On the second day of the Second International Summit on Human Genome Editing, the last session before lunch was already running long. But the crowd crammed into the Lee Shau Kee Lecture Centre at the University of Hong Kong wasn’t budging. Neither were the 5,500 people around the world glued to their live video feeds. Everyone was waiting to hear from the the final speaker, the man who says he helped make the world’s first gene-edited babies.

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