The following is quoted from the book "Nomads of the Dawn". You will find information about this book at the end of the main text.
The forests of Southeast Asia originated long before the extinction of the dinosaurs and have flourished continuously for approximately 180 million years. During the Pleistocene glaciations, when global climate change transformed much of the equatorial African and Amazonian rain forest to dry land savanna, Southeast Asia's rain forests, surrounded by water, retained their moist climatic regime. Millions of years of evolution, uninterrupted by major climatic transformations, has resulted in what may be the most diverse and complex forest on earth.
The island of Borneo rose from the sea only fifteen million years ago, and during the Pleistocene, when sea levels dropped as polar ice caps expanded, a land bridge formed to the mainland of Southeast Asia. As a result Borneo was colonized by the ancient forests. Since that distant era, the climate and geology of the island have remained remarkably stable, and this, together with a lack of volcanic activity or typhoons, has left the forests relatively undisturbed for millennia. Until this century, human impact has been slight and largely limited to the shifting fields of swidden agriculturalists who dwelt on the coast and in the broad river valleys of the interior. The forested hinterland has remained, until now, largely unscathed. Go to next section of main text