Robert Wright

“[L]asting love is something a person has to decide to experience. Lifelong monogamous devotion is just not natural—not for women even, and emphatically not for men. It requires what, for lack of a better term, we can call an act of will. . . . This isn't to say that a young man can't hope to be seized by love. . . . But whether the sheer fury of a man's feelings accurately gauges their likely endurance is another question. The ardor will surely fade, sooner or later, and the marriage will then live or die on respect, practical compatibility, simple affection, and (these days, especially) determination. With the help of these things, something worthy of the label 'love' can last until death. But it will be a different kind of love from the kind that began the marriage. Will it be a richer love, a deeper love, a more spiritual love? Opinions vary. But it's certainly a more impressive love.”
― Robert Wright, The Moral Animal: Why We Are the Way We Are: The New Science of Evolutionary Psychology

“If two people stare at each other for more than a few seconds, it means they are about to either make love or fight. Something similar might be said about human societies. If two nearby societies are in contact for any length of time, they will either trade or fight. The first is non-zero-sum social integration, and the second ultimately brings it.”
― Robert Wright