. >> in christian art, joseph is invarianly portrayed as an elderly gentleman. >> frank peters teaches new york university to christians, muslims and jews. >> joseph is written out of the story to preserve this virginity. not only is there a virgin conception of jesus but then mary continued to be a virgin after the birth of jesus. which means you can't have brothers and sisters. right? >> yet the gospels, according to matthew and mark, clearly mention jesus as having brothers and sisters. some church bodies, this is not an issue. after the virgin birth, mary and joseph had a conventional family. professor peters, a former priest, says roman catholics have wrestled with the question. >> that word, brothers, is sort of problematic in the life that is the question of dogma driving interpretation again. so what we have is a greek word, which the primary meaning is brother. anybody looking at that text and seeing are these not the aboyfoy of jesus would say are these not the brothers of jesus? >> the apocryphal gospels tried to clear up the mystery by presenting the brothers and sisters of