By Rebecca Morelle
BBC News science reporter
The dramatic collapse of orangutan populations has been linked to human activity, new genetic evidence shows.
Deforestation has had a huge impact on orangutan numbers
Researchers report that a population crash occurred during the past 200 years, coinciding with deforestation in the same area.
The study focuses on orangutans found in the forests of Kinabatangan Wildlife Sanctuary in Malaysia.
Writing in the journal Plos Biology, researchers suggest that the outlook is "bleak" unless urgent action is taken.
The team looked at 200 orangutans living along the Kinabatangan river. These animals are confined to fragmented patches of forest.
By collecting the orangutans' hair and faeces, the researchers were able to extract DNA to create genetic profiles, which could then be used to study genetic diversity.
Professor Michael Bruford, a senior author on the Public Library of Science journal paper and a conservation biologist at Cardiff University, told the BBC news website of his surprise at the results.
"The genetic diversity of the population showed a very strong signal of a massive population decline," he said.
"This was interesting because we didn't expect it to show that the decline has happened so recently - within the last 200 years."
The period in which the population collapse occurred correlates strongly with the time that the colonial power began to exploit the habitat.
When north Borneo became part of the British Empire in the late 19th Century, deforestation began in earnest.
In recent years, conservationists have linked the orangutans' decline to forest clearance for palm oil plantations, which produce the raw materials used for products like lipstick and soap.
However, the Malaysian authorities told the BBC in November that the plantations were mainly grown on land that had already been cultivated or in "secondary jungle".
Environmental impact studies were also carried out before any plantations were established, they added.
Orangutans numbers are now put at just 50,000, according to The World Atlas of Great Apes and their Conservation which is published by the UN's environment and biodiversity agencies.
Professor Bruford warns that the animals' habitat needs to be better preserved, and that steps should be taken to re-establish corridors between fragmented forest patches.
He says it may even be necessary to move orangutans around to prevent inbreeding.
"The important thing you have to remember is that Kinabatangan is just one area, but these problems are significant in all orangutan ranges.
If we don't put these changes in place throughout, then the outlook is really very bleak indeed," he urged.