Toshisada Nishida¹, William C. McGrew² & Linda F. Marchant^3
1 Deceased
² Div. of Biological Anthropology, Dept. of Archaeology & Anthropology, Univ. of Cambridge, UK
³ Dept. of Anthropology, Miami University (Ohio), USA

The importance of throwing has figured consistently and prominently in scenarios about the evolutionary origins of human behaviour^1,2 The utility of imparting force to airborne projectile weapons, launched ballistically, is obvious, whether to deter, punish or subdue predators, prey, or competitors. Other functions of throwing are less obvious but could be equally useful, such as bringing down hanging fruit, gaining others’ attention, shattering large objects into fragments, etc. Scenarios have stressed a number of important variables, such as posture (especially bipedality), sensorimotor skill (especially hand-eye coordination), cerebral asymmetry, etc. Calvin¹ linked all of these to the evolutionary origins of language. However, few of these ideas have been tested empirically.

One way to tackle evolutionary aspects of human throwing is to look at throwing performance in our nearest living relations. Although throwing has been known in both wild³ and captive⁴ chimpanzees for almost a century, quantitative studies are few; often they are subsumed in broader studies of manual behaviour, e.g. ref. 5. Furthermore, studies often do not distinguish between aimed (targeted) throwing versus unaimed (perhaps better termed hurling) throwing, underarm versus overarm delivery, or one-handed versus two-handed throwing.

Several studies of manual laterality in throwing by captive chimpanzees have been published, and all have reported population-level, right-sided bias^6–8. Others have incorporated these reported findings into comprehensive accounts of the origin of handedness, e.g. ref. 9

We can find no published quantitative data on manual laterality in throwing from any non-human primate species in nature, much less from chimpanzees. One obvious reason for this absence is that, unlike in the artificial conditions of captivity, wild primates throw only rarely. Here we report such a dataset, collected ethologically from a population of chimpanzees in nature, over an extended period, in an effort to balance the picture.

The subjects were the eastern chimpanzees (Pan troglodytes schweinfurthii) of M group in the Mahale Mountains of western Tanzania^10,11. This population has been studied since 1965, making it the second-oldest field study of chimpanzees; the apes are fully habituated to close-range behavioural observation. The Mahale ethogram is well-known and described; Nishida et al.¹² listed 10 kinds of throwing.

We recorded all observed occurrences of throwing, using ad lib. sampling, that is, regardless of whether behaviour was being scan-sampled or focal-subject-sampled¹³. We interrupted normal protocols, in order to note the identity of the thrower, target, etc. Nishida recorded his data from 1999–2004, when he mostly followed males, hence the shortage of data on females. McGrew and Marchant recorded their data in 1996. Here we report data only on unimanual versus bimanual data, and on the hand(s) involved. Each throw is considered an independent data-point, as the chimpanzees always repositioned themselves between throws, usually to pick up another object.

We recorded 556 throws by 16 individuals (Table 1); the median number of throws per subject was 33 (range: 9&ndash72). Of these, 63 (11%) were done two-handed, usually in agonistic charging displays; almost half of these were done by two high-ranking adult males (DE, n = 17; FN, n = 13). These appeared to be unaimed and perforce were done bipedally; they are considered no further here.

One-handed throwing was unlateralized. Only 4 (BB, CT, IV, OR) of the 16 individuals showed statistically significant (Binomial test, two-tailed, p < 0.05) laterality; three were biased to the right versus one to the left The remaining 12 subjects showed ambilateral performance. Overall, nine individuals showed (non-significantly) more right-sided throws, six showed left-sided throws (a non-significant difference, n = 15, x = 6, p = 0.60), and one was tied. Descriptively overall, of one-handed throws, 226 (46%) were done with the left hand versus 267 (54%) with the right hand.

These results clearly contrast with those from the most thorough study done in captivity: Hopkins et al.⁷ found that of 89 subjects with six or more data-points, 50 were right-biased, 23 were left-biased, and 16 were unbiased. We have no explanation of this remarkable difference, although it joins a long list of behavioural contrasts between nature and captivity, in which captive chimpanzees are lateralised, while wild chimpanzees are not (see summary in ref. 14). We can find no reports of two-handed throwing by captive chimpanzees; whether this is because such behaviour was not reported, or because it is absent, remains to be seen.

Earlier, McGrew and Marchant¹⁵ hypothesised that captive chimpanzees might be biased toward right-sidedness by their lengthy (sometimes lifetime) association with human caretakers, most of whom will have been right-handed. However, a recent extensive study of four great ape species (see below) found species-level right-sided laterality in captive chimpanzees, at least based on a single bimanual measure¹⁶.

