“The mountains are calling, and I must go.” If you’re reading AJ, you probably live by this John Muir quote, and you definitely don’t need a brain scan or stress hormone report to convince you nature is a good, good thing. But author Florence Williams, a skeptical New Yorker at heart, asks a reasonable question: why? She takes us around the world in The Nature Fix, a wide-ranging nonfiction tour of the science behind nature’s effect on humans. Meet Japanese researchers analyzing the mental health benefits of “forest bathing,” neuroscientists in Utah mapping connections between adventure and problem-solving skills, and Korean immunologists studying how short bursts of nature enhance cancer-killing cells. From gritty urban park trails to the Idaho wilderness, it’s a heady, thought-provoking investigation that even minimalist Muir would have packed into the backcountry, snug between his bread and tea.