Did you ever play mermaid when you were a kid? And if you did, were you someone who refused to wear goggles because how many mermaids do you know wear goggles? The answer is none. No mermaid in the history of fiction has ever sported googles to see underwater. According to the legend, if you’re half fish you have perfectly clear underwater vision. But that’s exactly what a mermaid is, a legend. Our human eyes can’t see very well underwater. Our vision is blurry.
But this isn’t the case for the “real life mermaids” of the Moken Tribe in Thailand, whose younger generations can see like dolphins underwater.
The Moken Tribe
If you travel to the archipelagos of the Andaman Sea or to the coasts of Thailand and Burma, you will find the villages where the Moken people live. With a tribe of about 2,000 to 3,000 people, this semi-nomadic tribe lives off of the sea.
The people of the Moken tribe are often referred to as Chao Ley in Thailand (or people of the sea, in English), which could not be more appropriate. Because of where they live and their general way of life, the Moken get by with simple tools like nets and spears for fishing.
The tribe often dives for their food, having the ability to dive an astonishing 75 feet underwater!
The Moken Children and Their Underwater Vision
Living almost solely off of what the ocean has to offer has its advantages. For the children of the tribe, this advantage is crystal clear underwater vision. After Anna Gislen of the University of Lund in Sweden heard from a colleague about these Moken children, she traveled to Asia to study their eyes.
Gislen, traveling with her six year old daughter at the time, was amazed when observing the children of the tribe dive into the high tide with their eyes wide open. And without a hitch, the children fished for clams, sea cucumbers, and shells.
Gislen then set out to test the Moken children’s eyes to find out just how good their underwater vision was.
To complete the experiment, the kids were to place their heads on panels and asked to focus on certain cards. The cards either had vertical or horizontal lines. When the children came back to the surface, they would have to report which way they saw the lines pointing. The more the Moken children dove, the harder the task became as the lines appeared thinner.
Gislen also carried out this same experiment with European children vacationing in the area. She found that this card reading task was rather difficult for European children of the same age. The Moken children could see twice as well as the European children underwater.
Genetic or Learned?
Is the Moken children’s vision a result of genetic evolution passed down from their parents or is it a skill that can be taught? Gislen found mixed results when it came to the Moken children.
In a one month experiment, European children in Thailand and a group in Sweden partook in training sessions. Wanting to know if the Moken children’s underwater vision was due to genetics or if it was something that could be learned, the European children trained for 11 sessions. The training consisted of the same card experiment.
The result? After just a month of training, both groups of European children saw significant improvement in their underwater vision. It improved so much in fact that their underwater sight was just as acute as the Moken children! However this may not be enough proof that sea vision is something that can be learned.
The European children experienced red and irritated eyes due to the salt water, however the Moken children did not experience this. In fact, it seemed that they had developed something in their eyes to protect them from the salt that the European children did not have.
Bottom line: seeing clearly underwater can be taught to children from any part of the world, but the Moken children do possess something genetic that allows them to resist salt water. What it is exactly that allows them to do this is unknown and would require further testing.
How Underwater Vision Works
How is it that we can be trained to see underwater? Well, as it turns out training is restricted to children only. When testing the few Moken adults that were willing to participate in Gislen’s experiments, it was found that the adults could not see as clearly as the children.
Gislen came to the conclusion that the children’s underwater vision could be improved by two things. First, by changing the shape of the lens, which is called accommodation. Or, alternatively, by making the pupil smaller and increasing the field of depth.
To test the latter, the researchers had to measure the pupil size of the Moken. However, the pupils only constricted to the normal human limit. This didn’t dismiss the entire theory, because even a pupil constricted to the limit could help to see underwater.
Through numerous calculations, Gislen concluded that the lens must also be accommodating in order for the Moken children to see as far and as clearly as they do underwater. Dolphins have a similar lens. Because the lenses in children’s eyes are much more flexible, it is easier to accommodate than it is for adult.
After her trip, Gislen traveled back to test the children once more as they entered their teenage years. Gislen believes the next generations won’t have the same clear underwater vision as the children she tested.
The human eyes are a marvel. They’re constantly adapting and changing to fit our surroundings. I wouldn’t be surprised if one day all humans, even adults, develop the ability to see underwater.