Depending on where a meal is served, a person might tuck in with a fork and knife, with chopsticks or with bare hands. Chimpanzees, it turns out, have a similar kind of cultural variation: Neighboring groups of the animals have unique nut-cracking styles, a new study in the journal Current Biology reports.

Researchers noted that one group of wild chimps in Tai National Park in Ivory Coast preferred stone tools to hammer open coula nuts. Two other groups of chimps used stone tools early in the season, when the nuts were harder, but then switched to wood tools as the nuts grew softer.

The chimp groups also had preferences for different sizes of wood, said Lydia Luncz, the study’s first author and a primatologist at theMax Planck Institute for Evolutionary Anthropologyin Leipzig, Germany.

The chimpanzees are displaying a sort of cultural preference with their tool choice, said Ms. Luncz, a graduate student. “It’s just a preference they have, because they grew up that way,” she said.

On occasion, when there were not enough stones to be found, the chimpanzees that preferred them would resort to using wood. “They know how to do it,” Ms. Luncz said. “They just don’t like it.”

She also noted that female chimpanzees leave their social groups at puberty to join new groups. By this time they are experts at cracking nuts. But it appears that they adopt the nut-cracking methods used by their new group, Ms. Luncz said.

“Otherwise things would get mixed up, but we see these clear differences between the groups,” she said.

Although the chimpanzee groups neighbor one another and interact often, their interactions are never friendly and they don’t learn from one another. “It’s always war,” Ms. Luncz said. “They don’t interact in a way where they could watch each other nut-cracking.”

From nytimes.com