|MadSci Network: Genetics|
John, I'm going to go ahead and run down the list of common eye colors, and we'll deal with the hazel/light brown controversy when we get there. Since I'm on the hazel/light brown borderline myself, I'm interested in the question too. The following is from Remington's "Clinical Anatomy of the Visual System," 1st edition, published in 1998 by Butterworth- Heinemann. "Iris color depends on the cell and pigment density and on the collagen arrangement and density...If the iris is heavily pigmented, the (front) surface appears brown and smooth, even velvety, whereas in a lighter iris, the collagen (fibers) are evident and the color ranges from greys to blues to greens depending on density of pigment and collagen...In all colored irises, the two epithelial layers are heavily pigmented. Only in the albino iris do the epithelial layers lack pigment." The pigment we're discussing here is melanin, produced by little cells called melanocytes in your iris. Collagen is a structural protein in your iris, as well as everywhere else in your body. Anyway, it looks like the lightest eyes are albino, because they have almost transparent irises. The next darkest is grey, then blue, then green. As for hazel, my dictionary defines it as a reddish-yellow brown. Eyes that I call hazel usually seem to have some green mixed in with them too. True hazel eyes have an orange tint to the brown which really makes them stand out. That textbook by Remington doesn't even mention hazel, leading me to believe that the official academic opinion is that hazel is just a very light colored, orange-ish type of brown. As for distinctions between different types of browns, that's a little tricky. People with more pigment in the rest of their body, such as Africans, Indians, and Southeast Asians, have distinctively browner irises than the typical Caucasian "brown eye." People with more pigment tend to have that 'velvety' dark brown look mentioned above, while Caucasian brown eyes are usually lighter brown, or even 'hazel.' But, like hair color, there are a million shades of brown, and eyes come in all ranges from light greenish brown to almost black. If you really want to figure out the exact shade of brown eye that someone has, the best way would probably be to take them to the paint store and compare color chips! So keep looking at eyes that are brown, and you'll start noticing subtle differences. Tom
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