A mammal needs fertilized egg cells to have children, right? Not so fast. University of Bath scientists report that they're the first to successfully breed healthy mice without any fertilized eggs, instead relying on inactive embryos. The team first doused eggs in strontium chloride, which prevents them from going into a state of arrest while they're turned into embryos -- previous attempts to fool the eggs saw them die within a few days. Researchers then inserted sperm nuclei that reprogrammed the embryos, readying them for the wombs of their surrogate mothers.