culture in chimpanzees

Blogging on Peer-Reviewed ResearchWhen Jane Goodall observed chimpanzees making tools, it became clear that here was yet another example of the continuum between humans and non-human primates. Use and manufacture of tools was not something that distinguished humans from their close relatives, & chimps could be said to have a form of culture. Now here’s a paper that presents evidence that there are cultural differences between different groups of chimpanzees.

One of the examples of tool use that Goodall  observed in the Gombe chimps was the use of a twig or grass stem to remove termites from their holes. A chimp would select a stem, check that it was the right length, and then insert the stem into a termite hole and wait long enough for some of the insects to bite onto the stem with their jaws. Then the chimp would lift out the stem & remove the termites by running stem & termites through its lips. Schoning & his colleagues (2008) looked at similar behaviour by chimpanzees preying on army ants. They’d noticed that different chimp populations used different techniques, and wanted to see if these differences in tool use were related solely to characteristics of the species of ants they were eating, or whether there were cultural differences that weren’t linked to prey characteristics. They asked, Is behavioural diversity in ant-dipping an example of material culture?

Army ant nests contain millions of the insects, so they represent a rich source of food. From time to time they move to find a new nest site, travelling in broad columns & attacking other animals with their strong (& painful!) bites. Chimps in several different areas are known to eat army ants, modifying stems or sticks to use as ant-gathering tools. (In some areas they simply scoop the ants up in their hands.)  Once the army ants have bitten on to the stick, the chimps will either wipe the insects off with a hand and transfer them to the mouth (‘pull-through’) or nibble them off the stick (‘direct-mouthing’).

The research team looking at ant-dipping by chimps at 14 different sites. They found that: the length of the tools used varied considerably between the different sites; chimps gathered ants from their nomadic columns at some sites, but only from nests at others; and at some sites didn’t even eat ants despite their being available. Previous workers had also found that the tools, & methods, used by the chimps varied depending on the type of army ant available. The chimps used longer tools for black ants, shorter tools for red ants, and tended to use direct-mouthing more for red ants. In other words, all these variables needed to be taken into account before making a decision about whether chimps from different areas really do have different cultures. In addition, the ants showed different niches: epigaeic ants (vicious when attacked) foraged both in leaf litter & up in the trees, while the less aggressive ‘intermediate’ ants foraged only in leaf litter. Schonning et al. (2008) did a large-scale comparative study on army-ant eating by chimpanzees, …to assess which army-any species are available, which species are consumed, in which contexts species are exploited, and whether or not the techniques and tools used to harvest the same species or similar species differ across sites.

Two sites, Bossou & Tai, proved to be particularly interesting. Both sites had the same species of ants, & these were all eaten by the resident chimps. But: the Tai chimps used direct-mouthing only, while Bossou chimps used both; at Bossou they used two methods of direct-mouthing compared to one at Tai; Tai chimps took ants only from columns, while at Bossou they ate from columns & nests; the tools used were siginificantly shorter at Bossou; & Tai chimps never used tools to get epigaeic ants from the nests, taking them by hand, while at Bossou they sometimes used tools & sometimes didn’t.

From all this, Schonning & his co-workers decided that the fact that chimps in some areas ate army ants, while others didn’t, wasn’t related to ant availability. In addition, the variations in size & use of tools, and the techniques for their use, couldn’t be completely explained by looking at the nature of the ant species present in an area. They concluded that our data do not show that variation in army-ant-eating is sociocultural, but our findings are consistent with the interpretation that army-ant-eating by chimpanzees varies culturally, and noted that it’s imperative to obtain as much data, in as much detail as possible, to tease out the role of genetics, environment, and learned behaviour in developing cultural diversity. Without this, any explanations may be no more than just-so stories.

C. Schoning, T. Humle, Y. Mobius & W.C. McGrew (2008) The nature of culture: technological variation in chimpanzee predation on army ants revisited. Journal of Human Evolution 55: 48-59

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