Flaw in mammalian ear is price paid for hearing ability

Science News : Researchers studying mouse embryos have found that the cells forming the tiny bones of the mouse’s middle ear are also responsible for forming a less-than-ideal lining to protect the area from infection. In what has been termed a rupture-repair process, the middle ear starts as a pouch of tissue that bursts and allows neural crest tissue to enter and form tiny bones. In mature mammals, those bones transfer sound by jiggling against the ear drum. The same tissue that forms the bones also repairs the rupture, however. Lacking the hairlike cilia of the rest of the middle ear, the neural crest tissue instead provides a bald patch that is more prone to infection. Nevertheless, the three ear bones that form in the middle earâmdash;a feature unique to mammalsâmdash;are responsible for mammals’ sensitivity to sounds. Looking for a similar rupture-repair process in marsupials has been proposed to possibly determine an evolutionary link.