Cultural heritage may influence tool choice by capuchin monkeys, study finds

Capuchin monkeys are some of the few primates to use tools on a daily basis. One of the main uses in the Cerrado and Caatinga are stone hammers and anvils, which are used to break the shell of hard foods, such as jatobá pods and cashew nuts.

In a study published in the journal Scientific Reports, Brazilian researchers showed that the correlation between food hardness and tool size is not always accurate as previously thought.

By observing three Brazilian populations of capuchin monkeys of the Sapajus libidinosus species and measuring the strength of the resources, the size and weight of the tools used and the availability of stones at the site, the scientists concluded that the culture of the group —information maintained over generations by social learning—may also influence choice.

“In one of the three populations analyzed, even when they have stones that are more suitable for a given resource, they can use disproportionately heavy tools, which may indicate a cultural trait of that group”, explains Tiago Falótico, a researcher at EACH-USP (Escola de Artes, Sciences and Humanities of the University of São Paulo) supported by FAPESP.

The population to which the researcher refers lives in the Chapada dos Veadeiros National Park, in Goiás. The comparison was made with two others, residing in Piauí: in the Serra das Confusões National Park and in the Serra da Capivara National Park, 100 kilometers away from each other.

The tools, in this case, refer to pieces of quartzite and sandstone rock found in places known as breakout sites. Animals frequent these places exclusively to gain access to these hammers and anvils. The first ones are beaten by the monkeys against the food, which is supported by the anvils.

“In Serra das Confusões, when breaking small and less resistant fruits, capuchin monkeys use smaller tools. When they need to open larger and hard coconuts, they use large and heavy hammers. In Chapada dos Veadeiros, even though they have a variety of tools, they use the heavier even for more fragile foods”, says the researcher.

Not by chance, it was in Chapada dos Veadeiros that researchers recorded the heaviest weight ever lifted by capuchin monkeys. An individual of these small primates, which weigh 3.5 kg on average (adult males), was filmed lifting a 4.65 kg hammer. “They are true bodybuilders”, notes Falótico.

Measurements

The results are the result of meticulous work. In the three places where the studied populations of capuchin monkeys live, the foods most found in the breaking sites were documented, such as babassu coconut, jatobá, cashew nuts and maniçoba seeds (a close relative of cassava).

The availability of stones was also documented, in addition to the size and weight of the tools found. With a special apparatus, the researchers also measured the resistance of each food found. Finally, they observed and filmed how the monkeys from each of the populations used the tools with certain foods.

“We expected to find a very direct correlation between the size and weight of the tool and the food, but the population of Chapada dos Veadeiros, which has a great availability of rocks and could choose bigger or smaller, predominantly uses the bigger ones. This behavior is probably inherited. ancestors, a cultural differentiation from other populations”, says Falótico.

Another example that monkeys have cultural learning is that, in other regions of Brazil, such as Serra de Itabaiana, in Sergipe, and Chapada Diamantina, in Bahia, there are also capuchin monkeys of the same genus, stones and the same fruits available. . However, there are no breakage sites and, therefore, the behavior of opening the fruits to eat. In Serra das Confusões, the monkeys break down various foods, except cashew nuts, although they are abundant.

“It is not just the availability or scarcity of resources that defines the occurrence of the behavior, but the cultural heritage”, he says.

The researchers are now performing genetic analyzes of the three populations to see if cultural differences can be detected in the genome.

The work was also supported by FAPESP through a scholarship granted to Tatiane Valença at EACH-USP.

ways of man

In another work, published in the Journal of Human Evolution, Falótico and a team of archaeologists from Spain, Germany and the United Kingdom analyzed, in a field experiment, the formation of stone chips by capuchin monkeys when they used different types of rock as anvil.

In nature, fragments are formed when these primates hit one stone against another to use the powder produced to rub on their bodies and teeth. It is not known what capuchin monkeys use this product for, but researchers believe it may have an effect against parasites. In the experiment, the anvils’ shattering of more homogeneous material also created these types of chips.

The chips, however, are not used by the monkeys, although they are very similar to the lithic tools found in archaeological sites in various parts of the world. The researchers hypothesize that, before intentionally creating slivers to use as tools, early humans got them by accident.

“In the same way, in theory, capuchin monkeys could start using chips in the future, if an innovative individual starts using them and the others learn by watching. Therefore, these primates can be a model for understanding human evolution”, he points out. the Brazilian.

In a previous work, the group showed how the lithic tools used by the population of capuchin monkeys in Serra da Capivara gain specific marks according to use (read more here).

Comparing the marks on ape and hominid tools may help to unravel how early humans used these lithic tools. With this, Brazilian capuchin monkeys pave the way for better understanding of our ancestors.

The article Stone tools differences across three capuchin monkey populations: food’s physical properties, ecology, and culture is open access.

And the study A primate model for the origin of flake technology can be read here.