Scientists injected stem cells into a pig embryo to create the first human-pig embryo.

Human stem cells about to be injected into a pig embryo.

Human stem cells being injected into a pig embryo.

This pig embryo was injected with human cells early in its development, and grew to be four weeks old.

This pig embryo was injected with human cells early in its development and grew to be four weeks old. (

This pig embryo was injected with human cells very early in its development and made it to four weeks.

This pig embryo was injected with human cells early in its development and grew to be four weeks old.

This pig embryo was injected with human cells very early in its development and made it to four weeks.

This pig embryo was injected with human cells early in its development and grew to be four weeks old.

This pig embryo was injected with human cells early in its development, and grew to be four weeks old.

This involved injection of human cells in the embryo of a pig, which then grew to four weeks old.

This involved injection of human cells in the embryo of a pig, which then grew to four weeks old.

HUMAN CELLS GROW IN PIG FETUS © Karen Kasmauski / Getty Images For the first time, scientists have succeeded in growing human stem cells in a pig embryo.

Researchers will now, for instance, be allowed to create animal embryos with a human pancreas and transplant it into the womb of a pig, which could in theory result in the birth of a baby pig with a human pancreas.

Image: Pablo Ross of the University of California, Davis inserts human stem cells into a pig embryo as part of experiments to create chimeric embryos.