At the Salk Institute for Biological Studies in San Diego, Fred Gage and colleagues examine how a generic embryonic stem cell evolves into a highly specialized brain cell. Their hope is that understanding stem-cell evolution will reveal what keeps cells healthy and lead to new therapies. But federal restrictions on human embryonic stem-cell research are discouraging Gage and others. "I would say that I'm limiting my effort in this field," he says. "It's been time consuming. Resources are taken away from other things." Human embryonic studies can be conducted only with private money, creating burdens such as fundraising and setting up a separate lab with new staff, equipment, and supplies.