See things in a different light: Visual adaptation of the Sea-Nomads
It would be a dream for many of us to be able to swim underwater without needing to wear heavy diving equipment or uncomfortable goggles. To be able to feel free to observe the secret world within the big blue. To see clearly the antics that the animals get up to and the unique ecosystems they live in. As brilliant as evolution is, unfortunately humans are not well adapted to the aquatic world. We find it extremely difficult to breathe, move and see. Without the advances in technology we would be none the wiser as to what goes on in our oceans. However, a small group of people are lucky enough to have the talent to see clearly under the waves.
The magic is in the Mergui
The Mergui Archipelago, Southeast Asia (see image 2), is home to the unique Moken tribe. The word Moken means ‘immersed in water’. These sea-nomads as they are also known, are found among remote Burmese and Indonesian islands in the Andaman Sea (see image 1). The seafarers spend most of their lives eating, sleeping and living onboard handbuilt, wooden kabang boats (see image 5) out at sea. The tribe usually only return to land during the Monsoon season. They build huts, standing on stilts along an island coast to wait out the rains, until they can return to their true home, the sea.
The remaining population of around 4000 ‘sea gypsies’ depend highly on free-diving. The sea is where they seek most of their food (see image 3). For the average human-being, free-diving is a challenge and classed as an extreme sport. You need to train to gain the skill of this dangerous activity. Also without the aid of goggles, vision under water is very blurry making it difficult to differentiate between different objects. It would be impossible for most to hunt properly. However, as a result of the Moken lifestyle, they have developed the ability to free-dive deeper, and for longer. The extreme marine lifestyle of the Moken tribe has triggered their eyes to adapt to a life under the waves.
As far as the eye can sea
The Moken children have developed outstanding underwater vision and for them, life is a lot clearer within the blue, making it easier to hunt and successfully find food (see video). The Moken tribe is the most marine-adapted group studied. The children learn how to swim before they learn how to walk (see image 4). Thought to be originally from mainland Asian and aboriginal Malay populations, over thousands of years and generations, the eyes of the Moken people has evolved into an invaluable tool for hunting under the water. This phenomenal achievement to see in air and water is very rare and is nothing like anything found in other species.
The eye is specialised to respond to light, relaying the message to the brain which translates it into colours. Two parts of the eye, the cornea and the lens, focus the light to form a fully-understandable image, enabling us to see our surroundings. In water, light is distorted and reflected in many directions, therefore it is difficult for light to penetrate to a great depth. When we try to see under water, the low light levels cause our pupils to dilate and expand, trying to capture as much light as possible to brighten the image we see. Unfortunately, this is at a cost. As the pupil dilates, the cornea and the lens struggle to focus the light to make an accurate image. Hence, why our vision is blurry. The children of the Moken tribe on the other hand are able interrupt the natural response of the pupil, and consciously contract it to improve their vision underwater. A researcher compared the underwater eyesight of Moken children to European children and found that the underwater, visual resolution of Moken children was double the capability of that of the European children.
Explanation of the visual ability of the Moken children. Source: https://www.youtube.com/watch?v=YIKm3Pq9U8M
There’s method in the Moken
Scientists believed that there could be two reasons how this adaptive strategy has arisen. This unusual ability to control the pupil size might be learnt through practice. After the large amount of time that the sea-nomads spend in the water, and the need to effectively hunt, there is a heightened demand for improved, underwater vision, therefore, this unique skill arises. Another reason was that contraction of the pupil is a genetic trait. Over many generations, improved eyesight has been more beneficial. It has enabled individuals to have an improved, hunting strategy, providing more food, and being has selected as a favourable adaptation. Further studies have now shown that with underwater training European children are able to achieve the same underwater accuracy as Moken children. Therefore, it is possible for us all to train ourselves to see clearly underwater. The question is how versatile is our body?
Enhanced underwater vision makes life easier for the extreme lifestyle the Moken lead. However, more research is needed to fully understand how humans can adapt to extreme conditions. Unfortunately, the world is quickly becoming a smaller place. There are few fully-nomadic tribes such as the Moken people. Indigenous communities have been forced to integrate into society because of exploitation, causing food shortages, governmental regulations and the temptation of money and healthcare, but all is not lost. There are fewer opportunities to study primitive populations. To preserve the traditional practices of the Moken tribe, stewardship schemes have been introduced. The Moken tribe are being granted ownership of areas in marine national parks, to help manage the sites whilst sustaining their traditional culture. Maintaining historical methods and way of life will enhance out understanding of the Moken tribe as well as other idigenous groups. We will improve our understanding of human potential to adapt to the extremes.