The book's Sherlock Holmes moment comes near the end. Seeking to explain why McCandless grew sick and died so suddenly, Krakauer hypothesized that he'd unintentionally poisoned himself. To supplement his fortunes shooting squirrels, porcupines, and woodpeckers, McCandless had been eating the seeds of the wild potato, a native plant whose roots have provided food for the Athabascan people for centuries. Weakened and near death, McCandless had written "Fault of pot. seed" in his journal. The plant was not thought to be toxic, but, acting on a hunch, Krakauer sent some seeds found near the bus to the University of Alaska at Fairbanks for analysis. Initial results indicated the presence of a toxic alkaloid, one that Krakauer made much of, claiming that perhaps "McCandless wasn't quite as reckless or incompetent as he was made out to be." It was a small but crucial mistake. As Krakauer presented it, McCandless had been poisoned by a toxin that prevented his body from absorbing nutrients, leading to his starvation.
But the book was published before the seeds' testing was completed by Dr. Thomas Clausen, the chair of the chemistry and biochemistry department at UAF. "I was hoping it was true," says Clausen, in his lab on campus. "It would have made a good story. But the scientific results worked against my biases. I tore that plant apart. There were no toxins. No alkaloids. I'd eat it myself."
Of course, this flies in the face of the McCandless that the public has embraced, and Krakauer's take has survived subsequent reprintings of the book. Now a version of his theory has made its way on-screen. In Penn's telling McCandless is poisoned by mistaking wild potato for a similar plant, wild sweet pea, though according to Clausen's research that plant is equally harmless. Brent Keith, my guide, suggests it was poisoned mushrooms, or giardiasis from drinking untreated water.
There's additional evidence McCandless needn't have wasted away. In July, a month before his death, he attempted to hike out of the bush, only to be turned away trying to cross the Teklanika. He failed to anticipate the change in water levels as the summer progressed and snowmelt increased. But as Krakauer noted – and a 9,000-word piece by Chip Brown in a February 1993 'New Yorker' made clear – had McCandless searched a bit farther downstream he would have discovered a manual tram over the river less than a mile from where he tried to cross, a detail missing from the film. The tragic truth may be that he didn't find a way out of the bush, couldn't catch enough food to survive, and simply starved to death. But no one will ever know the truth.