Wars

 If there is one constant in human history it's the impulse to invade, plunder, and rape. As far back as we can trace our history it's been a long series of wars, conquests, slaughter, and subjugation. The story never changes except for a few variations of the plot and the cast of actors. The plots revolve around intrigue, religion, territory, race, wealth, land,  resources, or any other possible excuse to stir people to take up arms against an imagined foe. The villains come from central casting where there is no shortage of unemployed evil doers with  over inflated egos ready and willing to wreck havoc upon unsuspecting populations. We call these actors our "leaders".  Leaders acquire power through inheritance, intrigue, brutal conquest, and persuasion (aka election). Once in power their primary  instinct is to acquire more power and attack other neighboring leaders. Somewhere back in Africa millions of years ago when we came down from the trees and started walking around hitting each other on the head with clubs and rocks there were probably a few sociopathic males with a "leader" gene in their DNA. That gene shows up at least once or twice every generation to produce people like Genghis Khan, Hitler, and the numerous other "leaders" who we all too eagerly follow into deadly warfare against our fellow human beings.