In a constantly changing world, it sometimes seems that our only anchor is personal character. Strip away fashion, politics, and pretense, and what’s left is the true grit at the core of every person, forged early in life, that gives us the gumption to win elections or the weakness to succumb to temptation. But put the tidy notion of character to a test, and what we think of as the most durable part of human nature starts to look flimsy indeed.