THE EYES OF VERTEBRATES
Why Intelligent Design?
On November 24, 2009--the 150th anniversary of Charles Darwin's On the Origin of Species
--the theory that new species can arise from old ones through natural selection is still met with some resistance. (Related: "FUTURE HUMANS: Four Ways We May, or May Not, Evolve."
Some of evolution's most vocal critics are proponents of "intelligent design," arguing that many structures in plants and animals bear the unmistakable signature of design by a supernatural intelligence.
Intelligent design proponents say the eyes of vertebrates--including humans and the common snapping turtle seen above--could not have evolved in a stepwise fashion. That's because the eye is made of several interacting parts, and the removal of any one part will cause the entire system to cease functioning. Thus, the argument goes, the eye must have been produced in one fell swoop.
"If you look at these [evolutionary] schemes, they often very abruptly add a lens or a cornea," said Casey Luskin, a spokesperson for the Discovery Institute, a Seattle-based organization that advocates intelligent design. But things don't just appear suddenly in evolution, Luskin said. "You need to evolve things in a step-by-step fashion." (Take a Darwin quiz
Evolutionists Argue ...
Steps in the evolution of the vertebrate eye exist in the fossil record, said Don Prothero, a paleontologist at California's Occidental College and author of Evolution: What the Fossils Say and Why It Matters.
"There've been multiple, very well-documented papers showing how complex structures like the eye can evolve in gradual steps from a simple eye spot that is just barely a light receptor all the way to things like the human eye," Prothero said. Intelligent design advocates, he said, simply ignore the evidence.
(See "Was Darwin Wrong?"
from National Geographic
Photograph by George Grall, National Geographic Stock