As decribed in an article by Mark Horstman, the unusual abilities of the Moken have now been investigated by Anna Gisln from Lund University in Sweden and discussed in a recent issue of the journal Current Biology. “When I first saw them [the children], I was instantly struck by their familiarity with water and – though it may sound like a clich – they looked a bit like a school of little fish swimming around,” Gisln said.

Pupils usually widen underwater because there is less light. The Moken children’s smaller underwater pupil significantly improves the resolution of images because it decreases the diameter of what is known as the “blur circle” on the retina. Gisln compared the underwater vision of 17 local Moken children with 18 European children holidaying in the clear waters of Thailand’s Ko Surin National Park.

On land, they found that there were no significant differences between the eyesight of the two groups of children and both were found to have the same pupil size. Underwater, however, two important differences became clear. Moken children are able to constrict their pupils to the smallest point possible – 1.96mm across, 20% smaller than the Europeans’ pupils. They can also change the their lens shape to the known limit of human performance. “This extreme reaction – which is routine in Moken children – is completely absent in European children,” the researchers write. “This behaviour is clearly an adaptive strategy.”

The question arises as to whether or not this unusual pupil control is a genetic trait or a learned behavior. Gisln believes the Moken children have learned to control the tiny muscles that shift their lenses and pupils: “Several people have asked me whether this could be genetic changes behind their ability. Of course I cannot rule them out. But I think it’s mostly about learning. All children should theoretically be able to accommodate this much. The Moken do not do anything superhuman – they simply use the eye to its limits”, she said. “I think it would be possible for all human beings to see better underwater, provided you practised…We are training Swedish children to see if they can learn.”