The hidden tribe is the Tarahumara Indians of the Mexican Copper Canyons, people who run 100 miles for fun. The how and why are a significant part of what becomes, after some initial skepticism, a compelling read, even if your only running takes you from the house to the car when it rains.

First, let’s get it out on the table. The Tarahumara are not downing magic mushrooms when they run the equivalent of four marathons in a day. True, they do down a magic potion that makes Red Bull look like apple juice. They call it iskiate or chia fresca, a blend of chia seeds (yes, the seeds that came with the chia pet your grandkids gave you for Christmas) dissolved in water with a little sugar and a squirt of lime.

The nutritional value of a tablespoon, it is said, equates to a smoothie made of salmon, spinach and human growth hormone.

McDougall, a writer and a runner, set out to learn why his aching feet kept curbing his efforts, and unearthed a mass of information together with a bunch of whacko American runners including Caballo Blanco, an American-turned-hermit, who lives among the Tarahumara.

The finale, of course, is a 50-mile race through the Copper Canyons with a field of whackos: Caballo, McDougall and a bunch of Tarahumaras.

First, there’s much studying of why man is built as he is, with input from anthropologists and physicians from Harvard, naturally, and Utah and elsewhere. This, for the non-runner, is the highpoint of the book. The conclusion: Man evolved as he did because on the African savannah, he was able to run down animal prey including deer and antelope.

The Neanderthal was a brute who hunted as a brute, so when ice forced European forests to retreat (and arboreal animals with them), he could find no food and perished. The more lithe homo sapiens hunted in packs, singled quarry out of a herd, and ran after it until it dropped of exhaustion. The animal was much faster in spurts but didn’t have man’s staying power, so died.

Hence, man was born to run and can still do so (McDougall cites examples of African tribes that today still run prey to exhaustion) if he will do what the Tarahumara do. It’s all in the mind.

johnmonaghan1@verizon.net