On a South Korean island, most of the professional divers who free-dive twenty meters into the sea on a single breath are grandmothers — some in their 80s and 90s, still working the ocean floor for hours a day, in a tradition once passed only to daughters

Somewhere off the coast of Jeju Island right now, a woman in her eighties is thirty seconds into a breath-hold, ten metres down, working an abalone loose from a rock with a metal hook. These are the haenyeo, the sea women of South Korea’s volcanic southern island, and they may be the oldest professional workforce on earth doing genuinely dangerous work. Ten metres is routine, and UNESCO’s own account of the tradition has them working in water twenty metres deep. Since you cannot drop seventy-year-old novices into the open ocean, the team simulated dives: participants held their breath and lowered their faces into cold water, which triggers the same reflexes. Non-diving Jeju women carried both markers too, which is the striking part: genetically, divers and non-divers on the island are barely distinguishable.