Capuchin monkeys are among only a few species of primates that use tools in their daily activities. For instance, they use stones as hammers and anvils to crack open cashew nuts and other hard foods. Although scientists have long thought that tool size correlates with food hardness, a new study led by the University of São Paulo has found that this is not always the case.
By observing three populations of bearded capuchin monkeys (Sapajus libidinosus), and measuring food hardness, tool size and weight, and local availability of stones, the experts discovered that culture – defined as the knowledge passed on from one generation to the next – can also influence tool choice.
“In one of the populations we analyzed [which lives in Chapada dos Veadeiros National Park in Goiás, a state in Brazil’s central-western region], even when they have stones that are suitable for use on a particular food resource, they may use disproportionately heavy tools, possibly evidencing a cultural trait of that group,” said Tiago Falótico, a primatologist at the University of São Paulo.
The scientists compared this population with capuchins living in Serra das Confusões National Park, in Piauí, a state located in Brazil’s northeastern region, and another population from Serra da Capivara National Park, about 100 kilometers away in the same state.
“In Serra das Confusões, they use smaller tools to open smaller and softer fruit but use large, heavy hammers to crack coconut shells, which are very hard. In Chapada dos Veadeiros, where there are stones of varying sizes to choose from, they use the heaviest ones even for fragile foods,” Falótico reported.
“We expected to find a very close correlation between the type of food and the size and weight of the tool, but the population in Chapada dos Veadeiros mainly used the larger ones even though stones of all sizes are plentiful and they can choose a smaller size. They probably inherited this habit from their ancestors. It’s a cultural difference compared with the other populations. Their behavior isn’t due to the availability of resources but to cultural heritage.”
In future research, the scientists aim to analyze the genomes of all three capuchin populations in order to assess whether the cultural differences involved in their tool usage could be linked to underlying genetic differences.
The study is published in the journal Nature Scientific Reports.
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