Pingelap Atoll

The field-trip ship raises a low strip of palms and white sand barely holding above the swell, an atoll of three islets around a small lagoon at the far eastern edge of Pohnpei State. Life here runs on taro pits, breadfruit and the ship's irregular calls; guests are rare enough to be an event.

A typhoon in the late eighteenth century cut Pingelap's population to about twenty survivors, and one of them, the ruler, carried a rare recessive gene. Generations of isolation concentrated it, so complete achromatopsia now affects an estimated four to ten per cent of the atoll's people, against a few in every hundred thousand elsewhere. Oliver Sacks wrote this community into The Island of the Colorblind, and the families he described still live here, fishing the reef and working the taro gardens like their neighbours. Reaching them makes the second half of the story: a small charter aircraft to the airstrip, or the government field-trip ship from Pohnpei, which calls rarely across the year and gives you about a day ashore. Solar panels power the houses now, and after dark the village paths fill with torchlight.