In a remarkable—if likely controversial—feat, scientists announced today that they have created the first successful human-animal hybrids. The project proves that human cells can be \_21\_ into a non-human organism, survive, and even grow inside a host animal, in this case, pigs. This biomedical advance has long been a dream for scientists hoping to address a critical \_22\_ of donor organs. Every ten minutes, a person is \_23\_ the national waiting list for organ transplants. And every day, 22 people on that list die without the organ they need. What if, \_24\_ relying on a generous donor, you could grow a custom organ inside an animal instead? That's now one step \_25\_ reality, an international team of researchers led by the Salk Institute reports in the journal Cell. The team created what's known scientifically as a chimera: an organism that contains cells from two different species.