Get ready for the great stem cell debate to flare up once again: Researchers at the Newcastle University in England reported that for the first time, they have successfully extracted sperm cells from embryonic stem cells, Time magazine reports. While these cells aren’t suitable for implantation—which British law prohibits—they could be used as an important tool in researching male infertility. Normal sperm development, stem-cell bioethicist Insoo Hyun said, takes more than 15 years and isn’t easily observable—but the in vitro-derived sperm (which can only come from male embryos) would only take three months to mature. So, what’s next? Potentially, infertile men could grow sperm in a lab and regain the ability to father children. “We have the potential therapeutic use of a technology that pushes the boundaries of what people feel comfortable with ethically,” Hyun said.