With advancing lab technology perhaps calling into question a longstanding guideline that prohibits experimentation on human embryos older than 14 days, scientists and ethicists gathered at Harvard Law School recently to discuss whether and how that stricture should be revised.

Some speakers at the event, held at the School’s Austin Hall on Nov. 7, urged changes that get to heart of why 14 days was once considered appropriate rather than a simple prohibition. Lifting that limit would allow scientists to learn more about human development and improve guidance on the handling of newly developed cellular structures that mimic embryos.

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“I’m terrified to ask lawmakers to pass laws, I’m terrified of what we’d get,” said Stanford University Law School Professor Henry Greely. “Probably worse than what we have now.”