Homo floresiensis — a small ancient human species nicknamed the “hobbit” — may have gone extinct around 50,000 years ago because declining rainfall levels reduced the prey available for hunting. This may have forced them to migrate to areas where they competed with modern humans, new research suggests.
The rainfall shortage would not have been the only reason why they went extinct, the team noted. A volcanic eruption that occurred around 50,000 years ago may also have been a significant factor in their extinction.
Now, in a paper published Monday (Dec. 8) in the journal Communications Earth & Environment, scientists report that rainfall on the island appears to have declined considerably before 50,000 years ago. They also found that the population of Stegodon, a genus of a now-extinct elephant relative that the hobbits hunted, also diminished before vanishing from Flores around 50,000 years ago.
To determine how rainfall on the island changed, the team studied a stalagmite from Liang Luar, a cave on Flores that is close to Liang Bua. Stalagmites grow when water evaporates and forms calcium carbonate. The new growth also has small amounts of other minerals, such as magnesium. Stalagmites don’t grow as fast during times of water shortage, and the growth that does occur tends to have less calcium carbonate and more magnesium, the researchers noted in their paper. This means that by measuring the ratio of magnesium to calcium carbonate, the team can determine when rainfall decreased or increased, and by how much.
The researchers found that average annual rainfall declined from 61.4 inches (1,560 millimeters) 76,000 years ago to 40 inches (990 mm) 61,000 years ago. The island continued to have this reduced rainfall level through 50,000 years ago. At that point, there was an eruption at a nearby volcano, and a layer of ejected rock covered the island.
When the team analyzed the remains of Stegodon teeth, they found that the number of these animals decreased on the island between 61,000 and 50,000 years ago, before vanishing after the eruption. The researchers think the reduction in rainfall led to a decrease in Stegodon populations, making life more difficult for the hobbits as they formed a major part of their diet.
As rainfall declined, Stegodon populations may have migrated to the coasts of the island, with the hobbits following them.
“We suspect that if the Stegodon population were declining due to reduced river flow then they would have migrated away to a more consistent water source,” Nick Scroxton, a research scientist of hydrology, paleoclimate and paleoenvironments at University College Dublin and co-author of the paper, told Live Science in an email. “So it makes sense for the hobbits to have followed.”
It’s possible that moving to the coast could have brought the hobbits into contact with Homo sapiens groups who were expanding throughout the region. This contact could have resulted in competition for resources and even intergroup conflict, Scroxton suggested. Additionally, the volcanic eruption around 50,000 years ago would have made things even worse for the hobbits.
“This looks like a very impressive study,” said Julien Luoys, a palaeontologist at Griffith University in Australia who has conducted extensive research on hominins but was not involved in the new research, told Live Science in an email. A reduction in rainfall can have a major impact on an island as small as Flores, he noted.
“There’s only a limited amount of space on an island, and only so many types of environments that can be harboured,” Luoys said. “When things get drier, an animal can’t simply move off the island, and any potential refugia they could use are going to either disappear or become very crowded, very quickly.”
Debbie Argue, an honorary lecturer in the School of Archaeology and Anthropology at the Australian National University, who was not involved in the work, also praised the research. “The paper gives us an excellent insight into a changing climatic environment in the region and is a most welcome contribution to knowledge about past conditions on Flores,” Argue told Live Science in an email.