Can anyone explain how an evolutionary leap like eyes occur?

Question

How does a creature go from no eyes to having a complex organ like an eye? does the creature realize that it needs to see when no other creature in history has ever done so, and then just will it to be?

I can understand how other senses came into play as they are just extensions of nerve sensitivity. Taste, touch and hearing but to create an organ like an eye when none has ever been before seems like a HUGE leap. Why would a creature develop the structure if it had no idea that future generations could use it? Take into account that it would have to create a socket for it first and then develop the muscle and fluid filled sac with specific cones for different colors.

It would have to have happened when we were supposedly still fish as the tree branches after that organ is in full use.

I am only looking for reasoned thought as this is a serious question. If you respond with insults or stupidity, you will be reported.

Answer 1

Why is the eye different from any other sense?  Light sensitivity is common in many organisms including plants and protists.  The ability to detect light and shadow can provide an increase in reproductive efficacy.  Over many many many generations natural selection may act on variants of this light sensing mechanism (just like it has done for taste, touch, smell, and hearing) and modify it to increase the detection of light.  Small modifications can have profound effects on the light sensing mechanism.  A lens would concentrate weak light, an aperture would regulate light amounts, different receptors would allow the detection of color.  

That the eye evolved is without question.  In fact it evolved several times.  The compound eye of an insect is fundamentally different from a mammalian eye and the eye of an octopus is also an example of convergent evolution in that the orientation of the retina is reversed allowing it superior light sensitivity.

Answer 2

I think you'll find the wikipedia article very informative.

http://en.wikipedia.org/wiki/Evolution_o...  be sure to check the references!

Answer 3

It's a good question, and I'll try to answer it as best as I can.

It wasn't as big a leap as you think.  You're right, that the other senses are just modifications of nerves, but the eyes are no different.  The eye would have started out as an eye spot - basically a patch of photosensitive nerves.  These eye spots would be unable to form images, but could steer the organism towards light or away from predators (if there were predators large enough to cast a shadow at this point in time).

After that, it's simply a matter of increasing the density of the proto-retina and building up a protective structure around it.  This structure is believed to have started out as a simple cup of tissue.  This cup would have allowed simple aiming of the eye as well.  Eventually, it got to the point where the surrounding tissue had almost closed around the retina.  The small hole that was left would have acted as a lens without the need for an actual lens, using the same principles involved in a pinhole camera.  There are actually some species that survive to this day using a pinhole lens in their eye (most notably, the nautilus).

Unfortunately, a pinhole lens still would have left the eye open and vulnerable.  The cornea would have evolved at first as a thin sheet of tissue over the opening, and would have gradually cleared up to give better vision (the first proto-cornea probably would have been a tradeoff - protection at the expense of some vision).  The lens could have come about through simple duplication of the cornea, followed by specialization.

I think you misunderstand evolution a little bit, though.  Thought doesn't enter into the process of evolution.  The first creatures to develop eyes didn't do so by a feat of will.  They simply developed a random mutation that happened to be beneficial and gave them a better chance of survival.  Each future modification of the eyes occurred in exactly the same manner, with imperceptible revisions with each generation.  That's why, even in a species with a short generational time, it would have taken millions of years to make significant progress.

As for the future generations, these modifications aren't always useful, and sometimes it isn't apparent until much later.  If you look at an evolutionary tree, you'll see many dead ends.  These often occur because a species becomes over-specialized to a certain niche, but then natural climate change eliminates the niche, and the species along with it.  Take the dinosaurs for example.  They were supremely adapted to their environment at the time.  Then came along the giant impact, which drastically changed the climate.  The dinosaurs had been very well suited to their climate, but were unable to survive the low temperatures and scarce food following the impact (they were too specialized to their environment to adapt to the changes).

Answer 4

It didn't evolve all at once; it developed from simple light-sensitive patches on the surface of single-celled organisms, through gradual changes of complexity. The answer to the creationist question "What good is half an eye?" Is, "quite a lot when the other option is no eyes at all." Here's a site with a summary and a video to explain it:

Answer 5

Our eyes didn't evolve in a one-shot, they are a series of developments.

Your problem is that you are trying to imagine it forming as a whole, rather than as a series of parts.

It's like looking at a book, and not seeing the chapters, the paragraphs, the sentences, the words and finally the letters and punctuation symbols used to construct the book as a whole.

Answer 6

The evolution of the eye is known from studies in comparative anatomy, paleontology and molecular biology.  Rather than a leap, it was a series of small discrete steps, each of which was adaptive.  First step was a single nucleotide copying error that led to a body cell making an opsin protein that was sensitive to light.  From there to several light sensitive cells grouped together near the head of the organism.  From there to the light sensitive cells being grouped in an indentation of skin.  From there to a deepening of the indentation = eye cup.  From there to a narrowing of the top of the eyecup = pinhole effect, a crude lens.  From there to clear cells at the top of the pinhole = true lens, etc., etc.

The earliest adaptations were in detecting light/dark, then movement, then crude shapes.  Sight as we know it did not evolve until much later.

Answer 7

It wasn't a leap, it was a gradual process building over eons, each kingdom or phyla taking something from it's progenitors.

http://blog.case.edu/singham/2007/07/30/...

http://www.d.umn.edu/~olse0176/Evolution...

http://www.pbs.org/wgbh/evolution/librar...

http://www.karger.com/gazette/64/fernald...

http://www.corante.com/loom/archives/200...

http://www.talkorigins.org/faqs/vision.h...

http://www.medilexicon.com/medicalnews.p...

http://www.stephenjaygould.org/ctrl/futu...