June 28 (UPI) -- For thousands of years, the evolution of orangutans has been influenced by humans, according to a new study.
"It was often assumed that environmental factors like fruit availability were primarily responsible for most features of modern-day orangutans, such as the fact that they usually live at low densities and have a restricted geographic distribution," Stephanie Spehar, an associate professor of anthropology at the University of Wisconsin Oshkosh, said in a news release.
However, fossil evidence of the orangutan lineages of Southeast Asia suggest the apes began adapting to life alongside humans as early as 70,000 years ago.
"Our synthesis of fossil, archeological, genetic and behavioral evidence indicates that long-term interactions with humans shaped orangutans in some pretty profound ways," Spehar said.
Fossils collected in China, Thailand and Vietnam suggest the apes were more widespread and lived in denser populations. These early lineages likely also adapted to a wider range of habitats.
Analysis of the fossil timeline showed shifts in distribution and population dynamics among early orangutan lineages correspond with changes in human behavior. Scientists found a sharp reduction in the ape's numbers followed the emergence of projectile weapons around 20,000 years ago.
"It suggests that Paleolithic humans were probably hunting orangutans regularly -- and as orangutans reproduce very slowly, it doesn't take much to put a dent in their populations," Spehar said.
The fossil and genetic analysis suggests the orangutan nearly suffered the fate of the woolly mammoth and other megafauna, and that a shift in behavior may have enabled ape's survival.
"Surviving orangutans probably modified their behavior to counter this threat, perhaps retreating further into the thickest forests to avoid human hunters," researchers wrote in The Conversation.
The latest findings, published this week in the journal Science Advances, suggest humans have been underestimating the orangutan's adaptability. For example, recent camera trap surveys suggest the apes, thought to be strictly arboreal, spend a surprising amount of time walking around on the ground.
Researchers say more work must be done to understand whether orangutans can thrive in different kinds human-altered habitats. Some studies have shown the apes can maintain healthy populations on oil palm plantations and in selectively-logged forests.
There may be unique conservation opportunities for orangutans that humans are currently ignoring.
"This offers hope," said Marc Ancrenaz, director of French conservation group Hutan. "If we humans manage things correctly, there can be room for the orangutan in the Anthropocene."