We are now accidentally making monkeys dumber

The use of stone tools is incredibly rare, so much so that it was once thought to be the exclusive domain of humans and our ancestors. Fellow apes like chimpanzees and baboons have since been proven to use stones as tools, but only a couple non-ape primates are known to do it. But now human encroachment might rob one species of this rare knowledge.

The Burmese long-tailed macaques, found on the Andaman coast of Thailand, frequently use stones to crack open the shells of favored foods like oysters and crabs. As rare as this skill is in the animal world at large, it's common practice among the macaques — in one population, 88% of all members used the stones to break shells. But that skill is now in serious jeopardy in the wake of human expansion into the macaques' habitat or, more specifically the expansion of humans' dogs into the habitat. In the aftermath of the devastating 2004 tsunami, people have illegally started using the protected coastal areas favored by macaques as the site of new farms , and the farms' guard dogs routinely scare away the macaques from the beaches that they need to visit in order to learn tool use in the first place.

Talking to the BBC, Dr. Michael Gumert of Singapore's Nanyang Technological University explains the problem:

"What's been happening is that over the past six years on the island, we've just seen more palm oil and rubber farms being developed in the forest. I've begun to notice that the groups that are closest to human activities, just aren't having kids anymore... The monkeys come down to the big rocky coasts and pick up rocks and crack things like oysters and crabs. But if the dogs repel them, the monkeys use the shore less and less and they will stop using tools as much. What we're looking at with these stone-tool-using monkeys is a rare case of truly wild long-tail macaques doing their original wild behavior, unlike most of the other macaques that have had their behavior destroyed by human development. If we develop right next to them, they will stop going to the coast to feed and go to the local rubbish bin and find food there."

The macaque population itself isn't under threat from human encroachment, so the long-term environmental impact of this development could be relatively minor. Still, the relatively sophisticated use of stone tools is something that has evolved only a handful of times in the history of our planet. We humans already don't have the most sterling reputation, so it's probably best if we could avoid accidentally making another species ignorant of this remarkable skill.

Oryx via BBC News. Image of macaque by Moyan_Brenn_BE_BACK_IN_SEPTEMBER on Flickr.