Hype tempts us all. It would be naive to exempt scientists from sometimes overstating the promise of their research. Early claims about what gene therapy would accomplish, for example, were arguably exaggerated and eroded public confidence. Yet claims about what stem cell research may accomplish belong in a class by themselves. The general public is now convinced that something momentous is occurring. Both professional and popular publications register the excitement that scientists evidence. This research, it is routinely said, will not only expand significantly what we know about cellular life, but it will also bring dazzling clinical benefits. Those who suffer from Alzheimer\u27s disease, Parkinson\u27s disease, and others are regularly ...