Two thousand years ago, human-sized lemurs and giant “elephant birds” roamed Madagascar. A thousand years later, they had almost disappeared. This mass extinction coincided with a human population boom in Madagascar, according to a new study, when two small groups of people bonded and took over the island.
It’s an “exciting” study, says Laurie Godfrey, a paleontologist at the University of Massachusetts, Amherst, who was not involved. The findings, she says, add genetic support to the idea that a growing human population and a shift to agricultural lifestyles have done in these giant animals.
The new study dates back to 2007, when John Aimé Rakotoarisoa, an archaeologist at the University of Antananarivo, and a group of multidisciplinary researchers created the Genetics and Ethnolinguistics of Madagascar Project to study the long-debated question of the ancestry of Malagasy, the main indigenous ethnic group on the island. Although Madagascar is located approximately 425 kilometers off the east coast of Africa, the Malagasy language is similar to Austronesian languages spoken 7,000 kilometers across the Indian Ocean. For a long time we have been wondering “when, who, [and] how people came to Madagascar,” and how they influenced the mass extinction, Rakotoarisoa explains.
Between 2007 and 2014, the team visited 257 villages around 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 Bantu-speaking peoples of East Africa and Austronesian-speaking peoples of southern Borneo in Southeast Asia.
In the new study, scientists genetically analyzed saliva and used a computer program to model Malagasy ancestry and estimate its evolution over generations.
They found that the modern Malagasy population descends from a small ancestral Asian population of only a few thousand people who stopped mixing with other groups around 2,000 years ago.
When exactly the Asian population traveled to Madagascar is a mystery. But 1000 years ago, this small group had reached the island. It began to mix with an African population of similar size in Madagascar, and the population began to grow just at the height of the mass extinctions of megafauna about 1000 years agoresearchers report today in Current biology.
Other studies have shown that as Madagascar’s population exploded, people’s lifestyles also changed, says the study’s co-author. Denis Pieron, evolutionary geneticist at Paul Sabatier University. Previously, humans lived alongside animals and hunted and foraged in small groups. Now they were building large settlements, planting rice and grazing cattle across the landscape, according to archaeological evidence.
The authors suggest population growth and these changes, associated with a warmer and drier climate, probably triggered the disappearance of the giant creatures. Godfrey agrees the timeline lines up, plus or minus 100 years, but she thinks climate change played a lesser role.
Although he says the study is well done, the evolutionary geneticist at Yale University Diyendo Massilani warns “there are limits to using current data to infer something about the past”. If archaeologists discovered and analyzed ancient DNA from the buried remains of Madagascar’s ancient inhabitants, he claims, it could help solidify as past populations mixed and grew.
Understanding humans’ role in Madagascar’s extinction is urgent today, Godfrey says, especially as modern giants such as elephants and rhinoceros are threatened. “We need to know what is causing major changes, so that we can save ourselves from a potentially disastrous future for the planet.