“Mystery Monkey” Discovered in Borneo, Scientists Worried


| LAST UPDATE 05/26/2022

By Hayden Katz
monkey mystery borneo hybrid
Future Publishing / Contributor via Getty Images

Around six years ago,  Brenden Miles was working as a tour guide showing travelers around the Kinabatangan River in the Malaysian part of Borneo. One day he stumbled upon a monkey that looked especially odd. Miles took a couple of pictures of the animal and went on his way, not thinking much of it. As it turned out, the mysterious ape was a very rare hybrid of two faraway related primate species that have the same fragmented habitat. Here's why scientists are concerned about this discovery.

When Miles was finally back at home, he began scrolling through his camera roll when he saw the mysterious ape. "At first, I thought it could be a morph of the silvered leaf monkey," Miles said, referring to a member of the species with rare color variation. But that all changed when he took a closer look at the monkey's features. "Its nose was long like that of a proboscis monkey, and its tail was thicker than that of a silvered leaf [monkey]," he recalled. 

mystery monkey borneo hybrid
Future Publishing / Contributor via Getty Images
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After scientists analyzed the pictures, they reported in the International Journal of Primatology that this offering came to be from a male proboscis monkey (Nasalis larvatus) and a female silvered leaf monkey (Trachypithecus cristatus). This rare hybrid can be concerning because when two closely related organisms mate, it signals that there is a disruption in their environment. “Different species — even from the same genus — when they share a habitat, they may interact with each other, but they may usually not mate. This kind of cross-genera hybridization happens only when there is some ecological pressure,” said Ruppert of the Universiti Sains Malaysia in Penang Island. “In certain areas, both [monkey] species are confined to small forest fragments along the river,” Ruppert says. This leads to competition for food, mates, and other resources. “The animals cannot disperse and, in this case, the male of the larger species — the proboscis monkey — can easily displace the male silvered leaf monkey.”

Since it was first spotted, the mysterious monkey had been seen a few times roaming around in the state of Sabah, causing even more worry for Ruppert. “The hybrid is gorgeous, but we don’t want to see more of them,” he explained why. “Both species should have a large enough habitat, dispersal opportunities, and enough food to conduct their natural behaviors in the long term.” If there is habitat loss or fragmentation occurs in Borneo, that could mean that climate change is changing the land, meaning more closely related species will start to mate. This is not ideal of course, but scientists are still unsure what should be done. Stay tuned for updates. 

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