From the first cell division to the promise of regenerative medicine, embryology is entering a new era, one that forces us to rethink where science should stop. Where should society draw the line between innovation and respect for human life? Artwork by Cory Sever Every human life begins in a moment so small it is almost abstract: a single fertilized cell. But that cell does not simply “unfold” into a body. It divides, again and again, multiplying into a growing population of cells that...