At the heart of the argument over teaching evolution in the classroom is the claim that some scientists, not just religious believers, support the concept of "intelligent design." Advocates of intelligent design argue that living things are too complex to be explained by natural forces alone. Therefore, they say, only a higher power - God or an unnamed "designer" - could create life and empower it to evolve into the myriad species of organisms on Earth today. The vast majority of working scientists contend that biological evolution is an established fact supported by overwhelming evidence. They say that evolution's mechanism...