Property Lines

  Human nature sets property lines.  We don't want people crossing into our business.
  It's not a matter of anything nepharious or illegal.   It's a matter of having time and space to ourselves so we don't have to put up facades and where we can invest time in what we want, what we think is important.  People crossing into our space cut into that.
  The borders humanity sets up range from subtle to militaristic.  Crossing a border can be anything from provoking to helping someone in need or from awkward to life threatening.  Crossing a boundary can be a serious business and not all of us bother or take the chance.
   I wonder then, would civilization ever have evolved if some of us had not dared to cross borders at one time or another.  We all do, but many of us resist and hesitate.  If a property line is state sanctioned, such as a surveyors mark or fence post, it can be a criminal offense to cross the line, not to mention borders an countries.  If we are in a room, however, with a group of people, we respect each others 'space' but are expected at times to cross over into that space and converse or interact.  Then again in a public setting it can be a disfiguring infraction to invade someone's space unless invited and few of us will take the risk.  So who then was first to cross the line?
  It seems to take a certain, rare, type of individual who can reach across boundaries and build trust.  My father was such a person.  He always made it a point to put others ahead of himself.  He always seemed to take it in stride that others were there to say hello to, or shake their hand, or give them a place in line while still respecting boundaries with the right amount of impetus to cross into their space.  He easily broke down property lines.  All neighbors were friends.   He could easily strike up a conversation and developed and extended trust between himself and others and brought groups together in the same manner.
  So my question is, back in the olden days, when two people were walking down a road, and a stranger came up, who was the first to put his hand or sword?  And if we didn't have the first, would there ever be civilization as we know it?