In 2006 a landmark article, the British Medical Journal claimed that abortions without fetal anesthetic were okay before 26 weeks of gestation, because fetuses at five and a half months can't feel pain. That was the 2006 opinion of Dr. Stuart W.G. Derbyshire, in discussions with American literary agent John Brockman, and that article came to be a basis for many abortions. Maybe a lot of M.D.s secretly wondered if that was really true, because the history of medicine is full of bad guesses that turned out to be wrong. But we know what happens if skeptics pipe up in...