RE: What Use Is Half an Eye? Or no eye at all?
September 12, 2011 at 5:30 pm
(This post was last modified: September 12, 2011 at 5:50 pm by Anomalocaris.)
As a matter of fact, we can witness almost every stage of the evolution of the eye from mere light sensitive pigments in single celled blue green algea, to eye spots, to eye pits, to eye pits that almost close over to form a pin hole eye that can form images, to eyes where the pin hole is further developed to feature a focusing lens. We can further tell that the complex eye is not only possible to evolve, but easy enough to evolve such that it evolved independently in different classes of animal several times. We know this because although complex eyes are functionally similar, their fundamental structure bespeaks of several different heritage.
I like a particular example showing how easily eyes can evolve. In this case, a shrimp - Rimicaris exoculata - possesses compound eyes expected from arthopods in its youth for the purposes of seeing where it is going while swimming in the water column. But in its adulthood, it descends to the depth near hydrothermal vents, where normal levels of light doesn't exist and conventional compound eyes becauses useless. Here the adult shrimp reobsorbs its compound eye to make use of the neutrients that went into making the now surplus eye. The shrimp is now devoid of normal eyes.
But here is where it gets freaky. There is in fact extremely dim light near the hydrothermal vents, supplied by the heat of the vent water. The light is so dim that the most advanced night vision goggles used by the military need to be specially modified to see it. Those with expertise in photography knows that the light sensitivity of any optical instrument is proportional to its apperture. Each compound eye has an maximum aperture defined by the size of its lens. This aperture is too small to catch sufficient light for the shrimp to use its eye, hence the reobsorption of the compond eye.
BUT, while one could make the aperture bigger by making each lens bigger, the biggest of all aperture is no lens whatsoever, a completely naked retina is more light sensitive than any possible structured eye at the expense having literally no resolution. And this is indeed what Rimicaris exoculata developes after lossing its normal, compound, complex eye. The exoskeleton on its back developes a flat, sheet like, totally exposed, naked retina. An entire half of the exosketon forming two of the simplest eyes with infinite aperture, and no lens of any kind. Imagine this, a creature that sees with its shell because its shell is a retina.
This is not all. Light shining on a flat sheet of retina without any focusing mechanism whatsoever falls on all parts of the retina equally, as a result a flat retina has no spacial resolution whatsoever. That is to say if Rimicaris exoculata had completely flat retina flaps it can tell if light is coming from the upper hemisphere hecause its eyes are on its back, but it has no way at all of knowing which part of the upper hemisphere the light is. In other words, it has no directional resolution. But this is not good enough. How could a naked, exposed retina without any focusing aid gain directional resolution? That's it, the retina containing shell curls up. But curling up the retina, parts of the retina cast a shadow over the rest of the retina. Consequently, light from some direction would fall on only part of the retina, and not the rest. Presto, primitive, very coarse direction resolution, but directional resolution.
Now notice the more the retina flap curls, the greater the directional resolution. In Rimicaris exoculata the retina curles up to give its flap eye nearly twice the resolution of a flat retina sheet. Ie Rimicaris exoculata can tell not only if the light is coming from above or below, but also ahead or behind. But Rimicaris exoculata's retina flap never quite curl to the point of coverging again over itself. But in the nautilus it does. The retina flap curls all the way around on all sides until the edges nearly, but not quite, meet at the top, leaving only a slit to admit light. Presto, pin hole eye.
A pin hole eye has substantially more resolution still. Instead of known that there is a hue only caste by blond hair coming from in front, behind, above or below, A good pin hole eye would be able to tell if the blond has nice figure, although you might be somewhat fuzzy about her features.
Next step, evolve a transparent tissue body to refract the incoming light. Easy? Sure. The pin hole eye in the nautilis is really a hollow open sphere of retina with sea water washing freely in and out of the pupil. But it is a small step to fill the hollow retina sphere with a protective clear fluid. From thereon, evolving a segregated body of fluid that aids in light refraction is but a process of trial and error.
