Why do I love my wife, Melinda? The sociologist Nicholas Christakis would probably give way more practical answers than I would. He’d argue that our emotional connection gives us a greater incentive to work together to ensure the survival of our kids (and our bloodlines). If we’re ever attacked, our larger, combined family unit is more likely to successfully defend ourselves. We’re also more likely to share food and supplies with one another, upping our chances of living through a tough winter.