"Thinking" machines go back as far as Pascal in the 1600s, but today's machines--computers--have reached levels of sophistication that few could have imagined just decades ago. Now, scientists are perfecting computers that can "learn" from their experiences, can create their own programs, and--perhaps--even one day "feel" emotions the way humans do. Even if we can create a computer that acts like a human, do we really want to? Will we ultimately replace ourselves with machines we create?