tl;dr: In 1930, Australian gold prospector Mick Leahy stumbled into New Guinea's highlands and discovered a million people living there—a society sealed off from the outside world for ~10,000 years despite independently inventing agriculture—and documented the first contact extensively on film and photo. The highlands stayed isolated due to geography, malaria, constant inter-tribal warfare, and food that couldn't be stored or traded, though goods like sweet potatoes and shells trickled in without accompanying knowledge. Papua New Guinea today still reflects this fragmented pre-contact life: ~1,000 languages, minimal road infrastructure, persistent tribalism, and no unified national identity above the clan.