In a controversial step that raises the possibility of a new kind of infertility treatment, scientists report that they have produced functional human eggs in the lab that were able to be fertilized with sperm. The proof-of-concept study, published today in the journal Nature Communications, involves using human skin cells to generate eggs, some of which were capable of producing early-stage embryos. None of the embryos were used to try to establish a pregnancy, and it’s unlikely that they would have developed much further in the womb. It could also be used to help same-sex couples have genetically related babies by creating eggs from male cells and sperm from female cells. To make the eggs, researchers transplanted the nucleus of a human skin cell into a donor egg that had been stripped of its nucleus—the cell’s control center that houses its genetic material.