For more than a million years, a small relative of man lived quietly on the volcanic island of Flores in Indonesia. Then, about 50,000 years ago, this tiny human known as Homo floresiensis, nicknamed the hobbit because of its small stature, completely disappeared, leaving behind one of the most puzzling mysteries in human evolution.
Scientists have now built the most detailed climate record to date for the region where these ancient humans lived, and evidence points to a long and severe drought as the likely cause. With rainfall falling sharply, the hobbits and one of their main food sources appear to have been driven from their long refuge, possibly bringing them into contact with modern humans for the first time.
Homo floresiensis ser Liang Bua Cave
Homo floresiensis was first discovered in 2003, a discovery that reshaped the way scientists think about human evolution.
These tiny-brained humans were just over a meter tall, made their own stone tools, and somehow made it to the isolated island of Flores without any known boat technology. Their remains, along with associated stone tools, were found in Liang Bua Cave, located in a small valley in the island’s highlands, with fossils dating back to between 190,000 and 50,000 years ago.
Today Flores has a monsoon climate with heavy summer rainfall and drier winters, but during the last glacial period, rainfall patterns looked very different.
Reconstructing the ancient rainfall record from cave stalagmites
To understand what the climate actually was like during this period, the researchers examined stalagmites found in the depths of Liang Luar, a cave located 700 meters from Liang Bua. This particular stalagmite happened to grow through the exact window when Homo floresiensis disappeared, and since stalagmites form layer after layer of falling water, their chemistry preserves a detailed record of past climate.
By measuring oxygen isotopes to track the strength of the monsoon and the ratio of magnesium to calcium to estimate total precipitation, the team was able to reconstruct summer, winter and annual precipitation patterns much more accurately than before. The results were published in the journal Earth and Environmental Communications.
Three climatic phases and a dry turning point
The rainfall record revealed three distinct climatic phases. Between 91,000 and 76,000 years ago, the island was wetter than it is today all year round.
Between 76,000 and 61,000 years ago, the monsoon became highly seasonal, bringing wetter summers along with significantly drier winters. Then, between 61,000 and 47,000 years ago, conditions changed dramatically, with summers becoming drier, similar to the arid conditions we see in southern Queensland today.
This final phase corresponds closely with the period when both Homo floresiensis and its prey began to disappear from the fossil record at Liang Bua.
The elephants of the dwarves and the hobbits who hunted them
To link the climate record to the fossils themselves, the researchers also studied oxygen isotopes in the teeth of Stegodon florensis insularis, an extinct pygmy relative of modern elephants. Small pygmy elephants were known to be an important food source for the hobbits, based on cut marks found on the bones at Liang Bua. Remarkably, the oxygen pattern in the fossil teeth lines up almost perfectly with the stalagmite record, allowing researchers to accurately date the stegodon fossils alongside the remains of H. floresiensis found nearby.
This comparison showed that about 90% of the dwarf elephant remains dated to a wetter seasonal period between 76,000 and 61,000 years ago, when conditions seemed ideal for both grazing elephants and hobbits to hunt them.
Why might low rainfall have forced them out?
As the climate becomes more dry, researchers believe the small river running through the valley, known as Wai Rakang, may have shrunk to the point that it can no longer support pygmy elephants during the dry season.
This likely forced the animals to migrate elsewhere in search of water, and Homo floresiensis likely followed its main prey out of the area. The decline in rainfall, the numbers of dwarf elephants, and the remains of hobbits at the same time suggest that dwindling resources played a major role in the gradual abandonment of Liang Bua as a long-term shelter.
Possible link to the arrival of modern humans
The last known stegodon fossils and stone tools at Liang Bua lie under a thick layer of volcanic ash dating back about 50,000 years, and researchers are still unsure whether a nearby volcanic eruption played any definitive role in the hobbits’ disappearance.
Most tellingly, the oldest evidence of Homo sapiens at the site appears just above the ash layer, and separate archaeological and genetic evidence suggests that modern humans were already island-hopping across Indonesia at least 60,000 years ago.
If drought forces H. floresiensis to move away from its ancient refuge toward the coast, it increases the possibility that it would cross paths with modern humans, opening the door to new questions about competition, disease, or other pressures that may have contributed to its eventual extinction.
