SOME 4000 years ago, chimpanzees were using stone tools to smash nuts in the west African rainforest. The discovery, the earliest known use of technology by chimps, could indicate we share a common tool-wielding ancestor. It also opens the door to archaeological studies of chimpanzee tool use.
When Julio Mercader of the University of Calgary, Canada, and his colleagues dug out a 4300-year-old site in Tai National Park, Ivory Coast, they found a variety of worked stone fragments. A few are clearly of human origin, as they show systematic efforts to flake rock to form edges. However, most of the fragments resulted from the kind of cruder bashing action that chimps and humans use to crack nuts.
When Mercader and two colleagues reconstructed the original stone tools from which the fragments came, they found that most were relatively large, weighing an average of 710 grams. This is larger than tools used by Stone Age humans, but a similar size to the hammer stones used by modern-day chimps.
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Moreover, from the shape and size of the starch grains in plant residues lodged in crevices in the stones, Mercader concludes that most came from nuts rather than tubers or legumes. Many of these nut species are eaten by modern chimps, but not human hunter-gatherers. Putting the two lines of evidence together, he reckons that the site represents an ancient feeding area where chimpanzees used stone tools (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0607909104).
The possibility that chimpanzees used tools so long ago lends support to the idea that humans and chimps inherited tool-using skills from a common ancestor. “The simplest, most parsimonious explanation to having two lineages using bashing technologies is that they both inherited it, rather than inventing it separately,” Mercader says.
Not everyone agrees. There may have been prehistoric cultures that used heavier hammer stones and ate a wider range of nut species than we realise today, notes Sally McBrearty, a palaeoanthropologist at the University of Connecticut, Storrs. By piling inference upon inference as Mercader does, she says, “you just get on shakier and shakier ground, because of the uncertainty with each one of the steps”.
Help me, please
You may think it’s rude to blow raspberries, or grunt loudly to get someone’s attention, but chimps at the Yerkes National Primate Research Center in Atlanta, Georgia, have no such qualms. What’s more, they make these particular sounds for a specific purpose: to get the attention of a researcher when they want help in obtaining food that is out of their reach.
That insight might not seem like a big deal, but to chimp researchers it is hugely significant: it is the first time chimps have been definitively shown to use intentional vocal signals in this particular situation. In previous experiments it wasn’t clear whether the chimps were making noises just because they could see food, but now William Hopkins and colleagues at Yerkes have ruled that out by observing chimps when either alone with food, alone with a researcher, or with a researcher and food at the same time. Only in this last case did the chimps make the noises (Animal Behaviour, vol 73, p 281).
When chimps face a specific task, they fashion a tool to meet the demands of the job. “Vocal signalling is the same thing,” says Hopkins. “In this case, the tool is the human.”
This finding reopens the question of whether the ability to generate language is uniquely human. While grunts can hardly be classed as language, the chimps are in essence generating novel signals, says Hopkins. “It says mountains about their potential social cognition.”
Rowan Hooper
