It’s usually better to worry too soon than too late about an ethical quandary, but the National Institute of Health is thinking far in advance when it expresses concern about scientists attempting to grow human organs in lab animals. It’s not that the NIH believes such experiments are bad for the creatures–that would be understandable–but the agency wants to halt the research because it feels injecting human cells into other species may invest them with a human level of understanding. It’s really difficult to believe that’s happening anytime soon.

In a MIT Technology Review report, Anthony Regalado reports that numerous American labs are pushing forward on this front despite threats of funding being pulled. An excerpt:

The experiments rely on a cutting-edge fusion of technologies, including recent breakthroughs in stem-cell biology and gene-editing techniques. By modifying genes, scientists can now easily change the DNA in pig or sheep embryos so that they are genetically incapable of forming a specific tissue. Then, by adding stem cells from a person, they hope the human cells will take over the job of forming the missing organ, which could then be harvested from the animal for use in a transplant operation.

“We can make an animal without a heart. We have engineered pigs that lack skeletal muscles and blood vessels,” says Daniel Garry, a cardiologist who leads a chimera project at the University of Minnesota. While such pigs aren’t viable, they can develop properly if a few cells are added from a normal pig embryo. Garry says he’s already melded two pigs in this way and recently won a $1.4 million grant from the U.S. Army, which funds some biomedical research, to try to grow human hearts in swine.

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The worry is that the animals might turn out to be a little too human for comfort, say ending up with human reproductive cells, patches of people hair, or just higher intelligence. “We are not near the island of Dr. Moreau, but science moves fast,” NIH ethicist David Resnik said during the agency’s November meeting. “The specter of an intelligent mouse stuck in a laboratory somewhere screaming ‘I want to get out’ would be very troubling to people.”•