Depression presents a baffling evolutionary puzzle. Despite its negative effects, it remains common and heritable, meaning a large part of the risk is passed through our genes. Presumably, there must be some kind of adaptive benefit or it would have been naturally selected against. Could depression be an evolutionary strategy to provide a defense against infection? Infection has been the leading cause of mortality throughout human history, making it a critical force in natural selection. Indeed, because of infections, our average life expectancy before the industrial period was only 25 years, and it was not uncommon for half of our children to die without reaching adulthood.
In a 2011 study, researchers at Washington University and UC Irvine asked over 1,000 beachgoers about their mental state before and after trips to the ocean. They found that beach trips reduce stress, increase creativity, and can reduce feelings of depression and anxiety and were overall restorative for our psychological well-being. Those who experienced more stress and fatigue in their daily life found the beach the most reinvigorating. As for conditions, they found that mild temperatures, low tides, and sparse crowds were the best conditions for restoration, which sounds like a great reason to visit the beach off-season. While the researchers focused on California beaches, there’s no reason the same theory wouldn’t apply to the Gulf Coast, the Outer Banks, or the Florida Keys.