Scientists Debut Lab Models of Human Embryos

Carl Zimmer writes in The New York Times: In its first week, a fertilized human egg develops into a hollow ball of 200 cells and then implants itself on the wall of the uterus. Over the next three weeks, it divides into the distinct tissues of a human body. And those crucial few weeks remain, for the most part, a black box. "We know the basics, but the very fine details we just don't know," said Jacob Hanna, a developmental biologist at the Weizmann Institute of Science in Israel. Dr. Hanna and