Between approximately 2.5 and 3.5 million years ago, humans entered the Stone Age when they started using rocks as tools. Now, at least one group of white-faced capuchin monkeys in Panama has followed suit.
Researchers have discovered that one population of white-faced capuchin monkeys in Panama have entered the Stone Age according to a study published in bioRxiv.
The monkeys have started using stone tools to break nuts and shellfish, making them the fourth type of primates to do so after us.
Other nearby populations don’t make use of stone tools, which might suggest that primates – perhaps including our ancestors – stumble into the stone age by chance.
“We were surprised that this behaviour appears to be geographically localised,” lead author Brendan Barrett at the Max Planck Institute for Ornithology told NewScientist.
Researchers can’t say for sure how long these monkeys have been using stone tools, but the behavior was first noted back in 2004 when a co-author, Alicia Ibáñez, spotted it happening on the island.
In 2017 researcher went back to the area and placed cameras across Jicarón and two nearby islands in hopes of actually capturing the monkeys at work. Sure enough, over the course of a year, tool use was recorded on Jicarón on 205 days, indicating that this is a regular practice.
“At the most active tool use site, 83.2% of days where capuchins were sighted corresponded with tool use,” the study said.
The team witnessed the male monkeys break coconuts, crabs, and snails. However, it is unclear why this behavior is not more spread out to other groups on the island. The researchers note that individual monkeys move between groups, so in theory the innovation should spread.
The team suggest that it is possible that entering the Stone Age has a chance component to it, rather than being an expected trajectory for primates. Perhaps, for example, a smarter-than-average individual began using the tools and the others copied him. Given limited food options, tools can increase their chance of survival.
Though primates in the wild have been documented using objects like sticks for tools, the capuchin monkeys in question join just a handful of other non-human primates who have entered their own kind of stone age. They are only the second American species and the fourth overall. Others include certain chimps in West Africa and certain macaques in Thailand, while another group of capuchin monkeys from South America that uses stone tools may have been doing so for some 700 years.
The capuchin monkeys described in the new report likely joined this small group of non-human primates able to use tools because of the specific conditions in which they live. These monkeys are “highly terrestrial, under decreased predation pressure and potentially experience resource limitation compared to mainland populations,” the study states, explaining that these are “three conditions considered important for the evolution of stone tool use.”
The team hope that more research and further observations of these monkeys will help explain what is going on.
