Groups of monkeys living on two neighbouring islands in South-East Asia may have different cultural traditions. Both groups use stone tools, but the monkeys in one group regularly reuse them, while the other monkeys discard them 鈥� for no apparent reason.
On islands off the coast of Thailand, collect shellfish along the coasts, then use stone tools to crack them open. The macaques are one of only four primate species known to use stone tools, says Lydia Luncz of the University of Oxford. The others are humans, chimpanzees and bearded capuchin monkeys.
Luncz and her colleagues compared the tools left by monkeys at two sites just 9 kilometres apart: Boi Yai island and Lobi Bay, on the nearby Yao Noi island. The tools on Boi Yai were much more intensively used and showed extensive wear, whereas those from Lobi Bay were hardly used and needed close examination to be identified as implements. 鈥淲e can identify the group by just looking at the tool,鈥� says Luncz.
Advertisement
On other islands, such differences could be explained by external factors, like a shortage of stone. However, when the researchers scoured the beaches, they found plenty of useable stones at both sites. So the thrifty monkeys on Boi Yai weren鈥檛 recycling tools out of necessity.
This suggests that the differences might instead be cultural, passed on from monkey to monkey as they learn from each other, says Luncz. 鈥淭hat鈥檚 the first time in tool-using macaques that we are finding something like this.鈥�
It isn鈥檛 clear why one group has developed a habit of reusing stone tools. One possibility is that their group has a tendency towards thriftiness. 鈥淚 wouldn鈥檛 be surprised if that behaviour is just part of their daily behaviour in general,鈥� says Luncz. However, neither group has been studied much by humans, so we don鈥檛 know a great deal about how they spend their days.
The finding may change how we interpret the human archaeological record, says Luncz. The Lobi Bay monkeys use their tools so little that it is hard to recognise them as tools. If ancient humans also had a single-use attitude to stone tools, we might not recognise them either.
Similarly, the two monkey groups use their tools for the same purpose 鈥� obtaining shellfish 鈥� but the two sets of tools look different. 鈥淚f you find different traces on the tool, it doesn鈥檛 necessarily mean there鈥檚 a different behaviour,鈥� says Luncz.
eLife
