Evolution of the eye...

How could the complex human eye have evolved through natural selection acting o­n small variations?

The complex structure and mechanism of the eye is often the focus of attack by those wishing to invoke the 'intelligent design' argument. The critics argue that something so complex as the eye could not have possibly be the result of random mutations and natural selection. They argue that none of the individual components of the eye enables vision to be possible.  

This is indeed a challenge for Darwin's theory of evolution. Yet, scientists have shown that there are scenarios by which, over a long period of time, a complex mechanism as the eye can evolve.
In a pbs video a scientist explains how a simple light-sensitive pigmented spot o­n the skin can undergo a whole number of changes to evolve into the complex structure and operation of  the eye.

Indeed, the eye as exists today does have its faults!  This would not have been the case had it been the result of 'intelligent design' . Blood vessels running o­n the surface of the retina can cause problems with vision when they leak. This is often the case with people with diabetes or high blood pressure. It would have been better if they had been behind the retina, to avoid such complications.

There is a whole range of assorted 'eyes' in living species today, which provide evidence of various stages of evolution of the complex stages of development of the human eye.

Scientists have estimated that the time needed for the development of   a eye as complex as a human eye would o­nly require approximately 364 thousand years.

More details of how the eye could have evolved is located on the PBS website :

 Evolution of the Eye  :  http://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.html

Further resources o­n evolution can be found o­n the www.pbs.org website at  

http://www.pbs.org/wgbh/evolution/library/index.html

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