THE eye has long been an evolutionary battleground. Ever since William Paley came up with the watchmaker analogy in 1802 鈥� that something as complex as a watch must have a maker 鈥� creationists have used it to make the 鈥渁rgument from design鈥�. Eyes are so intricate, they say, that it strains belief to suggest they evolved through the selection and accumulation of random mutations.
Recently, evolutionary biologists have turned this argument on its head. They say that the 鈥渋nside out鈥� vertebrate retina 鈥� curiously structured so that its wiring obscures the light sensors and leaves us with a blind spot 鈥� can be described as one of evolution鈥檚 鈥済reatest mistakes鈥�.
The anatomy of the retina is indeed good evidence that eyes were cobbled together bit by bit. Surely a creator would never have chosen to construct an eye in this way. In return, creationists have argued that the backwards retina clearly has no problems providing vertebrates with excellent vision 鈥� and even that its structure enhances vision.
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This week, a study by (non-creationist) neurophysicists in Israel has found just that (see 鈥淥ptical fibre cells transform our weird, 鈥榖ackward鈥� retinas鈥�). Their simulations showed that M眉ller cells, which support and nourish the neurons overlying the retina鈥檚 light-sensitive layer, also collect, filter and refocus light, before delivering it to the light sensors to make images clearer.
Of course, findings that coincide with the claims of creationists do not mean they have a point 鈥� although they may well quote this study. Intelligent design proponents have shown themselves to be adept at speciously quoting peer-reviewed studies that appear to support their claims.
鈥淭he findings do not mean the creationists have a point 鈥� although they may well quote the study鈥�
Sure, sending light through M眉ller cells enhances vision, but that is not an argument for choosing to put the wiring in front of the sensors. It still creates a blind spot, where the nerves dive through the light-sensitive cells on their way to the brain.
It would make much more sense to put M眉ller-like cells in front of the sensors, with the wiring behind. Rather than provide evidence in support of intelligent design, the new work is actually yet another example of evolution鈥檚 extraordinary ability to create workaround solutions to problems arising from earlier iterations.
Kenneth Miller, a biologist at Brown University in Providence, Rhode Island, and an untiring veteran of the creation-evolution wars, calls the M眉ller cells 鈥渁 retrofit: a successful and highly functional adaptation made necessary by the original architecture of the retina, but a retrofit鈥�. The eye鈥檚 structure, and the blind spot in particular, bears the unmistakable fingerprints of Darwinian evolution.