Gearhart understands some people have moral objections to destroying early embryos to get their "pluripotent" cells - blank slates capable of replicating indefinitely, and spinning off all types of more mature cells.
But he also knows researchers are far from understanding pluripotency well enough to harness its healing power.
For example, Gearhart said, it has become clear that "embryonic stem cells are states, not entities."
Even though they exist only briefly in a hundred-cell embryo, they play a molecular symphony, chemically cueing some genes to play, while silencing others. If the cells are removed early in the symphony, they are different than at the end.
No wonder some embryonic stem cell colonies, or "lines," replicate well in lab dishes, while most lines morph unpredictably into more specialized cells, or die.
These barely understood genetic cues are also complicating the discovery that specialized cells, such as skin cells, can be reprogrammed to regress to a pluripotent state - no embryos needed.
"Induced pluripotent stem cells," or IPS, tend to revert to, or at least recall, their original specialty, Gearhart said. (It's like forcing a pastry chef to be a short-order cook; he can't resist substituting crepes for pancakes.)
IPS cells gradually lose this memory, but not until they have replicated many times, becoming truly blank slates.
"The technology to detect all these changes "is not easy," Gearhart said. With so much to discover, it's time to end the legal ambiguity.