Due to fluctuating sea levels, mainland Eurasia was not separated completely from the western part of the Indonesian archipelago, allowing animals from the Eurasian mainland passage to the archipelago, and new species evolved.
Mainland Eurasia was not separated completely from the western part of the Indonesian archipelago. This was due to fluctuating sea levels. Mainland Eurasia was allowing animals from the Eurasian mainland passage to the archipelago. This was due to fluctuating sea levels. New species evolved. This was due to fluctuating sea levels.