Macaques choose stone tools based on own size and strength

Macaques appear to select stone tools to crack open oil palm nuts based on the size and strength of their own body, rather than the optimum weight and size of the stone, to make the process more efficient, according to new research led by UCL. In the paper published in the Royal Society Open Science, researchers from UCL, the University of Oxford, Oxford Brookes University, Chulalongkorn University (Bangkok, Thailand) and Nanyang Technological University (Singapore), have, for the first time, described the stone tools used by wild long-tailed macaque monkeys in southern Thailand to crack open nuts. "The stone tools we've uncovered show a high degree of battering and crushing on most surfaces. Interestingly, the stone tools are smaller than those used by wild chimpanzees for processing the same nut, and are smaller than those used by wild macaques to process another encased plant food, sea almonds." said study lead Dr Tomos Proffitt (UCL Archaeology).  "These new findings should help us to understand and compare skill levels between macaques and chimpanzees during tool use, and to assess differences in tool selection and mode of use." added Dr Proffitt. The research team say this is an important step forward in the emerging field of primate archaeology, as it increases our understanding of how different non-human primates use stone tools in the wild, and may allow future insights into how early human ancestors developed and used stone tools. To date only chimpanzees in Western Africa have been observed to open oil palm nuts using a stone hammer and anvil, a behaviour some have suggested may be similar to the one that lead humans to develop stone tool technology nearly 3.3 million years ago.