This combination of microscope images provided by researchers Gianluca Amadei and Charlotte Handford in August 2022 shows natural, top, and synthetic mouse embryos with colors added to show comparable brain and heart formation. According to a study published in the journal Nature on Thursday, Aug. 25, scientists have created “synthetic” mouse embryos from stem cells without a dad’s sperm or a mom’s egg or womb. (Gianluca Amadei, Charlotte Handford via AP)