Are manners learned behavior or instinct?

Obviously, a verbal or written 'please' or 'thank you' are learned behaviors.  We're taught as toddlers to say please and thank you to EVERYONE and for EVERYTHING. We're taught these words by our parents, caregivers, relatives, teachers, and others.  This behavior is ingrained, repeated, and reinforced during an individual's early childhood.  What happens to the behavior (which later becomes identified as manners) as the child gets older is a whole different story. 

I've found myself in long awkward pauses when someone near and dear to me doesn't use their manners, I've often said, "what do you say?"  Unfortunately, I'm not able to use this same not so gentle nudge when working with the public.  If I'm asked for something or have just done something for someone, I'll provide a pause in case there is anything the person would like to say to me. I guess my instinct tells me not to pause too long.