Bipaternal human children, though, are still far awayPhotograph: Yanchang WeiTHE CONVENTIONAL way of making babies is no secret: a father produces a sperm which, when it comes into contact with a mother’s egg, gives rise to an embryo containing genetic material from both parents. The process is popular but not universally accessible; same-sex couples cannot produce biological children together. Scientists have therefore long sought more ambitious recipes, especially ones that remove the need for...