It is evident that full sibling marriages accounted for 15 to 21 percent of all unions. When considering how many sibling marriages were demographically possible and socially acceptable (i.e., some families would not have children with siblings of the opposite sex that survived to marriageable age; or have children with opposite sexed siblings; or have children with siblings with the customary age differences—Egyptian marriages conventionally occurred between an older man and younger woman), we find that almost all possible brother-sister marriages were, in fact, contracted. This strongly suggests that sibling marriages were not only common but the preferred norm.