular chromosome, so it is inherited. Mary Kamaluddin
I’d guess there are different evolutionary advantages to different eye colours in different environments. Darker eyes block more light than pale eyes, so may work better in sunny countries. You see lots of brown eyes in southern Europe, whereas blue and grey eyes are more common in northern Europe, where they pose no disadvantage. An article I found says everyone had brown eyes 10,000 years ago and that everyone with blue eyes has inherited a specific genetic mutation. Astravanman
Mine are the same colour. tortinwall
