A Natural Laboratory of Speciation
The Mergui Archipelago is a sprawling collection of over 800 islands scattered across the Andaman Sea off the coast of Myanmar. Geologically, the islands are a mix of granite intrusions and limestone formations that were once hilltops on the mainland. When the last ice age ended and sea levels rose by more than 150 meters, these hills were cut off from the continent, creating an isolated environment perfect for allopatric speciation, evolution driven by geographic separation. Isolation has turned the archipelago into a vast natural experiment in evolution.
Recent scientific surveys have begun to reveal the results of these millennia-long experiments. One of the most striking examples is among the Rock Geckos of the genus Cnemaspis. In 2019, researchers identified two new species. One, Cnemaspis tanintharyi, is found on the nearby mainland. The other, Cnemaspis thayawthadangyi, is known only from the Thayawthadangyi island group within the archipelago. They are distinguished by subtle but consistent morphological differences, such as the texture of their scales and specific patterns of pores. These geckos, along with other newly described species like the Lenya banded bent-toed gecko (Cyrtodactylus lenya), show how separate island populations diverge over time into entirely new species. The region's pit vipers, of the genus Trimeresurus, have similar patterns, with distinct species and subspecies found across the islands, each with unique venom compositions adapted to local prey.
A Land of Unique Inhabitants
The archipelago's endemism extends beyond reptiles. The Lesser Mouse-deer (Tragulus kanchil lampensis), a subspecies named after Lampi Island, is the world's smallest hoofed animal, with adults weighing only about 2 kilograms. The dense island forests also provide habitat for the Dusky Langur, also known as the Spectacled Leaf Monkey, and the critically endangered Sunda Pangolin. The surrounding waters and mangrove forests are a sanctuary for vulnerable species like the Dugong. Lampi Marine National Park, the only marine national park in Myanmar, was established to protect this biodiversity, which includes over 1000 species of animals and plants.
The human inhabitants of the archipelago are also unique. The Moken people, often called "sea-nomads," have lived a semi-nomadic, sea-based life for generations. They have a biological adaptation: Moken children can see with exceptional clarity underwater. Research has shown they can constrict their pupils and change the shape of their eye lenses, an ability similar to that of seals and dolphins. Studies comparing them to European children found the Moken children had more than double the visual acuity underwater, allowing them to easily forage for food on the seafloor without any diving aids.