It's worth noting that IVF itself, which merges sperm and egg cells in a lab, also set off debate when it debuted 35 years ago. The procedure carries some small medical risks, such as a slightly increased chance of premature and low-weight babies, and creates many embryos that never get used. But let's not forget its enormous upside: It has allowed millions of couples to have children who couldn't otherwise. Mitochondrial replacement isn't any scarier—or any less impressive. Mitochondrial disease affects only about 1 in 5,000 people. The method will be performed at a few select clinics in the U.K. and will be carefully monitored. If it proves to be safe, then thousands of women will have the option to bear healthy biological children without giving them their disease. And if it's not safe, it will most likely be banned.