For the first time, a team of U.S scientists have grown an embryo that grows whole human organs inside pigs.
Described on Thursday in the journal Cell, the experiment involves injecting human stem cells into the embryo of a pig, then implanting the embryo in the uterus of a sow and allowing it to grow.

After four weeks, the stem cells developed into the precursors of various tissue types, including heart, liver and neurons, and a small fraction of the developing pig was made up of human cells.

As these scientists claim this revolutionary technique could be the answer to the world’s organ transplant shortage, experts have also raised ethical concerns saying organs developed in Petri-dishes are not identical to the ones that grow inside a living thing.

Dr David King, Director of Human Genetics Alert, said he finds these experiments “disturbing” as not only that pig diseases might be carried into the human population, but also there are psychological and philosophical “concerns about mixing species”.

Izpisua Belmonte, a developmental biologist at the Salk Institute and the senior author on the study of the human-pig chimera said, “We were just trying to answer the yes or no question of, can human cells contribute at all? And the answer to that question is yes.”

Nevertheless, this breakthrough is been considered by many experts as an important step in the goal to grow human organs in other animals.