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thumbnail image of human eye life's grand design

diagram of how eye forms in human embryo
In the human
embryo, eyes
develop from
bulges in the
brain's neural
tube that
pinch in to
form cavities.

Inside-out development  
Evolution, which works by repeatedly modifying preexisting structures, can explain the inside-out nature of our eyes quite simply. The vertebrate retina evolved as a modification of the outer layer of the brain. Over time, evolution progressively modified this part of the brain for light sensitivity. Although the layer of light-sensitive cells gradually assumed a retina-like shape, it retained its original orientation, including a series of nerve connections on its surface. Conversely, mollusk eyes are wired optimally because rather than evolving from brain cells, which have wiring on the surface, they evolved from skin cells, which retained their original orientation with the wiring below the surface.  
The living world is filled with examples of many other organs and structures that clearly have their roots in the opportunistic modification of a preexisting structure rather than the clean elegance of design. This does not, despite the fears of "intelligent design" advocates, amount to evidence against the existence of a Deity. Properly understood, as Darwin himself pointed out, it only deepens our respect for the power and subtlety of the Creator's remarkable ways. end of essay squid eye
Mollusk eyes
don't share the
problem" that
human eyes
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