User: Skeletally, how do baby teeth work? They just fall out and then larger feel come down from the mouth? What is the evolutionary reason for this?
Assistant: Baby teeth, or “milk teeth”, are the first set of adult teeth to come through in early childhood.  These deciduous teeth serve different functions than adult teeth.  Milk teeth are present in children for approximately 12 years.  Typical baby teeth are smaller than adult teeth, as they are intended to serve certain important functions without wearing down too quickly.  When the adult teeth come in, the baby teeth recede and disappear, usually by the end of 6th grade.  Fewer permanent teeth typically come in during childhood than baby teeth are lost, which means that baby teeth perform specific functions in the mouth, such as eating solid foods and guiding adult teeth into position.  Human babies have 20 primary teeth, which eventually evolve into 32 permanent teeth, while a symbolic number of teeth lost or impacted during childhood typically leads to “crowded” adult teeth as adults.  Human milk teeth are helpful in providing teeth in a youthful child’s mouth, and tend to disappear naturally when the permanent adult teeth come in.