Wednesday, 25 March 2015

Seeing Evidence Of Inept Design

Müller cells separate between wavelengths to improve day vision with minimal effect upon night vision : Nature Communications : Nature Publishing Group

Although they will probably deny it, even creationists must be aware of the inept design that is the vertebrate eye where the retina is wired backwards, so the nerves from the photoreceptor have to travel towards the source of light then across the surface of the retina to join up with the main optic nerve and finally back down through the retina, causing the 'blind spot' - an area of the retina where light doesn't register.

Our neural circuitry has to infill this area for us so we don't notice it. Consequently, there is a small risk that we won't notice pieces of grit, small flies and other foreign bodies that get in our eyes, and the nerves going in the 'wrong' direction inevitably create a barrier for the light to get through.

In effect, the photoreceptors are are actually shielded by their circuitry. It's like the designer of a digital camera putting all the wiring and processors between the lens and the detector. Creationists call this 'intelligent'.

The strange thing is that other orders such as cephalopods, which have a basically very similar eye, don't have this problem because their retina is wired the right way round and consequently is a lot more efficient. As evidence of inept design this takes some beating and is a major embarrassment for creationists/IDiots because not only should their magic designer have got it right in the first place but they hate having to explain why it apparently invented the eye at least twice and used the worst design for it supposed favourite creation - humans.

Now a science-based article is doing the rounds and being presented as evidence that the eye isn't wired the wrong way round after all, much to the jubilation of creationists. The paper was originally published in Nature Communications in January 2014 but is now being syndicated as an article by one of the authors, Erez Ribak, which appears to suggest the eye was wired backwards for a reason. This would appear to be an extraordinary claim for a biologist and not one that would normally get past peer review into a respected scientific journal.

The 'reason' claimed seems to be so a work-around to the problem could be 'designed' in the form of Müller cells which appear to filter out the blue light and concentrate the red and green range of the spectrum on the rods - the rods being the cells responsible for colour vision, as opposed to the cones which register light and dark. The claim is that this gives improved vision.

But it only gives improved vision in the sense that it overcomes, to some extent, the faulty wiring problem by providing optical channels through the mass of nerve fibres. There is no way to improve a sharply focussed image made from light passing through a perfectly transparent medium. It only needs improving if it's been degraded in the first place:

Before arriving at the cones and rods, light must traverse the full thickness of the retina, with its layers of neurons and cell nuclei. These neurons process the image information and transmit it to the brain, but until recently it has not been clear why these cells lie in front of the cones and rods, not behind them. This is a long-standing puzzle, even more so since the same structure, of neurons before light detectors, exists in all vertebrates, showing evolutionary stability.

Researchers in Leipzig found that glial cells, which also span the retinal depth and connect to the cones, have an interesting attribute. These cells are essential for metabolism, but they are also denser than other cells in the retina. In the transparent retina, this higher density (and corresponding refractive index) means that glial cells can guide light, just like fibre-optic cables.

Whether or not the fact that Erez Ribak is not a biologist but a physicist with the Department of Physics, Technion — Israel Institute of Technology, and so might be excused for assuming a reason for apparent design, or whether there is some other motive for what appears to be this subtle misrepresentation of the science is a matter for speculation but it looks suspiciously like something designed to feed the creationist disinformation machine. But maybe I'm too sensitive in this respect.

Certainly, the original paper made no such claim, or even an implication, that the vertebrate eye is wired that way round for a purpose. The clear implication in the abstract is that the function of the Müller cells is to get light from the surface of the retina through to the photoreceptors with minimal loss and minimal distortion due to scattering:

Vision starts with the absorption of light by the retinal photoreceptors—cones and rods. However, due to the ‘inverted’ structure of the retina, the incident light must propagate through reflecting and scattering cellular layers before reaching the photoreceptors. It has been recently suggested that Müller cells function as optical fibres in the retina, transferring light illuminating the retinal surface onto the cone photoreceptors. Here we show that Müller cells are wavelength-dependent wave-guides, concentrating the green-red part of the visible spectrum onto cones and allowing the blue-purple part to leak onto nearby rods. This phenomenon is observed in the isolated retina and explained by a computational model, for the guinea pig and the human parafoveal retina. Therefore, light propagation by Müller cells through the retina can be considered as an integral part of the first step in the visual process, increasing photon absorption by cones while minimally affecting rod-mediated vision.

This explanation is of course entirely consistent with the evolutionary explanation of biological form and entirely inconsistent with an intelligent design model which would not have needed a work-around for an easily avoided problem and the failure to apply a solution already designed for a different class of animals. Perhaps the best way to put this was by the lead author of the original paper, Amichai Labin: "We finally understand how our eyes compensate for the strange, upside-down architecture of the retina." [My emphasis]

Thanks to Facebook user Kastriot Musliu for pointing me to this article.

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