The implications for the evolutionary origins of human handedness are no clearer than the present state of play of contradictory studies of behavioural laterality. Handedness in living Homo sapiens could be a derived trait (of uncertain time-depth) or a primitive trait that could date back as far as the last common ancestor of the present African apes and humans (perhaps as long ago as 6–7 million years). Results on manual laterality for the only living Asian great ape, the orang-utan, Pongo pygmaeus, are confusing, as according to Hopkins et al.¹⁶, they are a left-handed species.

What is clear is that chimpanzees both in captivity and in nature habitually throw, despite being non-linguistic quadrupeds. Thus it is not necessary to invoke bipedal stance or co-evolved language to explain the evolutionary origins of throwing in the hominin lineage, and if the results from nature are to be believed, neither is it necessary to link throwing to manual lateralisation.

We thank: the Tanzania Commission for Science and Technology (COSTECH/UTAFITI), Serengeti (now Tanzania) Wildlife Research Institute (SWRI/TAWIRI), Tanzania National Parks (TANAPA) for authorisation to do the research; H.M. Nguli, E.T. Massawe, B.C. Mwasaga, and J.V. Wakibara for special administrative assistance; M. Huffman, K. Kawanaka, M. Nakamura, and S. Uehara for field collaboration; Philip and Elaina Hampton Fund (Miami University) for financial assistance to LFM & WCM, and Japanese MEXT #12375003, #16255007 for financial assistance to TN. Toshisada Nishida died on 7 June, 2011 and is much missed.

1. Calvin WH 1983. The Throwing Madonna: Essays on the Brain. McGraw-Hill, New York.
2. Isaac B 1987. Throwing and human evolution. Afr Archaeol Rev 5:3–17.
3. Goodall J 1964. Tool-using and aimed throwing in a community of free-living chimpanzees. Nature 201:1264–1266.
4. Köhler W 1927. The Mentality of Apes. 2nd edit. Kegan Paul, Trench, Trubner, London.
5. Marchant LF 1983. Hand Preferences among Captive Island Groups of Chimpanzees. PhD dissertation, Rutgers, The State University of New Jersey, New Brunswick, NJ.
6. Hopkins WD, Bard KA, Jones A, Bales SA 1993. Chimpanzee hand preference in throwing and infant cradling: Implications for the origin of human handedness. Curr Anthropol 34:786–790.
7. Hopkins WD, Russell JL, Cantalupo C, Freeman H, Schapiro SJ 2005. Factors influencing the prevalence and handedness for throwing in captive chimpanzees (Pan troglodytes). J Comp Psychol 119:363–370.
8. Hopkins WD, Russell JL, Schaeffer JA 2012. The neural and cognitive correlates of aimed throwing in chimpanzees: A magnetic resonance image and behavioural study on a unique form of social tool use. Phil Trans Roy Soc B 367:37–47.
9. Forrester GS, Quaresmini C, Leavens DA, Mareschal D, Thomas MSC 2013. Human handedness: An inherited evolutionary trait. Behav Brain Res 237:200–206.
10. Nishida T (ed.) 1990. The Chimpanzees of the Mahale Mountains. Sexual and Life History Strategies. University of Tokyo Press, Tokyo.
11. Nishida T 2012. Chimpanzees of the Lakeshore. Natural History and Culture at Mahale. Cambridge University Press, Cambridge.
12. Nishida T, Zamma K, Matsusaka T, Inaba A, McGrew WC 2010. Chimpanzee Behavior in the Wild: An Audio-visual Encyclopedia. Springer, Tokyo.
13. Martin P, Bateson P 2007. Measuring Behaviour. An Introductory Guide. 3rd edit. Cambridge University Press, Cambridge.
14. McGrew, WC, Marchant, LF 1997. On the other hand: Current issues in and meta-analysis of the behavioral laterality of hand function in nonhuman primates. Yearb Phys Anthropol 40:201–232.
15. McGrew WC, Marchant LF 2001. Ethological study of manual laterality in the chimpanzees of the Mahale Mountains, Tanzania. Behaviour 138:329–358.
16. Hopkins WD, Phillips KA, Bania A, Calcutt SE, Gardner M, Russell J, Schaeffer J, Lonsdorf EV, Ross SR, Schapiro SJ 2011. Hand preferences for coordinated bimanual actions in 777 great apes: Implications for the evolution of handedness in Hominins. J Hum Evol 60:605–611.