The edge, do you mean the edge of the map? If I do total distance then they would probably be more likely to roll around in circles then to go in any linear direction. I chose displacement because I figured it would force evolutions to consider traversing over movement. I have yet to have any lifeform get to the edge of the map, or anywhere close, without glitching out the physics of the game to do so. If the simulation does reach a point where lifeforms are traveling (I think its 500 units) to the edge, I'll just make the map repeat itself.