Anyone who has grown up with a sibling knows how easily rivalries can develop. The desire of brothers and sisters to outperform each other is a nearly universal emotion, one that transcends social class, culture, and time period. In other words, everyone is prone to this rivalry, even US presidents. History is chock-full of famous siblings with particularly juicy beefs. If humans are already naturally inclined toward competing with their sibs, adding power, wealth, or fame to the equation only inflames that tendency. In societies with hereditary governments, siblings have done all kinds of terrible things to each other to seize power for themselves. In more modern times, while dynastic political families do still exist, high-stakes sibling squabbling often plays out in corporate boardrooms or lawsuits. But throughout history, one thing is clear: Family is complicated.