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Evolution of the Mammalian Eye: Ho-Hum, No Big Deal?

Stephen A. Batzer

human eye.jpg

Many ENV readers will be familiar with the Nilsson and Pelger paper that purports to show how the emergence of the complex mammalian eye is no problem at all for undirected natural selection. Given the time available, it’s a trivial matter, really. Move along, nothing to see here.
The narrative has been so embedded in evolutionary thought that J.S. Turner writes in his 2007 book, The Tinkerer’s Accomplice: How Design Emerges from Life Itself, “An optical eye seems to be a fairly easy thing to evolve. Photosensitivity is not much of a big deal…Photoreceptors? A bit of a ho-hum there too. Lenses, meanwhile, are also easy to contrive.” That breezy explanation is designed to be comforting, but is it accurate?
Well, no. Nilsson, Pelger, Turner, et al., don’t have to actually sweat it out in the lab and elicit eyes from organisms using selection of the artificial or natural type, and thus cannot confirm their conjecture. They neither start with eyeless organisms, such as a flatworm, and develop photosensitive cells, nor do they select new components in creatures such as the nautilus, the eye of which, according to Dawkins, is “crying out for a lens.” Thus, the Nilsson and Pelger paper is a tour de force of unverified speculation.
Of course, it is much worse than that. Over at ENV’s friendly competitor Uncommon Descent, skeptic Vincent Torley gives a thorough treatment to this Icon of Evolution: “Could the eye have evolved by natural selection in a geological blink?” Not to be missed!
EDITOR’S UPDATE: Of course it shouldn’t be missed either that Torley’s article, as he acknowledges, derives from David Berlinski’s pioneering deconstruction of Nilsson and Pelger, in Commentary and in writing that appeared here first: “The Vampire’s Heart.” For the full Berlinski treatment, see the Discovery Institute Press book The Deniable Darwin.