But what reward if the trial succeeds. Nautilis's relative octopus did precisely that. It put a organic lens behind the slot in the curled up retina of the nautilis. Presto, complex eye.
See, we know, yet creationist moron revel in the dilusion that we don't.
I like a particular example showing how easily eyes can evolve. In this case, a shrimp - Rimicaris exoculata - possesses compound eyes expected from arthopods in its youth for the purposes of seeing where it is going while swimming in the water column. But in its adulthood, it descends to the depth near hydrothermal vents, where normal levels of light doesn't exist and conventional compound eyes becauses useless. Here the adult shrimp reobsorbs its compound eye to make use of the neutrients that went into making the now surplus eye. The shrimp is now devoid of normal eyes.
But here is where it gets freaky. There is in fact extremely dim light near the hydrothermal vents, supplied by the heat of the vent water. The light is so dim that the most advanced night vision goggles used by the military need to be specially modified to see it. Those with expertise in photography knows that the light sensitivity of any optical instrument is proportional to its apperture. Each compound eye has an maximum aperture defined by the size of its lens. This aperture is too small to catch sufficient light for the shrimp to use its eye, hence the reobsorption of the compond eye.
BUT, while one could make the aperture bigger by making each lens bigger, the biggest of all aperture is no lens whatsoever, a completely naked retina is more light sensitive than any possible structured eye at the expense having literally no resolution. And this is indeed what Rimicaris exoculata developes after lossing its normal, compound, complex eye. The exoskeleton on its back developes a flat, sheet like, totally exposed, naked retina. An entire half of the exosketon forming two of the simplest eyes with infinite aperture, and no lens of any kind. Imagine this, a creature that sees with its shell because its shell is a retina.
This is not all. Light shining on a flat sheet of retina without any focusing mechanism whatsoever falls on all parts of the retina equally, as a result a flat retina has no spacial resolution whatsoever. That is to say if Rimicaris exoculata had completely flat retina flaps it can tell if light is coming from the upper hemisphere hecause its eyes are on its back, but it has no way at all of knowing which part of the upper hemisphere the light is. In other words, it has no directional resolution. But this is not good enough. How could a naked, exposed retina without any focusing aid gain directional resolution? That's it, the retina containing shell curls up. But curling up the retina, parts of the retina cast a shadow over the rest of the retina. Consequently, light from some direction would fall on only part of the retina, and not the rest. Presto, primitive, very coarse direction resolution, but directional resolution.
Now notice the more the retina flap curls, the greater the directional resolution. In Rimicaris exoculata the retina curles up to give its flap eye nearly twice the resolution of a flat retina sheet. Ie Rimicaris exoculata can tell not only if the light is coming from above or below, but also ahead or behind. But Rimicaris exoculata's retina flap never quite curl to the point of coverging again over itself. But in the nautilus it does. The retina flap curls all the way around on all sides until the edges nearly, but not quite, meet at the top, leaving only a slit to admit light. Presto, pin hole eye.
A pin hole eye has substantially more resolution still. Instead of known that there is a hue only caste by blond hair coming from in front, behind, above or below, A good pin hole eye would be able to tell if the blond has nice figure, although you might be somewhat fuzzy about her features.
Next step, evolve a transparent tissue body to refract the incoming light. Easy? Sure. The pin hole eye in the nautilis is really a hollow open sphere of retina with sea water washing freely in and out of the pupil. But it is a small step to fill the hollow retina sphere with a protective clear fluid. From thereon, evolving a segregated body of fluid that aids in light refraction is but a process of trial and error.
But what reward if the trial succeeds. Nautilis's relative octopus did precisely that. It put a organic lens behind the slot in the curled up retina of the nautilis. Presto, complex eye.
See, we know, yet creationist moron revel in the dilusion that we don't.
