Scientists have been given the go-ahead to create human-animal embryos.
The hybrid embryos will be produced by mixing human cells with animal eggs.
Controversially, the embryos will only be 99.9% human. Around 0.1% of the DNA will be from the animal.
The Human Fertilisation and Embryology Authority approved thework in principle after a public consultation found the majority of people were at ease with the research.
The decision will infuriate religious groups, who say scientists are playing God.