Science Literature

The ability of chimpanzees to construct tools has long been an interest of anthropological researchers. The first and only data regarding past tool-making activity has just appeared in the PNAS. The Panin sites from West Africa are the only known prehistoric chimpanzee settlements, and these have "yielded behaviorally modified stones, dated by chronometric means to 4,300 years of age".
The press release explains the rationale for the researchers' conclusion: "The stones they excavated show the hallmarks of use as tools for smashing nuts when compared to ancient human or modern chimpanzee stone tools." In other words, the researchers have made a design inference, based on the data they have gathered. The stones bear the characteristic marks of being used as tools, and starch grains were found on the stones (an indication that the chimps were cracking nuts). It is a good example of a design inference in science, in this case involving non-human subjects. It is a much needed reminder that science should never be defined so as to exclude intelligent causation.
Some analysis of the significance of the finding has been made. The researchers say their work "suggests that percussive material culture could have been inherited from an common human-chimpanzee clade, rather than invented by hominins, or have arisen by imitation, or resulted from independent technological convergence." This does seem to be premature at best. What the data shows is behavioural stasis: chimps today can use tools to crack nuts; chimps 4300 years ago used tools to crack nuts. The data does not constrain explanations of the origins of this trait. One can interpret this in terms of Kuhnian "normal" science, whereby evidence for stasis is interpreted in terms of the prevailing evolutionary paradigm. Of the various options, the authors favour the idea that humans and chimps shared a common ancestor that possessed tool-making abilities. One suspects this hypothesis will not survive critical appraisal by peers.

4300-year-old chimpanzee sites and the origins of percussive stone technology
Mercader, Julio, Huw Barton, Jason Gillespie, Jack Harris, Steven Kuhn, Robert Tyler, and Christophe Boesch
Proceedings of the National Academy of Sciences, published February 20, 2007, 10.1073/pnas.0607909104

Abstract: Archaeological research in the African rainforest reveals unexpected results in the search for the origins of hominoid technology. The ancient Panin sites from Cote d'Ivoire constitute the only evidence of prehistoric ape behavior known to date anywhere in the world. Recent archaeological work has yielded behaviorally modified stones, dated by chronometric means to 4,300 years of age, lodging starch residue suggestive of prehistoric dietary practices by ancient chimpanzees. The "Chimpanzee Stone Age" pre-dates the advent of settled farming villages in this part of the African rainforest and suggests that percussive material culture could have been inherited from an common human-chimpanzee clade, rather than invented by hominins, or have arisen by imitation, or resulted from independent technological convergence.

See also:

The Chimpanzee Stone Age . West African chimpanzees have been cracking nuts with stone tools for thousands of years
Max Planck Society, 13 February 2007.

Ancient chimps 'used stone tools'
Chimpanzees in West Africa used stone tools to crack nuts 4,300 years ago. BBC News, BBC News, 13 February 2007.