Complex tool sets for honey extraction among chimpanzees in Loango National Park, Gabon
Introduction
Homo faber was once proposed as a label for humans in order to capture their unique aptitude for tool use, which placed them apart from all other animals (Oakley, 1956). Since then, researchers have imposed chimpanzees (Pan troglodytes) into this special category, as their tool use abilities have been shown to be universal and very flexible (e.g., Goodall, 1970, Boesch and Boesch, 1990, McGrew, 1992, Whiten et al., 1999, Sanz and Morgan, 2007). The ubiquity of chimpanzee tool use has convinced most anthropologists that chimpanzees are part of this tool user category (Ambrose, 2001). Nevertheless, new criteria have frequently been proposed to qualify the differences between the two species. The classic criterion is that only humans modify natural objects to fashion tools (Leakey, 1961): a claim that was contradicted in the early 1960's from observations of spontaneous use of sticks by the Gombe chimpanzees when fishing for termites (Goodall, 1964). Next, it was proposed that only humans possess tool kits comprised of different tool types, of which each fulfills a different function (Oakley, 1956), however, the growing list of tool types used by the chimpanzee populations in Gombe, Mahale, Taï, Bossou, and Goualougo, all of whom were observed using between 15 to 25 different types of tools, have modified this claim (Sugiyama and Koman, 1979, Boesch and Boesch, 1990, Sanz et al., 2004). Another major claim was that only humans are dependent on tools for their survival (Trinkaus, 1992), but a more complete analysis has shown that, in some chimpanzee populations, the quantity of food that was acquired with tools is very important during some periods of the year (Boesch, 1996, Yamakoshi, 1998). Another proposition was that only humans fashion tools following arbitrary cultural rules rather than in a purely adaptive way (Klein, 2000). However, population differences in tool use, such as for ant dipping, were also shown to be cultural rather than adaptive (Boesch, 1996, Moebius et al., 2008). It has been proposed that only humans use tools to access underground food (Hatley and Kappelman, 1980, Wrangham et al., 1999, Laden and Wrangham, 2005), which is thought to be indicative of some higher cognitive abilities. However, new observations have documented underground food extraction with tools in different chimpanzee populations (Lanjouw, 2002, Sanz et al., 2004, Hernandez-Aguilar et al., 2007). Additionally, it was proposed that only humans use tools to hunt (Leakey, 1961), but recent observations from Fongoli chimpanzees complemented those from Gombe and Taï and help weaken this claim (Plooij, 1978, Boesch and Boesch-Achermann, 2000, Pruetz and Bertolani, 2007). Finally, it has been suggested that humans are the only species to combine many tools to attain one goal, as well as use one tool for more than one purpose (Oakley, 1956). Only one type of tool is used in most cases of chimpanzee tool use, and tools are not often used for multiple purposes, but recently some evidence suggests that tool sets (i.e., different tool types that need to be used one after the other in order to reach one goal) might be regularly used by chimpanzees of Central Africa (Suzuki et al., 1995, Bermejo and Illero, 1999, Sanz et al., 2004). Combined, these studies suggest that much of what has been proposed as qualitative differences between these two species might instead be quantitative differences.
Because tool use is now recognized in chimpanzees, adopting an integrated framework to describe the details and technological complexities observed in chimpanzees might help us in understanding the similarities and differences between chimpanzee and human tool-using skills. In addition, the identification of qualitative differences in tool-using abilities may enable us to detect which cognitive and technical skills were likely to have been important in human evolution (McGrew, 1992, Byrne, 2004). Oswalt (1976) was one of the first to propose a single framework to describe the complexity of material culture in different human civilizations, adopting a hierarchical and dichotomous taxonomy that allowed quantitative comparisons between forms and cultures. Semenov (1964) pioneered a detailed analysis of macro- and micro-traces on stones and bones to understand their functions and the way of life for the people that employed those tools. At the same time, the “chaîne opératoire” framework was applied in archaeology to detail the dynamic interactions between the object and the technological activities (Leroi-Gourhan, 1964, Lemonnier, 1983, Bar-Yosef et al., 1992, Roche et al., 1999). Such approaches have been applied to tool use in non-human primates with the aim of making comparisons between species (McGrew, 1987, Westergaard, 1994, Pruetz and Bertolani, 2007, Carvalho et al., 2008). Tool complexity has been described in terms of technounits (Oswalt, 1976), sequences or order (Wynn and McGrew, 1998, Carvalho et al., 2008), or hierarchical organization (Byrne, 2004).
To better understand the similarities and differences in tool use behavior between humans and chimpanzees, we present evidence of tool use in a newly studied population of chimpanzees in Loango National Park, Gabon. Within this population, we have documented extensive use of tool sets of up to five different tools to extract honey from hives of different species of bees, including some with underground nests. By analyzing the complexity of this extractive technology using a chaîne opératoire or operational sequence approach, which lists all possible sequential steps required from the selection of the raw material to the fulfillment of the goal, will allow us to make comparisons with observations of tool use in other chimpanzees and with tool use in Early and Middle Stone Age hominins.
Section snippets
Study site and habituation
Loango National Park is located on the coast of Gabon, between the border with Congo and the capital city of Libreville, and was officially declared a national park in 2002. Our study site is in the southwest section of the park between the Atlantic Ocean and a large lagoon. The site consists of several vegetation types including coastal forest, swamps, dry forest, and mangroves.
The project started in February 2005 with the aim of habituating both chimpanzees and gorillas, with two teams of 2
Direct observations of tool use by chimpanzees
Habituation of chimpanzees takes five years on average, so that it is not surprising that our direct observations of tool use are limited (Goodall, 1986, Boesch and Boesch-Achermann, 2000). However, we did make some clear observations of tool use in chimpanzees for the purpose of honey extraction. On July 6th, 2005, a group of 9 chimpanzees was seen gathered around a large sweat bee nest located approximately 40 m high in a tree. J.H. and an assistant heard a heavy pounding sound and saw a large
Discussion
Tool sets, which have been proposed to be uniquely important in human tool use, have rarely been observed in wild chimpanzee populations until recently. One notable exception involved Taï chimpanzees, who were observed using hammers to break the nuts of Panda oleosa, Parinari excelsa, or Detarium senegalense, and were often seen inserting a stick in order to extract pieces of kernel from inside the shells (Boesch and Boesch, 1990). Furthermore, a reintroduced group of chimpanzees in Liberia was
Acknowledgements
We thank the Centre National des Parcs Nationaux (CNPN) and the Centre National de la Recherche Scientifique et Technique (CENAREST) of Gabon for permission to conduct our research in Loango National Park. This project is financially supported by the Société pour la Conservation et le Développement (SCD) and the Max Planck Society, and logistically supported by SCD and Wildlife Conservation Society (WCS). We are very grateful to Rombout Swanborn, Tomo Nishihara, and Edward Truter for their
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