Wednesday, December 12, 2007
The Eyes Have It!
There is a report out concerning a study of 400-million-year-old Devonian placoderms from Australia (like that handsome fellow to the right) published in the latest edition of the journal, Biology Letters of the British Royal Society. According to the report (always to be allowed some grains of salt), these extinct armored fishes provide "the first definite fossil evidence demonstrating an intermediate stage in the evolution of our most complex sensory organ," the vertebrate eye. As Dr. Gavin Young from the Department of Earth and Marine Sciences of the Australian National University put it:
The vertebrate eye is the best example of structural perfection – as used by proponents of intelligent design to claim that something so complex couldn’t possibly have evolved.Well, not quite. Although they are definitely the direct descendents of William Paley, who, along with many others, extolled the vertebrate eye as an evident product of design, modern ID creationists have moved on to newer, but not any better, targets for their "gee, that's complicated, it must be designed" arguments. Still, the news is exciting anyway:
The palaeobiologist discovered that unlike all living vertebrate animals – which includes everything from the jawless lamprey fish to humans – placoderms had a different arrangement of muscles and nerves supporting the eyeball – evidence of an “intermediate stage” between the evolution of jawless and jawed vertebrates. ...Drat the mean ol' Darwinists! They just insist on coming up with more evidence all the time!
Part of the trouble in tracing the evolution of the eye is that soft tissues don’t tend to fossilise. But the eye cavities in the braincase of these 400 million-year-old fossil fish were lined with a delicate layer of very thin bone. All the details of the nerve canals and muscle insertions inside the eye socket are preserved – the first definite fossil evidence demonstrating an intermediate stage in the evolution of our most complex sensory organ.
These extinct placoderms had the eyeball still connected to the braincase by cartilage, as in modern sharks, and a primitive eye muscle arrangement as in living jawless fish.” Dr Young said that this anatomical arrangement is different from all modern vertebrates, in which there is a consistent pattern of tiny muscles for rotating each eyeball.