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 between 10,000 and 20,000 years ago. Tapanuli orangutans diverged from Bornean orangutans about 674,000 years ago. Orangutans were able to travel from Sumatra to Borneo because 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.