The two populations are separated by a mountain range and a fairly arid region to the west of the range.
The island is dominated by a central mountain range including 95 peaks of 3,000 m or more.
The only prominent mountain range in the lowlands, this area receives the highest rainfall and has the coolest temperatures in the region.
A peculiarity is the giant mountain range, whose inner cliffs introduce a half-circle of shadow into the zone lighted from the left.
This land form, situated at the base of a mountain range, is formed by earth and rubble carried down by mountain streams.
A piedmont zone of c. 40 km in width separates the mountain range from the eastern plains (elevation ranging from 100 to 200 m).
The riimaybe that were living in villages in the mountains and along the mountain range also enjoyed more freedom.
Significant differentiation was found across the mountain range, but the genetic composition was similar amongst populations of each side.
