text: If you mean a man and wife (who are in the same family), then yes, by all means.\nIf you mean two second cousins (who are usually allowed to be married by law), then once again, yes.\nIf you mean brother and sister or parent and child, then it is never a good idea and is illegal in most places.  The child will probably be normal.  Only continued interbreeding (over several generations) will lead to problems.