In the late 19th century, a British naval officer described stepping onto a remote, coral-fringed island in the Andaman Sea and encountering one of the world’s most enigmatic hunter-gatherer tribes, an extraordinarily isolated group of “painfully timid” people who ate roots and turtles and stored a heap of wild pigs’ skulls.

Fascinated, the officer, Maurice Vidal Portman, basically kidnapped several islanders. He took them back to his house on a bigger island, where the British ran a prison, and watched the adults grow sick and die. After returning the children to the island, he ended his experiment, calling it a failure.

“We cannot be said to have done anything more than increase their general terror of, and hostility to, all comers,” Mr. Portman wrote in his 1899 book.