Expert: Walter Hintz - 2/21/2007

Question
thanks!
And this scale of iris have any biological reason? It depends on something?  
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The text above is a follow-up to ...

-----Question-----
Why have humans white sclera? Because some apes and other animals have a different "color of the white of the eye".
Thank you
-----Answer-----
 Hi morfeus;
The sclera of all mammalian eyes is white.  Many mammals like apes,have very large irises and the sclera is not seen.
Why is it white?  The tissue forming the sclera has no pigment

Answer
Your question lies in the realm of evolutionary biology. Why questions are tough to answer. All characteristics of living things have a biological reason.  Basically the characteristics of the sclera (white) occur because that is what works the best when it comes to the function of the eye.  The sclera gives the eye shape and it's opaqueness blocks out all light except that which enters the pupil