The genetic side to chimpanzee culture

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If you watch chimpanzees from different parts of Africa, you’ll see them doing very different things. Some use sticks to extract honey from beehives, while others prefer leaves. Some use sticks as hunting spears and others use them to fish for ants. Some drum on branches to get attention and others rip leaves between their teeth.

These behaviours have been described as cultural traditions; they’re the chimp equivalent of the musical styles, fashion trends and social rules of humans. They stem from the readiness of great apes to ape one another and pick up behaviours from their peers. But a new study complicates our understanding of chimp cultures. Kevin Langergraber at the Max Planck Institute for Evolutionary Anthropology has found that much of this variation in behaviour could have a genetic influence.

Langergraber studied almost 250 chimps, who came from 9 groups, including 3 from the west African subspecies and 6 from the east African one. For each one, he noted whether they performed any of 39 different behaviours, and he sequenced DNA from their mitochondria (small energy factories in animal cells that have their own small accessory genome).

Langergraber found that the differences in their genes were mirrored by differences in their behaviour. Groups of chimps with starkly differing cultures are also genetically distant and the greater the gap between their behaviours, the greater the gap between their genes. And only a small number of actions varied between groups that were genetically similar.

Frans de Waal, a renowned chimp researcher from Emory University, praises Langergraber’s work. “[It] is not dismissive of the culture concept, but adds a complication to the picture,” he says. “The data now indicate that chimpanzees, which are genetically incredibly diverse, have an overlap between genetic and cultural diversity that will need to be addressed. It is wonderful data, and makes the culture story all the more fascinating.”

These new results don’t mean that chimp cultures are all “in their genes”. After all, many of the behaviours that have fallen under the banner of chimp culture are complex traits that are unlikely to be genetically determined. “No one would assume a gene for ant-fishing in the chimpanzee in the same way that no one would assume that some humans have a knife & fork gene and others a chopstick gene,” says de Waal. “However,” adds Langergraber, “it is possible that groups differ in the frequency of [genetic variants] that lead (however indirectly) to differences in the propensity and predispositions for individuals to fish for ants.” They might be more dextrous, for example, or like the flavour of ants.

Nor does Langergraber’s work downplay the role of culture in explaining the varied behaviours of chimps. For a start, both he and de Waal note that you’d get the same results if you looked at humans, and no one would think less of our culture as a result.  De Waal also says, “The finding is consistent with culture spreading from group to group by female migration, which may be based on learning but still would produce a correlation with genetics.”

Many previous studies have shown that apes (and probably even monkeys) can imitate and learn from each other. As a result, traditions and habits can spread in non-genetic ways. This is the essence of culture, and it means that individuals and groups end up behaving in varied ways. But the key message from Langergraber’s work is that it’s not clear how much of this variation in the wild is a result of cultural traditions.

If anything, the main message from the study is that the methods primate researchers use need to be improved. Consider one of the landmark studies in this field: a paper from 1999, in which Andrew Whiten and Jane Goodall documented 39 chimp behaviours that were common in at least one group but absent in others. The duo reasoned that this variation wasn’t down to differences in the chimps’ environment – for example, some fished for termites and others didn’t, even though both groups had access to these insects.

This line of reasoning is called the “method of exclusion” and it’s commonly used in the field. Researchers infer the existence of cultural traditions by ruling out other explanations. The trouble with the approach is that while scientists typically exclude ecological explanations (like the presence of termites), genetic ones tend to slip under the radar.

An alternative might be to look at how differently individuals behave within the same group, depending on how closely related they are. Are close relatives more likely to act in the same way, or are such parallels more common among chimps who interact with each other more frequently? Langergraber also says that you can often tell how a behaviour was transmitted by looking at how it spreads through a group. If they’re imitating one another, the behaviour gets picked up very quickly in a short space of time, as the number of potential tutors suddenly skyrockets. These accelerating patterns are a sign of social learning at work.

Reference: Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2010.1112

Image by Delphine Bruyere

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