Stem cell biologist Hiromitsu Nakauchi has been waiting for this moment for more than a decade.

After years of planning, the persistent researcher has at last received approval from a government willing to pursue one of the most controversial scientific studies there is: human-animal embryo experiments.

While many countries around the world have restricted, defunded or outright banned these ethically-fraught practices, Japan has now officially lifted the lid on this proverbial Pandora’s box. Earlier this year, the country made it legal to not only transplant hybrid embryos into surrogate animals, but also to bring them to term.