One of the standard arguments creationists like to through up against evolution is the complexity argument. They make claims that some aspects of life are irreducibly complex. They claim organs such as the eye are so complex that there is no reasonable path for them to evolve along. Remove anything from it and you have a nonfunctional organ with no reason to have evolved.
Well scientists have discovered an itermediary in the evolution of the eye. Reported here it comes in the form of a Jellyfish.
http://www.newscientist.com/channel/life/mg18624995.700DARWIN famously wrote in On the Origin of Species that the eye is so complex that its evolution by natural selection seems "absurd". The key to the puzzle, he argued, was to find eyes of intermediate complexity in the animal kingdom that would demonstrate a possible path from simple to complicated. Now, a detailed study of the eyes of the box jellyfish (Tripedalia cystophora) has thrown up one of these fascinating intermediate stages.
Box jellyfish, or cubozoans, are bizarre, highly poisonous predators (New Scientist, 8 November 2003, p 34). "These are fantastic creatures with 24 eyes, four parallel brains and 60 arseholes," says Dan Nilsson, a vision expert from the University of Lund in Sweden.
The eyes occur in clusters on the four sides of the cube-like body. Sixteen are simply pits of light-sensitive pigment, but one pair in each cluster is surprisingly complex, with a sophisticated lens, retina, iris and cornea, all in an eye only 0.1 millimetres across.
The lens structure is unusual because the refractive index - the extent to which it bends light - is graded from one side to the other. Because the image is focused way behind the retina, it appears blurry. So cubozoan eyes are good for spotting large, stationary objects, while filtering out unnecessary detail such as plankton drifting with the current. From here it would be an easy step to evolve an image-forming eye.