Wednesday, 24 December 2014

Fossil Fish Refutes Another Creationist Lie

Acanthodes bridgei
Image: Tanaka et al., Nature Communications
Three-hundred-million-year-old fossil fish still has traces of eye tissue | Science/AAAS | News

An amazingly well preserved fossil fish from 300 million years ago has its eyes so well preserved that it can be seen to have had both rods and cones in its retina, showing that it had colour vision. This is the first time a fossilized vertebrate eye has been found with that degree of detail and probably results from the fish becoming quickly submerged in anoxic sediment so protecting it from bacterial action.

It has also been shown to have melanin in its eyes - a pigment normally associated with good daylight and twilight vision when it's present in eyes, which would have been useful in the shallow, brackish, estuarine conditions in which it probably lived. It was found in ancient estuarine deposits near Hamilton, Kansas, USA.

Details of this find can be read in full in Genko Tanaka, et al.; Mineralised rods and cones suggest color vision of 300 Myr-old fish; Nature Communications, 23 Dec 2014, made available by Nature's laudable content sharing initiative.

The fact that colour vision was probably present in fish 300 million years ago may seem a little surprising since eyes are normally assumed to be complex organs which would take a long time to evolve to that level of sophistication, but in fact computer models using genetic algorithms have shown that eyes can evolve very quickly if the ability to see gives a graded improvement at each stage.

Creationists like to wave the eye around asking, "What's the use of half an eye?" assuming their targets will be ignorant enough to think this is an argument against gradual evolution and for intelligent design. The only problem is, there is a lot of use for half an eye, and even a quarter of an eye, if the alternative is no eye at all. Creationist quote miners will even quote Darwin when he posed the 'problem' of explaining the evolution of the eye, neglecting to inform their willing dues that he went on to say how evolution by natural selection could explain it very well in the very next paragraph.

A small patch of light-sensitive cells can detect light and dark and probably the movement of a shadow across it. A shallow pit of light-sensitive cells allows light to be gathered from a larger area like a TV dish collects radio signals. A deeper pit of cells with a small opening acts like a pinhole camera allowing an image to be formed on the patch of light-sensitive cells so allowing shapes to be detected. Adding a lens allows the depth of focus to be varied so giving vision of a greater range of distance and finally, adding additional cells which respond differently to different wavelengths of light gives colour vision. So a gradual improvement results from each small step - and we have examples of each of these to be seen in nature.

In fact from a study of comparative anatomy we can see that several different eyes have evolved over time in different orders of animals from vertebrates to molluscs and from arachnids to platyhelminths. Even green plants are able to detect and respond to light, either growing towards a light source or turning their leaves towards it.

So, to the chagrin of creationists, it really isn't at all surprising to find colour vision in a 300 million year old fish. Of course, they'll need to use one of their tradition devices to wave aside the age of this fossil and will probably need to misrepresent the science and will claim it's evidence of a global flood just a few thousand years ago, ignoring that such an act of fossil formation would have resulted in a thick single layer of fossils containing modern species, all jumbled up and from all over the globe instead of different series arranged as we see them and mostly of archaic forms or extinct species. But then creationists were never strong on facts and/or joined up logic.

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