Expert: Walter Hintz - 3/28/2007

Question
Why mammals have whitesclera? Its because collagen and elastic fibers? Why have some mamals larger iris than other? Does it have any reasons in evolution of mammals?
thank you

Answer
Hi morfeus
 You are asking why questions and why questions are difficult to answer.  I sometimes shock my students by answering "Because. That's why"  Why questions deal with evolutionary biology.  Things are like they are because that is the way they evolved and that is what works best.
Why is the sclera white? True; the tissue is white. In fact if you look closely it is kind of bluish and if the eye gets irritated it gets red (bloodshot)
Why is there a difference in the size of the iris in mammals? The iris regulates the amount of light that enters the eye so it stands to reason that animals with bigger irises require more light. (like nocturnal animals) It works for them.  
Evolution tells us that things that work are the things that are retained.