The increasingly less elusive manimal

William Saletan wrote in favor of chimeras in the Washington Post</a> last weekend (via Eye on DNA): </p>

The Stanford experiment wouldn't actually produce a human brain. Most brain cells aren't neurons, and the experiment called for inserting human cells after the mice had constructed their brain architecture. But last year in the journal Developmental Biology, researchers proposed to insert human stem cells in mice before this architectural stage. The resulting "mouse/human chimeras," they argued, "would be of considerable value for the modeling of human development and disease in live animals."
When Stanford's ethicists first heard the proposal for humanized mouse brains, they were grossed out. But after thinking it over, they tentatively endorsed the idea and decided that it may not be bad to endow mice with "some aspects of human consciousness or some human cognitive abilities."

Hmmm....The research is certainly important, but I'm not entirely sure this is benign -- setting aside for a moment my concerns about superintelligent mice. The article doesn't mention the macaques with human brain cells. As an observer watching the trend toward higher and higher human genetic and cellular content in laboratory models, I wonder if there is any proportion that an ethics board would reject.

Sure, one theme of Frankenstein was "Don't mess with Mother Nature." But another was that sometimes society's ethical qualms are right. I wouldn't think we're at that point yet; but I'm wondering where that point is, exactly?