Human settlement of Madagascar didn't occur until sometime between 350 BC and AD 550 - by Austronesian peoples arriving on outrigger canoes from Borneo.
These were joined around AD 1000 by Bantu migrants crossing the Mozambique Channel from East Africa.
Other groups continued to settle on Madagascar over time, each one making lasting contributions to Malagasy cultural life.
The Malagasy ethnic group is often divided into 18 or more sub-groups of which the largest are the Merina of the central highlands.
Reference: Wikipedia