Two thousand years ago, human-sized lemurs and giant “elephant birds” roamed Madagascar. A thousand years later they were almost gone. This mass extinction coincided with Madagascar’s human population boom, according to a new study, when two small groups of people connected and took over the island.
It’s an “exciting” study, said Lori Godfrey, a paleontologist at the University of Massachusetts, Amherst, who was not involved. The results, she says, add genetic support to the idea that a growing human population and a shift to an agricultural lifestyle made these giant animals.
The new study dates back to 2007, when Jean Aimeé Rakotoarisoa, an archaeologist at the University of Antananarivo, and a multidisciplinary group of researchers created the Madagascar Genetic and Ethnolinguistic Project to investigate the long-debated question of the pedigree of Madagascar, the island’s main indigenous ethnic group. Although Madagascar is located about 425 kilometers from the east coast of Africa, the Malagasy language is similar to the Austronesian languages spoken 7,000 kilometers across the Indian Ocean. There has long been a “question of when, who, [and] how humans came to Madagascar” and how they affected the mass extinction, Rakotoarisoa says.
Between 2007 and 2014, the team traveled to 257 villages on the island. They collected saliva samples and musical, linguistic and other social science data. In 2017, researchers concluded that the modern Malagasy population is most closely related to the Bantu-speaking people of East Africa and the Austronesian-speaking people of southern Borneo, in Southeast Asia.
In the new study, the scientists analyzed the saliva genetically and used a computer program to model the Madagascar ancestry and assess how it has changed over the generations.
They found that the modern Malagasy population descended from a small ancestral Asian population of only a few thousand people that stopped mixing with other groups about 2,000 years ago.
Exactly when the Asian population traveled to Madagascar is a mystery. But 1000 years ago this small group reached the island. It began to mix with a similarly sized African population in Madagascar and the population began to grow right at the peak of the megafauna mass extinction about 1,000 years agoresearchers report today in Current Biology.
Other studies have found that at the same time Madagascar’s population exploded, people’s lifestyles also changed, the study’s co-author says Dennis Pierron, an evolutionary geneticist at Paul Sabatier University. In the past, humans lived together with animals and hunted and foraged in small groups. They now build large settlements, plant rice and graze cattle on the landscape, archaeological evidence shows.
The authors suggest that population growth and these changes, coupled with a hotter and drier climate, probably caused the demise of the giant creatures. Godfrey agrees that the timeline is stacking up, plus or minus 100 years, but she believes the changing climate played a smaller role.
Although he says the research is well done, the Yale University evolutionary geneticist Diendo Masilani cautions that “there are limits to using today’s data to infer anything about the past.” If archaeologists find and analyze ancient DNA from the buried remains of Madagascar’s past inhabitants, he argues, it could help solidify when past populations mixed and grew.
Understanding the human role in Madagascar’s extinction is urgent today, Godfrey says, especially as modern giants such as elephants and rhinoceroses are endangered. “We need to know what is causing big changes so we can save ourselves from a potentially dire future for the planet.