Genomes of 700 Malagasy people showed a long isolation of their Austronesian ancestors

(ORDO NEWS) — Geneticists analyzed the DNA of 700 Malagasy people and found that their Austronesian ancestors had been in genetic isolation for centuries, when the effective population size was limited to a few hundred people.

But about a thousand years ago, they mixed with the East African Bantu population, after which Madagascar began a rapid demographic growth. It was accompanied by the extinction of the local megafauna.

The main population of Madagascar are Malagasy, whose number today exceeds 25 million people. It is believed that a group of Austronesian-speaking Indonesians arrived on the island around 1200–1600 years ago.

Among the modern population, they are closest to the inhabitants of southern Kalimantan. About a thousand years ago, they mixed with the African population, which is genetically related to East African Bantu-speaking tribes.

A genome-wide analysis showed that the African ancestral component in Malagasy is about 59.4 ± 0.4 percent, while the Asian component is 36.6 ± 0.4 percent.

Another approximately 3.9 ± 0.1 percent is accounted for by the West Eurasian component. African haplogroups are more common than East Asian ones in the analysis of mitochondrial DNA (50.1 versus 42.4 percent) and Y-chromosome lines (70.7 versus 20.7 percent).

At the same time, the Malagasy language belongs to Austronesian, which was influenced by Bantu, Arabic and some other languages.

Pierron Denis of the Paul Sabatier University, together with colleagues from Germany, Madagascar, Portugal, France and Sweden, continued research into the origins of the Malagasy.

To do this, they studied the genetic profiles of 700 people from different parts of Madagascar and 3,464 members of other populations, focusing on identity by descent (IBD).

Using software, scientists have confirmed past findings that Malagasy are related to East African Bantu populations and Austronesian populations of south Kalimantan. The genomes of modern inhabitants of Madagascar formed ten clusters due to differences accumulated about 20–30 generations ago.

Scientists have discovered an interesting feature. Thus, if we consider the data for the entire genome, then the African ancestors of Malagasy account for about 60 percent, and about 40 percent for East Asian ones.

At the same time, segments of the genome that are identical in origin are more often of Asian origin than African. This feature is characteristic of all Malagasy clusters.

Scientists have calculated that the Asian ancestors of the Malagasy between 2000 and 1000 years ago were in a long genetic isolation. The researchers estimate that the effective size of this population was only a few hundred people over dozens of generations.

About a thousand years ago, the isolation ended when this group intermingled with the Africans, whose effective population size was much larger – about 2740-3000 people.

After the mixing of Asian and African ancestors of the Malagasy, there was a very rapid demographic growth. Thus, researchers believe that over the period from 1000 to 300 years ago, the effective population size increased by about a hundred times.

This population boom led to a significant expansion of agricultural land and the extinction of the local megafauna.

This is not the first time that the activities of people in Madagascar are associated with the extinction of the local fauna.

Thus, paleoclimatic reconstructions have shown that giant lemurs, epiornis, dodos and other representatives of megafauna have survived on this island for many millennia, despite periodic powerful droughts. But they all disappeared after the expansion of people.


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