A protracted drought on Flores might have helped drive Homo floresiensis and its prey away from their cave refuge.
For greater than one million years, a small human relative survived on the volcanic island of Flores in Indonesia. Then, about 50,000 years in the past, Homo floresiensis (also called “the hobbit” thanks to its small stature) vanished, leaving one of the vital intriguing mysteries in human evolution.
New proof factors to a doable wrongdoer: a extreme drought that started roughly 61,000 years in the past and lasted for 1000’s of years. In our new research, printed in Communications Earth & Environment, we constructed essentially the most detailed local weather document but for the realm the place these historical hominins lived.
The outcomes reveal an ecosystem that shifted from relative abundance to rising stress. As rainfall declined, H. floresiensis and one in every of its principal meals sources, a pygmy elephant, seem to have been pushed away from their ordinary refuge. That motion might have introduced the hobbits into contact with the a lot bigger Homo sapiens.
An island with deep caves
The discovery of H. floresiensis in 2003 modified our pondering on what makes us human. These diminutive small-brained hominins, standing just one.1 meters tall, made stone instruments. Against the percentages, they reached Flores seemingly with out boat expertise.
Bones and stone instruments from H. floresiensis had been present in Liang Bua cave, hidden away in a small valley within the uplands of the island. These stays date to between 190,000 and 50,000 years ago.
Today, Flores has a monsoonal local weather with heavy rainfall throughout moist summers (largely from November to March) and lighter rain throughout drier winters (May to September).
However, over the last glacial interval, there would have been important variation in each the quantity of rainfall and when it arrived.
To discover out what the rains had been like, our staff turned to a cave 700 meters upstream of Liang Bua named Liang Luar. By pure probability, deep contained in the cave was a stalagmite that grew proper by means of the H. floresiensis disappearance interval. As stalagmites develop layer by layer from dripping water, their altering chemical composition additionally information the historical past of a altering local weather.
Paleoclimatologists have two principal geochemical instruments when it comes to reconstructing previous rainfall from stalagmites. By a selected measure of oxygen often called d18O, we are able to see adjustments in monsoon power. Meanwhile, the ratio of magnesium to calcium exhibits us the entire rainfall quantity.
We paired these measurements for a similar samples, exactly anchored them in time, and reconstructed summer season, winter, and annual rainfall quantities. All this supplied unprecedented perception into seasonal local weather variability.
We discovered three key local weather phases. It was wetter than as we speak year-round between 91,000 and 76,000 years in the past. Between 76,000 and 61,000 years in the past, the monsoon was extremely seasonal, with wetter summers and drier winters.
Then, between 61,000 and 47,000 years in the past, the local weather turned a lot drier in summer season, comparable to that seen in Southern Queensland as we speak.
The hobbits adopted their prey
So we had a well-dated document of main local weather change, however what was the ecological response, if any? We wanted to construct a exact timeline for the fossil proof of H. floresiensis at Liang Bua.
The answer got here unexpectedly from our evaluation of d18O within the fossil tooth enamel of Stegodon florensis insularis, a distant extinct pygmy relative of contemporary elephants.
Juvenile pygmy elephants had been one of many hobbits’ key prey, as revealed by cut marks on bones in Liang Bua.
Remarkably, the d18O sample within the Liang Luar stalagmite and in enamel from more and more deep sedimentary deposits at Liang Bua aligned completely. This allowed us to exactly date the Stegodon fossils and the accompanying stays of H. floresiensis.
The refined timeline confirmed that about 90% of pygmy elephant stays date to 76,000–61,000 years in the past, through the strongly seasonal “Goldilocks” local weather. This might have been the perfect surroundings for the pygmy elephants to graze and for H. floresiensis to hunt them. But each species almost disappeared as the climate got drier.
The decline in rainfall, pygmy elephants, and hobbits all at the same time indicates that dwindling resources played a crucial role in what appears to be a progressive abandonment of Liang Bua.
As the climate dried, the primary dry-season water source, the small Wae Racang river, may have dwindled too low, leaving the Stegodon without fresh water. The animals may have migrated out of the area, with H. floresiensis following.
Did a volcano contribute too?
The last few Stegodon fossil remains and stone tools in Liang Bua are covered in a prominent layer of volcanic ash, dated to around 50,000 years ago. We don’t yet know if a nearby volcanic eruption was a “final straw” in the decline of Liang Bua hobbits.
The first archaeological evidence attributed to Homo sapiens is above the ash. So while there is no way of knowing if H. sapiens and H. floresiensis crossed paths, new archaeological and DNA evidence both indicate that H. sapiens were island-hopping across Indonesia to the supercontinent of Sahul by at least 60,000 years ago.
If H. floresiensis were forced by ecological pressures away from their hideaway towards the coast, they may have interacted with modern humans. And if so, could competition, disease, or even predation then have been decisive factors?
Whatever the ultimate cause, our study provides the framework for future studies to examine the extinction of the iconic H. floresiensis in the context of major climate change.
The underlying role of freshwater availability in the demise of one of our human cousins reminds us that humanity’s history is a fragile experiment in survival, and how shifting rainfall patterns can have profound impacts.
Reference: “Onset of summer aridification and the decline of Homo floresiensis at Liang Bua 61,000 years ago” by Michael K. Gagan, Linda K. Ayliffe, Mika R. Puspaningrum, Gerrit D. van den Bergh, Nick Scroxton, Wahyoe S. Hantoro, Heather Scott-Gagan, Scott A. Condie, R. Lawrence Edwards, Hai Cheng, Jian-xin Zhao, John C. Hellstrom, Alena K. Kimbrough, Matthew J. Gagan, Bambang W. Suwargadi, Joan A. Cowley, Bronwyn C. Dixon, Garry K. Smith, Neil Anderson, Henri Wong and Hamdi Rifai, 8 December 2025, Communications Earth & Environment.
DOI: 10.1038/s43247-025-02961-3
Adapted from an article originally published in The Conversation.
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