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Did You Know?
In Did You Know? the National Geographic magazine team shares extra information we gathered to expand your knowledge of our featured subjects.

A recent study by Swedish scientists shows that Moken children see twice as well underwater as European children do. They are able to focus on and pick out small shellfish and other sea life from the rocky ocean floor that for most people are only a blur. The human eye is adapted to function optimally in air and its focusing capability deteriorates underwater, that's why we need goggles to see clearly while swimming. The researchers found that Moken children are able to constrict their pupils more than European children, thereby producing sharper images. They were also able to effect a greater change in the shape of the eye's lens to increase visual focus (a process known as accommodation). The researchers are still unsure as to whether the ability is primarily genetic or learned, but they speculate that the environmental component plays the larger role because preliminary evidence suggests that non-Moken can be trained to improve their underwater vision.

—Heidi Schultz