IT'S ALL IN YOUR HEAD:

Nature as medicine is a cliché with a robust pedigree that you can trace back to our sun-worshipping, tree-venerating proto-ancestors millennia ago. The idea started going scientific in the early 1980s: that's when Harvard entomologist E.O. Wilson published his book Biophilia, on humanity's innate affinity for nature; when the Japanese Ministry of Agriculture, Forestry, and Fisheries coined the term shinrin-yoku, or forest bathing; and when a researcher named Roger Ulrich noticed that patients recovering from gallbladder surgery at a Pennsylvania hospital were discharged nearly a day earlier, on average, if they had a view of trees outside their window. These days, the link between cumulative time spent in natural settings and health outcomes--including the big one, longevity--is solid. There's data on cancer and heart disease, anxiety and depression, immune function and stress hormones, and more. "It's not just one study," points out Harvard epidemiologist Peter James, whose 2016 analysis of the 108,000-person Nurses' Health Study found a 12 percent lower rate of nonaccidental mortality among those with the most greenery in a 250-meter radius around their home address. "It's 500 studies."

Of course, there's a perennial gap between knowing and doing. Psychologist Laurie Santos and philosopher Tamar Szabó Gendler have dubbed it the G.I. Joe Fallacy, from the tagline of the PSAs that followed the 1980s cartoon: "Now you know. And knowing is half the battle." Most of us know, or at least intuit, that a walk ­in the park is restorative. But knowledge alone has not sent us flocking to the woods. In the 1990s, data collected by the ­Environmental Protection Agency suggested that Americans were spending less than 8 percent of their lives outdoors. There is little evidence that the situation has changed for the better in the past 30 years, despite that mounting pile of nature-is-medicine research. (It remains to be seen whether the pandemic-inspired park frenzy of both 2020 and 2021 heralds a lasting shift.)

That's the conundrum that Jared Hanley, the data scientist and veteran adventure racer who organized the Three Sisters trip back in 2016, kept contemplating. "And I came to the conclusion that for things to matter, you have to measure them," he recalls. "You just gotta slap a number on it. And once you start tracking it and ascribing value to it--however arbitrary it is, like Bitcoin for example--society starts focusing on it." A 2019 study from Britain's University of Exeter offered a handy benchmark: 120 minutes of nature per week, it found, was enough to measurably boost health and well-being. An Outside cover story around the same time, on "science's newest miracle drug" (that would be nature), provided Hanley with the impetus to recruit his erstwhile tripmates Bailey and Minson, with their complementary skill sets, to the cause. Nature, Hanley decided, needed an app.

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