'Synthetic Sperm' Grown From Stem Cells

British scientists announced they have created synthetic human sperm for the first time, the Guardian reports. The sperm—grown in a lab from stem cells—swim, have tails, and exhibit many of the same biological characteristics of real sperm, according to researchers. They believe the breakthrough could lead to a better understanding of male infertility and its treatment.

"This is an important development as it will allow researchers to study in detail how sperm forms and lead to a better understanding of infertility in men—why it happens and what is causing it," said the lead reseracher. Other scientists, however, questioned the findings, saying that they were not convinced the cells the research created could accurately be called sperm. (More embryonic stem cells stories.)