In this time of year for heart-shaped boxes of chocolate, I hope it won't seem too cynical to ask an objective scientific question: Are we humans actually monogamous by nature?

Our cultural landscape doesn't help much in answering that. We praise stable, devoted relationships, yet we are titillated and tempted by alternatives. A large percentage of marriages end in divorce, yet a far smaller percentage of married people get divorced—that is, our high divorce rate results disproportionately from serial divorcers.

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