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June 18, 2009

Honey-Loving Chimps Handy, Too

Life for human evolution researchers was so much simpler 50 years ago. There seemed to be a clear distinction between the cognitive capacities of humans and that of all other animals. The proof: Humans made tools, other species did not. The concept was perhaps best expressed in the title of a 1949 book by British anthropologist Kenneth Oakley, Man the Tool-Maker. As late as the early 1960s, most researchers agreed with famed fossil hunter Louis Leakey that toolmaking was a uniquely human activity.

But with more and more scientific observations of primates, identifying “uniquely human” behavior has been getting harder and harder. A paper in the June Journal of Human Evolution now extends animals’ reach even further toward human abilities, reporting that wild chimpanzees can sequentially craft a set of tools for a single task. Primatologist Christophe Boesch and his colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, conclude that researchers might have to rethink their whole approach to the cognitive divide between humans and their primate cousins.

Back in the early 1960s, that divide was still unbreached. Then in 1964, Leakey’s protégée Jane Goodall reported that chimpanzees at Gombe Stream National Park in Tanzania stripped leaves off twigs and used them to fish termites out of their mounds. Score one for the chimps. But the twigs were simple tools. Unlike humans, chimpanzees didn’t have tool kits with different tool types, did they? Well, it turned out they did. And since the 1970s, chimps at sites such as Gombe, the Taï National Park in Côte d’Ivoire, and Mahale Mountains National Park in Tanzania have been observed using up to 25 different kinds of tools for different functions.

Indeed, as soon as researchers proposed new ways in which human tool use was unique, their hypotheses got shot down by new observations. Like humans, some chimps need tools to survive when food is scarce. Chimp tools can vary from region to region according to purely cultural considerations, for example, in the different ways they use leaves and branches to catch ants. And chimps can use tools to access food hidden underground, which requires mentally visualizing things they cannot directly see and then trying to access them. One of the last bastions of alleged human uniqueness has been the assumption that chimps don’t combine a number of different tools together, by using one after another in serial fashion, to attain a single, primary goal—something thought to demand great cognitive power.

In 2005, Boesch, who has been watching chimps in West Africa for many years, began working at a new chimp site, Loango National Park on the coast of Gabon. The chimps here, though they don’t crack nuts like those elsewhere, love honey. And they go to great lengths to find it, seeking out the hives of both tree-dwelling and underground bees, according to dozens of hours of observations by Boesch and his co-workers, as well as analyses of 400 tools left around beehives. The researchers found that the animals create as many as five different tool types and use them one after the other to get at the honey. On one occasion, the team observed nine chimps surrounding a large beehive in a tree and making different tool types over a period of nearly 80 minutes.

All the tools are made from tree branches or bark, but they have distinct functions: “pounders” to break open tree-bound beehives, “perforators” to locate underground beehives, “enlargers” to penetrate and enlarge a hive’s compartments, and “collectors” and “swabbers” to scoop out the honey.

Observations of chimps using such tool sets have been very rare until recently, although there have been preliminary sightings at a few other sites, the team says in its report. The researchers were particularly impressed by the elaborate way in which the Loango chimps use tools to find underground beehives, which are often a meter under the ground and not directly under their openings to the surface. Boesch found that it took him 20 to 40 minutes to perform the same task, which requires, the authors say, “a precise three-dimensional sense of geometry.”

Boesch and colleagues are not claiming that chimps are as cognitively advanced as humans, of course, although they point out that chimps’ “flexible and complex” tool use is not seen in any other animal species, even though other mammals and some birds use tools as well. And there is still one frontier that chimps have not been observed to cross: They do not use tools to make other tools, as even the earliest humans did when they used one stone to fashion a tool out of another.

Nevertheless, the new observations suggest that the key difference between chimp and human toolmaking ability might be “one of quantity rather than quality,” the authors write. That makes sense to at least one tool expert I sent the paper to, archaeologist Dietrich Stout of University College London (who is soon to move to Emory University in Atlanta). “It is past time to give up on the idea that there is going to be some simple, qualitative statement that fully encapsulates what is unique about human tool use,” Stout told me.

—Michael Balter

Credit: Christophe Boesch/MPI EVA

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