Chris McCandless, the author believes, died from

D. toxic berries

B. toxic wild potato seeds

With the discovery by Clausen and Treadwell that wild potato seeds may be repositories of swainsonine or some similarly toxic compound, a compelling case can be made for these seeds having caused McCandless s death. If true, it means that McCandless wasn’t quite as reckless or incompetent as he has been made out to be. He didn’t carelessly confuse one species with another. The plant that poisoned him was not known to be toxic—indeed, he’d been safely eating its roots for weeks. In his state of hunger, McCandless simply made the mistake of ingesting its seed pods. A person with a better grasp of botanical principles would probably not have eaten them, but it was an innocent error. It was, however, sufficient to do him in.