A couple of years ago Jennifer Doudna had a nightmare about a gene-surgery tool called Crispr-Cas9, the revolutionary discovery that made her name. She was asked to explain it to a man sitting in the next room.

When she opened the door, this man turned out to be Adolf Hitler, but with the face of a pig. “I want to understand the uses and implications of this amazing technology you have developed,” he said.

He is not the only one. Days after researchers in the UK published the results of the most effective use of Crispr-Cas9 on human embryos yet, Professor Doudna is losing sleep over what their findings might mean for the future of our species…