Key Human Evolutionary Behavior Observed in Gorillas – Science et Avenir

It’s a gesture of two stones knocking against each other without breaking: this key behavior of human cognitive evolution has been observed in western gorillas, according to a study published in the journal Nature.

“Punch” and “percussion” with bare hands

Our ancestors went through several stages before they learned how to make stone tools. “Hitting with bare hands” is considered a prerequisite for “hitting with bare hands”. The latter allows you to make sharp fragments from a stone core. The first artifacts obtained played a fundamental role in human evolution.

The researchers closely followed the daily lives of two groups of gorillas, or 23 individuals, in the Republic of the Congo. They were especially interested in their eating habits, which they filmed. In almost 300 minutes of recording, only five episodes of “bare-handed strikes” were recorded in two gorillas. In the middle of the meal, two young monkeys did not use stones, but pieces of a termite mound, which they knocked against each other.

When feeding on termites, gorillas typically use two methods. They can directly lick the surface of termite mound pieces, tear them off or crush them (this is the “rubbing” technique). How is this technique different from “strike with bare hands”? “Blow” consists in holding a piece of termite mound with a hammer in one hand, while the other hand is empty. Two young western gorillas got creative by holding a piece of termite mound in each hand. “Adults are much more conformist,” smiles Shelly Masi, a research fellow at the National Museum of Natural History. “Their intention was certainly not to create sharp tools, but to dig up more termites,” she explains to Science et Avenir. “The important thing is that they had a goal and they voluntarily took a new action for it.” achievements”.

Researchers do not expect tools per se

This is not the first time this behavior has been observed in the wild. Japanese macaques (Macaca fuscata), far more distant from our lineage than gorillas, have already performed this gesture. For scientists, modern primates provide an opportunity to better understand the factors necessary for the emergence of stone tool production. However, the next step in this process, bare-handed percussion, requires additional qualities such as strength and precision.

Thus, this could be an important turning point in human evolution. Sometimes shards are accidentally formed when the monkeys are holding rocks. The bearded sapaju (Sapajus libidinosus) produce them regularly but never use them. In fact, there are several examples of stone manipulation in untrained primates. The exception is long-tailed macaques (Macaca fascicularis). They dig up axe-shaped stones to open shells.

Gorillas use few tools

There are very few examples of tool use among gorillas. Westerners use pseudo-tools like grass and sticks to scare off intruders. Some of them used a stick to measure the depth of the pool before crossing it. In the wild, it is the species that uses the least items among the great apes. “Being the largest primate, the gorilla doesn’t need tools, it can just use its power,” says Shelly Masi.

Emmanuelle Puideba, Director of Research at CNRS, who was involved in this study, explains to Science et Avenir: “One thing is certain, this is not a cognitive problem, because in captivity they are very good at tool tasks. They can use sticks to retrieve food. hidden in labyrinths”. Why such a difference in behavior? According to the researchers, this may be due to the “captivity effect”. That is, even if people do not directly intervene, for example, in learning, the fact that they are not in natural conditions, gives rise to a different attitude on the part of animals.

Capuchin capuchins produce and use sharp stones

The brown capuchin (Sapajus apella) is the only primate species that deliberately makes sharp shards and uses them spontaneously without training. According to a study published in the International Journal of Primatology, people have used these carved stones to receive an award. Given the lack of instructions or training in these monkeys, the researchers concluded that brown capuchins have “natural sensory, motor and cognitive abilities to make and use carved stones.”

A study of western gorillas highlights the feeding motivation of the “hit with bare hands” behavior observed in two young primates from the Republic of the Congo. According to the scientists, this foraging context may have initiated this gesture in the last common ancestors of gorillas and humans.

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