Inserting human stem cells into monkey brains risks giving animals human-like qualities, says a high-level US panel after a year-long study. It agreed that this experiment was unlikely to change animals in “morally relevant ways”, but felt that “the risk of doing so is real and too ethically important to ignore”. Some of these experiments are currently under way and the panel was unable to agree which of them should proceed. A report from the panel of 22 experts, including primatologists, stem cell researchers, lawyers and philosophers, was published in the July 15 issue of the journal Science.

“Many of us expected that, once we’d pooled our expertise, we’d be able to say why human cells would not produce significant changes in non-human brains,” said the report’s lead author Mark Greene, formerly of Johns Hopkins University and now a professor at the University of Delaware. “But the cell biologists and neurologists couldn’t specify limits on what implanted human cells might do, and the primatologists explained that gaps in our knowledge of normal non-human primate abilities make it difficult to detect changes. And there’s no philosophical consensus on the moral significance of changes in abilities if we could detect them,” he added.