Environment

Chimpanzees are Cultural Conformists

Animals do the most amazing things. Read about them here in this series by Janaki Lenin.

A chimpanzee. Credit: Kathelijne Koops.

A chimpanzee. Credit: Kathelijne Koops.

Chimpanzees have culture. There’s no doubt about it. By culture, biologists don’t mean primates sing and dance. They say an animal has culture if a particular activity is learned by all the members of a group.

To determine if a species has culture, researchers look for any behaviour that cannot be explained by innate predisposition because of genes and opportunities provided by environment. For instance, there are four subspecies of chimpanzees in different parts of Africa. Each may do things differently. There’s evidence of culture when different groups of the same subspecies consistently performed the same action distinctly.

Primatologists Lydia Luncz and her colleagues in Germany came up with a simple solution – compare the behaviour of neighbouring groups that live in the same habitat and are close enough to be genetically similar.

Researchers led by Kathelijn Koops of University of Zurich, Switzerland, and her colleagues from Germany and Japan used this method in Kalinzu forest, Uganda.

Typically, the primates dip a stick into the nest or trail, and wait for ants swarm over it. Then they use one of two techniques. One is to swipe a hand along the length of the tool and stuff the biting mass into their mouths. Another technique is to nibble the ants straight off the stick, like we would eat a measly skewered sheesh kebab.

Chimpanzees use sticks of different length. For example, they’d use longer sticks for more aggressive ants. In Guinea, chimps use long sticks to poke into nests and short sticks for ants of the same species running along trails.

Koops and her team compared the length of stick used by two neighbouring groups – called M and S – of eastern chimpanzees. Koops says the M group was named after the Musanga trees that were common in that group’s territory, and the S group was named after the area, Sunzu.

The researchers found the sticks used by the M-group were on average 16 cm. longer than the S-group. Since these chimps were used to people, the researchers were able to watch them fishing for ants. The primates used a clever technique of ant-catching, to avoid being bitten by the formidable soldiers of the ant colony. The chimps hung suspended from an overhanging tree when sticking a long twig into the ant nest. Perhaps, fishing while hanging from trees required longer sticks to reach deep into the nest. What’s more, the length of the ant-fishing stick has remained constant since 1997.

The other S-group was shy and researchers could not observe them at dinner. They could only measure the length of the sticks they found lying near ant nests in that group’s territory. These chimps used shorter sticks to fish for the same species of ants. In fact, they were far shorter than sticks made by other chimp groups.

The researchers say it’s possible this group nibbles ants directly from the stick. None of the nests that the S-group raided had a tree nearby, so it’s unlikely they dangled from one while poking the nest. The researchers speculate that there may be differences in the ant nests in the territories of the two groups. Perhaps the ant nests were not deep or the ants were not aggressive enough.

Kathelijne Koops told The Wire,One possible criticism [of the study] could be that the data for S-group are relatively limited and the difference in tool length could potentially reflect a different prey preference in this community. However, even if S-group differs in army ant species preference, this would still mean that there is a cultural difference between the two communities, because prey availabilities are identical.”

In chimp society, there is little social interaction between neighbouring groups. There is no scope for one group to learn from its neighbours. On reaching sexual maturity, the boys stay home, while the girls leave to join other groups. No matter what their natal group did, once these immigrants join a new group, they imitate and adopt the group’s behaviour. Eventually, there’s no difference in ant-fishing techniques between females and males of the same group. This is the clincher in the evidence of culture.

Evidence of culture from Kalinzu is not new, as primatologists have already established chimp culture in the Ivory Coast in 2012. Lydia Luncz and her colleagues from the Max Planck Institute of Evolutionary Anthropology, Germany, studied three neighbouring groups of western chimpanzees. Those chimps differed on 27 different activities such as how they used tools, what they ate, how they hunted, and how they interacted with one another.

So what is special about this study?

Luncz told The Wire, “Finding such sophisticated cultural diversity in another subspecies of chimpanzees, besides the western chimpanzee, means that this ability of creating and maintaining differences between neighbours already existed before the split of chimpanzee subspecies. If this behaviour is found to be universal in all chimpanzee communities, the likelihood increases that it was already shared with our last common ancestor about 5 to 7 million years ago.”

Not all eastern chimpanzees use sticks or eat ants. Thibaud Gruber, from the University of Neuchâtel, Switzerland, told The Wire, “These findings in Uganda, where I also work, make me wonder why our Budongo chimps, a few hundred kilometres away, are so limited in their own tool set. They do not display any ant-fishing, or stick use, for that matter. One hypothesis is that the Budongo communities lost stick use for an ecological reason. Our chimps do not feed on ants at all, and on hardly any termites. Ants are just not part of their diet. Actually, in this respect, Kalinzu is unique in Uganda.”

Kalinzu is unique for another reason too. Koops says, “Our study is the first to find a difference in tool manufacturing between neighbouring groups.”

The paper, ‘Cultural differences in ant-dipping tool length between neighbouring chimpanzee communities at Kalinzu, Uganda‘, was published in Scientific Reports on July 22.

Janaki Lenin is the author of My Husband and Other Animals. She lives in a forest with snake-man Rom Whitaker and tweets at @janakilenin.