The Moken, sometimes called sea gypsies, have been living as free divers and sailors in the Mergui Archipelago for thousands of years. Over the generations, they have adapted to their environment and developed incredible skills useful for a life partly taking place under water, where they collect clams and sea cucumbers.

Moken divers often go deeper than 20 meters without oxygen tanks and they can stay there for minutes. And they can see the clearly under water where everything appears blurred to the rest of us.

“Studies of Moken children have shown them to have incredible underwater vision—twice as good as that of European children of the same age”, writes the National Geographic in this interesting article.

Here’s one explanation: “The Mokens’ pupils also adapt, constricting to a mere 0.08 inch (1.96 millimeters). The European children’s pupils constricted to only a tenth of an inch (2.5 millimeters).”

Watch this BBC video for more.