Scientists grew early-stage human kidneys inside pig embryos and found the kidneys were “structurally normal” and made up of around 60% human cells.

Scientists have successfully grown a human organ inside another animal for the first time.  In a new study published Thursday (Sept. 7) in the journal Cell Stem Cell, researchers inserted human stem cells into genetically tweaked pig embryos. When these were implanted into surrogate pig mothers, the embryos developed early-stage human kidneys within about 28 days. The research is still in its infancy, but the authors say this technology could one day help relieve the shortage of human organs needed for transplantation.