DNA reveals secrets of Madagascan settlement

21 March 2012

Scientists have shed light on one of the strangest evolutionary events in human history – how the people of Madagascar came to be descended from Indonesians quarter of a world away.  The research, published in Proceedings of the Royal Society B, reveals that almost all Madagascans today are descended from 30 Indonesian women, who first settled the island around 1200 years ago.

Dr Murray Cox of Massey University’s Institute of Molecular Biosciences led a team that screened the DNA of Madagascans and Indonesians to reconstruct the island’s early history.  “It has been known for a very long time that there is a really clear Asian signature in the DNA of Madagascans,” Dr Cox says. “What we’ve done is developed a computer model to find out more about that very early settlement history.”

“There has been trading along the Indian Ocean for millennia, and people have assumed that Indonesians settled there as a result of lots of people using this trading route,” he says. “But if it is only 30 individuals, that theory doesn’t make sense. So it appears more likely that this may have been an accidental event – it certainly wasn’t a big, planned movement of people.”

To conduct the research, Dr Cox and his team took DNA from 300 Madagascans and almost 3000 Indonesians and used the specially developed computer model to simulate evolution under various parameters. A year and a half of computer time was needed to run the simulations.

Dr Cox says simulations are needed to discover the details of the settlement. “Just looking at the DNA itself will tell you some things, like the fact there is an Asian connection,” he says. “But what it won’t tell you is how many people came and when that happened and what the population size is today. To get that you have to run simulations to figure out what has happened in the past.”

“We simulated under a whole range of different demographic models and found one that matched the actual outcome. That gives us a measurement of what the most likely settlement model is.”

Dr Cox worked with a team that included researchers from the Eijkman Institute in Indonesia, the University of Arizona and the University of Toulouse. The research was funded by the Royal Society of New Zealand through a Rutherford Fellowship.