Genetic comparisons show that Tapanuli orangutans diverged from Sumatran orangutans about 3.4 million years ago , and became more isolated after the Lake Toba eruption that occurred about 75,000 years ago . They had continued sporadic contact that stopped at least 10,000 to 20,000 years ago . Tapanuli orangutans diverged from Bornean orangutans about 674,000 years ago . Orangutans travelled from Sumatra to Borneo as the islands were connected by land bridges as parts of Sundaland during recent glacial periods when sea levels were much lower . The present range of Tapanuli orangutans is thought to be close to the area where ancestral orangutans first entered what is now Indonesia from mainland Asia
Lake Toba eruption
Toba catastrophe theory
Tapanuli orangutan