by Gregg Easterbrook

About the author: Gregg Easterbrook is a senior editor of the National Review and the author of A Moment on the Earth: The Coming Age of Environmental Optimism.

For John Gearhart, a biologist at Johns Hopkins University, professional life had been an exercise in slamming against walls. Gearhart’s specialty is Down’s syndrome, triggered when one of the infant body’s chromosomes copies itself once too often. Gearhart had spent 20 years trying to puzzle out this genetic error. “All our data suggested that Down’s was caused by something that happens quite early in embryo genesis,” he says—but the only way to find out what happens then would be to conduct experiments on human embryos, a prospect repugnant at best. Trying to think...