Undated photo released by U.S. Salk Institute on Jan. 26, 2017 shows a 4-week-old pig embryo containing human cells. In a bold but potentially controversial quest for solutions for the worldwide shortage of transplant organs, scientists attempting to grow human organs inside pigs have successfully grown the first chimera embryos containing cells from both humans and pigs, they said Thursday. (Xinhua/U.S. Salk Institute)
