Two years ago, Mike Archer from the University of New South Wales looked down a microscope and saw that a single fertilised frog egg had divided in two. Then, it did it again. And again. Eventually, the egg produced an embryo containing hundreds of cells.

“There were a lot of hi-fives going around the laboratory,” says Archer.

This might seem like an over-reaction. After all, millions of frog eggs divide into embryos every day, as they have done since before dinosaurs walked the earth. But this egg was special. Archer’s team of scientists had loaded it with the DNA of the southern gastric brooding frog—a bizarre creature that has been extinct for almost 30 years.

The fact that it started to