All parents, Dr. Wermke said, have an innate ability to understand and respond to their babies. Indeed, it was mothers who supported her research from the beginning, even as other scientists were skeptical. In the 1980s, when Dr. Wermke first began recording babies’ sounds, many researchers viewed crying as a mere biological alarm signal, worth investigating only in the context of problems such as colic. But mothers never doubted that their tiny babies were worth studying. As Judith Fricke, little Joris’s mother, said, “I think you’d recognize the sound of your own child among a hundred others. You develop an ear for that.”