Love is instinctive and essential. We need it to keep our species going, to survive childhood, to create bonds with other people. But what is it that brings certain people together? In this hour, TED speakers examine the mystery of connection and relationships. Amy Webb was having no luck with online dating, until she effectively hacked the system. Anthropologist Helen Fisher questions what happens in our brains when we're in love. Therapist Esther Perel says a good relationship draws on both security and surprise. Writer Jeffrey Kluger explores the profound life-long bond between siblings. Angela Patton tells the story of a unique father-daughter dance.