The Other Stem Cell Debate

Except for the three million human brain cells injected into his cranium, XO47 is just an average green vervet monkey. He weighs about 12 pounds and measures 34 inches from the tip of his tail to the sutured incision on the top of his head. His fur is a melange of black, yellow and olive, with white underparts and a coal-black face. Until his operation, two days before I met him, he was skittering about an open-air enclosure on the grounds of a biomedical facility on the Caribbean island of St. Kitts. Afterward, he was caged in a hut shared with half a dozen other experimental monkeys, all of whom bore identical incisions in their scalps. Judging from the results of previous experiments, the human neural stem cells inserted into their brains would soon take hold and begin to grow, their fibers reaching out to shake hands with their monkey counterparts. The green vervets' behavior was, and will remain, all monkey. To a vervet, eye contact signals aggression, and when I peered into X047's cage, he took umbrage, vigorously bobbing...