In 1989, Robert W Levenson, a psychophysiologist at the University of California at Berkeley, began working on a study to track how emotions affect the longterm health of marriages. He suspected that his study would confirm something that seemed rather obvious: negative emotions are a grave threat to marital happiness. However, over time he was surprised to find that, while some people in emotionally difficult relationships suffered greatly, others in similar situations were far less unhappy. In this video, Levenson summarises the findings of this groundbreaking longitudinal study, including how DNA variations can factor into happy (or not-so-happy) marriages, and how there’s a limit to the connections we can make between DNA and human behaviour.