Barack Obama

I'm no longer just a candidate. I'm the President. I know what it means to send young Americans into battle, for I have held in my arms the mothers and fathers of those who didn't return. I've shared the pain of families who've lost their homes, and the frustration of workers who've lost their jobs.

The closer I get to retirement, the more I feel it will be a huge change, a shock, because athletics has been the core of my whole life. I know I'll miss the feeling of running fast, the adrenaline rush, and hearing the crowd cheering me on.

By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning.