The crab-eating macaques of Thailand and Burma are notoriously clever. Using various stone tools, they are able to pry open nuts, oysters and sea snails along the Andaman coast, and around the shores of smaller islands, with brutal efficiency. Some of them have even managed to work out that they can use human hair as dental floss for their teeth – all this, despite having far smaller brains than us humans.
Writing in the Journal of Human Evolution, a team of researchers have pointed out that tool use in Old World nonhuman primates, including these macaques, has only been documented with living animals; until now, no-one has looked for any archaeological evidence of this type of activity. Although it’s reasonable to assume that tool use in macaques has been occurring for multiple generations, there is currently no evidence that shows this is demonstrably true.
“What we don't have at the moment is a body of archaeological evidence to compare the evolutionary behavior of other primates with our own,” the study’s lead author Michael Haslam, from the School of Archaeology at the University of Oxford and leader of the Primate Archaeology (Primarch) project, said in a statement. New excavations reveal that they have been in the Stone Age for at least 50 years.
Macaque versus oyster shell. University of Oxford via YouTube
For this study, groups of Macaca fascicularis aurea (crab-eating macaques) were carefully observed on the Thai island of Piak Nam Yai. These opportunistic omnivores eat whatever may be available to them at the time, but unlike many other animals, they have the capability to use stone tools – mainly ones used to fracture or crush things – to aid their foraging.
After spending some time observing these macaques using their various stone implements, the researchers noted that they often left their tools near piles of discarded oyster shells. One remarkably ravenous macaque ate 63 oysters in a row, and left his stone tool beside his tower of shells after he decided that he couldn’t possibly stomach another. Scratch marks on the boulders, specific fracture marks on shells, and indent marks on the tools were also common indicators of tool-use activities.