Primates (2007) 41\:22-26 DOl 10.1007/sI0329-006-0020-3 ORIGINAL ARTICLE ] A nt fishing by w ild chim panzees is not lateralised L . F. M archant· W . C . M cG rew Received: 16 Fehruary 20061 Accepted: 29 August 2006/Puhlished online: 15 November 2006 © Japan Monkey Centre and Springer 2006 A bstract Right-dominant handedness is unique and universal in lIomo sapiens, suggesting that it is a highly derived trait. Our nearest living relations, chimpan- zees, show lateralised hand preference when using tools, but not when otherwise manipulating objects. We report the first contrary data, that is, non-latera- lised tool-use, for ant fishing as done in the Mahalc Mountains of Tanzania. Unlike nut cracking, termite fishing, and fruit pounding, as seen elsewhere, in which most individuals are either significantly or wholly left- or right-biassed, ant fishers are mostly ambilateral. The clue to this exception lies in arboreality; all other pat- terns of chimpanzee elementary technology are done on the ground. Arboreal tool use usually requires not only that one hand be used to hold the tool, but also that the other hand gives postural support. When the supporting hand is fatigued, then it must be relieved by the other. Terrestrial tool use entails no such trading off. To test the hypothesis, we compared frequency of hand changing with the incidence of major hand sup- port, and found them to be significantly positively L. F. Marchant (lBJ) . W. C. McGrew Department of Anthropology, Miami University, Oxford, OH 45056, USA e-mail: marchalf@muohio.edu W. C. McGrew Department of Zoology. Miami University. Oxford, OH 45056, USA W. C. McGrew Leverhulmc Centre for Human Evolutionary Studies, Department of Biological Anthropology, University of Camhridge, Camhridge CB2 3DZ, UK <£:} Springer correlated. The evolutionary transition from arboreal- ity to terrestriality may have been a key enabler for the origins of human laterality. K eyw ords Pan troglodytes . Tool use . Handedness . Elementary technology· Insectivory Introduction Living humans (Homo s. sapiens) show universal and unique right-hand predominance at the species level, while living apes show only individual-level hand preferences in certain contexts. More precisely, in all human cultures in which handedness has been re- corded, about 90% of individuals show overall right handedness. In contrast, at least some wild great apes (Gorilla gorilla, Pan troglodytes), typically show am- bilaterality for hand use, except in two contexts of extractive foraging: food processing (= transformation of a natural food item to a more edible state by dis- abling its mechanical defenses) (Byrne et al. 2001) and tool use (see review in McGrew and Marchant 1997). With one exception (foliage processing by mountain gorillas, Byrne and Byrne 1991), individual lateralisa- tion does not mean collective bias to one side or the other at the population level. Whether cracking nuts, fishing for termites, pounding or peeling hard-shelled fruits, most individuals in a population are significantly biased, but in about equal numbers to left or right (see Table 1). Table 1 lists all published studies of wild chimpan- zees in which individuals can be statistically tested for classification by hand preference. Table 1 lists exam- ples of object manipulation without tool use: five of the