Any engineer would naturally assume that the photocells would point towards the light, with their wires leading backwards towards the brain. He would laugh at any suggestion that the photocells might point away from the light, with their wires departing on the side nearest the light. Yet this is exactly what happens in all vertebrate eyes. Each photocell is, in effect, wired in backwards, with its wires sticking out on the side nearest to the light. This means that the light, instead of being granted an unrestricted passage to the photocells, has to pass through a forest of connecting wires, presumably suffering at least some attenuation and distortion
Blindguide: Richard Dawkins
http://en.wikipedia.org/wiki/The_Blind_Watchmaker
Tuesday, May 29, 2007
Monday, May 28, 2007
"A Silly Design"
The vertebrate retina is a prime example of historically quirky “design”. The vertebrate retina is backwards because the development of the retina was first elaborated in rather small chordates, where issues of acuity and blind spots were non-existent; all subsequent vertebrates got stuck with this “design”.
"Imagine taking a pane of glass, then smearing it thickly with vaseline, then wiping a tiny hole in the vaseline. That is what the vertebrate retina is like."
"The vertebrate eye does very well indeed, but it is a kludge. The fovea is a cute trick to squeeze greater acuity out of a flawed design, but octopi and squid do it better."
"This is pretty silly, with the current arrangement, the photoreceptors have a range of ganglion cells, supporting cells, nerve cells and blood vessels already piled thickly on top of it (when you look into the eye with and ophthalmoscope, you can see the superficial blood vessels on top of the retina, there are also capillaries that dive deep into the cell layer as well. The retina already has a mass of blood, and lots of other things, getting in its way. Of course there is a better way to do it, the way cephalopods do it."
Blindguide: Ian Musgrave, Panda's thumb
http://www.pandasthumb.org/archives/2006/11/denton_vs_squid.html
"Imagine taking a pane of glass, then smearing it thickly with vaseline, then wiping a tiny hole in the vaseline. That is what the vertebrate retina is like."
"The vertebrate eye does very well indeed, but it is a kludge. The fovea is a cute trick to squeeze greater acuity out of a flawed design, but octopi and squid do it better."
"This is pretty silly, with the current arrangement, the photoreceptors have a range of ganglion cells, supporting cells, nerve cells and blood vessels already piled thickly on top of it (when you look into the eye with and ophthalmoscope, you can see the superficial blood vessels on top of the retina, there are also capillaries that dive deep into the cell layer as well. The retina already has a mass of blood, and lots of other things, getting in its way. Of course there is a better way to do it, the way cephalopods do it."
Blindguide: Ian Musgrave, Panda's thumb
http://www.pandasthumb.org/archives/2006/11/denton_vs_squid.html
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