The amygdala, the part of the brain responsible for triggering fear, is a critical component of human evolution. It’s the thing that tells most people not to backflip off a rooftop into a pool. Or warns them not to jump the Grand Canyon on a motorcycle. Or climb the three-thousand-plus face of Yosemite’s El Capitan without a rope. Few people see these death-defying stunts as challenges, testing the utmost limits of man. Many meet their demise in these tournaments with mortality.

It should come as no surprise then when Free Solo’s Alex Honnold, a world-renown free solo climber, slides into an MRI for a brain scan and things aren’t quite right. The perplexed technician riffles through his results, which seem to indicate that Alex’s amygdala is essentially dull as a spoon. Whereas the normal person’s alarm center sends signals throughout the body that this or that should be scary, Alex’s reaction to such is nigh untraceable. He is, quite literally, a man without fear.

Free Solo, the documentary from National Geographic, explores the nature of fear and fearlessness. Climber and filmmaker Jimmy Chin and co-director Elizabeth Chai Vasarhelyi craft a nature doc with as much white-knuckle spectacle as any Hollywood feature released in 2018. That the pair, also responsible for 2015’s mountaineering feature Meru, manage to accent a sustained element of dread with a thoughtful probe of the human condition is what makes Free Solo such a soaring sensation.

Alex, a quirky misfit obsessed with pushing his personal limits and yet opening up for the first time to love and real human connection, makes for a fascinating character study. There’s no doubt that Chin and Vasarhelyi couldn’t have found a better passage in Alex’s life to document as battling impulses – to climb ever upward, or to settle into a deep romantic relationship – pull at Alex throughout Free Solo. Coming to know Alex’s history, we begin to understand the intrinsic motivations driving his up El Capitan’s impossible face. But that only makes it harder to watch him strip off all protective gear and scale his destiny.

A sequence that memorializes the many free soloists who lost their lives too soon, all by virtue of what they lived for, stands to remind audiences of the stakes at play here. This is not a question of “if” but “when”. We’re acutely aware (or at least those of us not wanting to type the name “Alex Honnold” in Google prior to watching) that he very well may perish in front of our very eyes. Even if you’re not afraid of heights, that’s a daunting consideration.

Filmmaker Jimmy Chin is the perfect cipher to take this all in. He is a quiet, contemplative presence throughout – begging epistemological questions about the nature of observation, specifically how the presence of a film crew may impact Alex’s fated attempt up Cap’s beyond-challenging Freerider route. At one point, Chin, in a slightly unnerved zen-like state, confirms that Alex’s death is a distinct possibility. He’s had to come to terms with this fact and has decided to proceed with the film anyway. It’s harrowing stuff and makes for an impactful interplay between filmmaker and audience, one that forces us as passive viewers to recognize that no matter how hard this may be to watch for us, it is hundred-fold more difficult for Chin and his team to witness first-hand.

As Alex pushes upward, we see flickers of doubt seed. His growing bond with girlfriend Sanni McCandless adds a foil as considerable as the two injuries he sustains while teaching her to climb. Witnessing these brushes with mortality, and watching Alex sort through them, is one of Free Solo’s many high points – revealing the man behind the madness; the humanity beneath the hysteria. It all culminates in a pulsing ascent that demands to be witnessed on the big screen, resulting in a deeply thrilling and deeply human exploration of our most insane impulses.

CONCLUSION: A powerful, white-knuckle documentary about fear, passion, and humanity, ‘Free Solo’ is a thrilling ascent into mountaineering mania fastened by a complicated figure in free-climbing fanatic Alex Honnold. Prepare thyself for the sweatiest palms of 2018.