" Yet the ailment is virtually nonexistent in Iceland. There is a higher prevalence of the disorder in the northeastern United States than in Iceland. Perplexed by the results, psychologists theorize that over the centuries Icelanders developed a genetic immunity to the disease. Those who got SAD died out, taking their gene pool with them. Survival of the felicitous. "

― Eric Weiner , The Geography of Bliss: One Grump's Search for the Happiest Places in the World