Allegations about the proper treatment of lab animals may take on strange new meanings as scientists work their way up the evolutionary chart.
First, human stem cells were injected into bacteria, then mice and now sheep. Such research blurs biological divisions between species that couldn't until now be breached.
Drawing ethical boundaries that no research appears to have crossed yet, the National Academies recommend a prohibition on mixing human stem cells with embryos from monkeys and other primates.
But even that policy recommendation isn't tough enough for some researchers.
"The boundary is going to push further into larger animals," New York Medical College professor Stuart Newman said. "That's just asking for trouble."
CNN.com - Creating 'human-animals' for research - Apr 29, 2005