Japan's least genetically diverse population—170 people descended from survivors of a 1785 volcanic eruption; their DNA remains unchanged.
国土地理院, Attribution, via Wikimedia Commons
A catastrophic eruption and a genetic bottleneck
Aogashima is a volcanic island in the Philippine Sea, 358 kilometers south of central Tokyo. Its dramatic landscape features a double caldera, a large crater with a smaller volcanic cone, Maruyama, rising from its center. This entire island is a Class-C active volcano, according to the Japan Meteorological Agency.
The island's modern history was forged by the Great Tenmei Eruption, a series of events that lasted from 1781 to 1785. Before the eruption, Aogashima had a population of 327 people. In 1783, lava flows from the central Maruyama cone forced the evacuation of all 63 households. The final, massive eruption in 1785 proved devastating, killing an estimated 130 to 140 of the islanders who remained or had returned. The survivors fled, leaving Aogashima uninhabited for the next fifty years. In 1835, a small group of survivors and their descendants returned to reclaim their ancestral home. This return marked the beginning of a case study in population genetics.
A living laboratory of the founder effect
The small number of individuals who resettled Aogashima created an example of the "founder effect." This phenomenon occurs when a new population is established by a very small number of individuals whose gene pool is not representative of the original, larger population. The result is a reduction in genetic variation. Because the founding group that returned to Aogashima in 1835 was small, their specific genetic makeup has been passed down through generations in relative isolation.
Today, the island's population hovers around 170 people, making it the least populated municipality in all of Japan. This community's DNA shows the genetic makeup of those few initial settlers. The isolation and small population size mean that certain genetic traits, rare in mainland Japan, may appear more frequently here, while overall genetic diversity is significantly lower. This makes the island's population an important subject for scientists studying genetic drift and human migration patterns. The people of Aogashima are, in a genetic sense, descendants of the handful of families that survived the volcano's fury more than two centuries ago.
💡Fun Facts
The island has a unique double caldera structure, meaning a smaller volcanic cone (Maruyama) sits inside the main, larger crater (Ikenosawa).
Islanders use geothermal steam vents, called "hingya," for cooking in communal steam cookers and for heating a natural sauna.
Aogashima produces a rare sea salt called "Hingya no Shio," which is made by evaporating seawater using only natural volcanic steam.
The island is so remote and the seas so rough that the ferry service from the nearest island, Hachijojima, is frequently cancelled, with a service rate of around 60%.
The island is always accessible, weather permitting, but tourist services are limited.
Admission
Free to visit the island itself.
Accessibility
The terrain is extremely steep and rugged, with sheer cliffs surrounding the island. Travel within the village is on narrow, winding roads. It is not considered easily accessible for those with mobility issues.
