External ballistics of Pleistocene hand-thrown spears: experimental performance data and implications for human evolution

www.nature.com/scientificreports OPEN Received: 5 July 2018 Accepted: 15 December 2018 Published: xx xx xxxx External ballistics of Pleistocene hand-thrown spears: experimental performance data and implications for human evolution Annemieke Milks 1 , David Parker2 & Matt Pope1 The appearance of weaponry - technology designed to kill - is a critical but poorly established threshold in human evolution. It is an important behavioural marker representing evolutionary changes in ecology, cognition, language and social behaviours. While the earliest weapons are often considered to be hand-held and consequently short-ranged, the subsequent appearance of distance weapons is a crucial development. Projectiles are seen as an improvement over contact weapons, and are considered by some to have originated only with our own species in the Middle Stone Age and Upper Palaeolithic. Despite the importance of distance weapons in the emergence of full behavioral modernity, systematic experimentation using trained throwers to evaluate the ballistics of thrown spears during flight and at impact is lacking. This paper addresses this by presenting results from a trial of trained javelin athletes, providing new estimates for key performance parameters. Overlaps in distances and impact energies between hand-thrown spears and spearthrowers are evidenced, and skill emerges as a significant factor in successful use. The results show that distance hunting was likely within the repertoire of hunting strategies of Neanderthals, and the resulting behavioural flexibility closely mirrors that of our own species. The use of hand-thrown spears emerged some time during the Pleistocene, and is thought to have been an important step in human evolution, functioning not only as a precursor to mechanically-projected weaponry, but also as a weapon used for hunting and interpersonal violence until the ethnographic present. In general early weaponry is used as a proxy for a wide range of behaviours including hunting and scavenging1–5, self-defence against dangerous animals6, human-human violence7, social behaviours and group size in relation to cooperative hunting8–10, the development and use of language and teaching10,11, cognitive abilities necessary for selection of raw materials, design, and use12–16, and human dispersal events and species replacement7,17. According to models of early weaponry, hand-thrown spears chronologically follow the development of thrusting spears, but precede the development of mechanically-aided ‘complex’ projectiles such as spearthrowers and bow/arrows, which are sometimes called ‘true’ projectiles17–21. Similarly, it is argued that the ability to ‘kill at a distance’ is not present until the advent of complex projectiles17,22,23. Although hand-thrown spears have an important role in human evolution, their performance and effectiveness as hunting weapons remains poorly understood. According to multiple sources17,21,22,24–31 Pleistocene hand-thrown spears have numerous disadvantages in relation to subsequent innovations. Characterisations include that they are heavy, which makes them difficult to throw and achieve high release velocities, with further loss of velocity in flight; that they are less lethal than complex projectiles due to lower levels of kinetic energy (KE) at impact; that there are limitations on the distance from which they can be deployed compared with complex projectiles, and are inaccurate, which in turn increases danger and discoverability; and therefore there are limitations on hunting strategies and prey for hominins using hand-thrown spears. Many of these theories are based on selective or unquantified data, resulting in a lack of clarity about which aspects were likely to be true limitations4. Spear throwing experiments typically involve the use of inexperienced throwers and/or replicas designed for other delivery systems25,32,33. Data from studies involving experienced throwers typically relates to studies launching lighter objects such as throwing sticks which have different ballistic properties34. 1 Institute of Archaeology, University College London, 31-34 Gordon Square, London, WC1H, OPY, UK. 2Nordic Sport (UK) Limited, 21 Bentley Road, Castle Donington, Derby, DE74 2UL, UK. Correspondence and requests for materials should be addressed to A.M. (email: ) Scientific Reports | (2019) 9:820 | https://doi.org/10.1038/s41598-018-37904-w 1 www.nature.com/scientificreports/ Evidence-based debates around the origins of thrusting and throwing spear use in human evolution have typically focused on hominin skeletal evidence. Proposals that features of the upper limbs of different species of Homo indicate that throwing only comes into play with H. sapiens23,35 are hampered by multiple issues. These include small sample sizes, human variation in populations36, evidence that humeral robusticity and shape may not correlate with strains in weapon use37, and a lack of clarity whether any single activity contributes to or offsets bone remodeling or robusticity36,38,39. Others argue for an earlier emergence of throwing, showing that features necessary for accurate and powerful throwing are evidenced in H. erectus fossils40–42. A recent find of an early Neanderthal dating to MIS 7 from Tourville-la-Rivière shows skeletal trauma consistent with repeated throwing, supporting the hypothesis that they were capable and frequent throwers43. Archaeology can and should make a valuable contribution to the debate on spear throwing but thus far systematic research into the ballistics of early spears as thrown weapons has lagged behind both palaeoanthropological research and archaeological approaches to complex projectiles, although such research is beginning to be undertaken33,44. The earliest spear is a fragment that dates to ca. 400,000 BP from Clacton-on-Sea (UK), and was crafted out of yew1,45. The site of Schöningen (Germany) dates to ca. 300,000 BP and has yielded at least 10 complete and nearly complete wooden spears, most of which are made of slow-growing spruce46,47. Most of the wooden spears from Schöningen are tapered at both ends47 and of those whose maximum diameter locations have been published, the widest diameters are located in the front half46 suggesting that the hominins manufacturing them may have intentionally designed at least some of the spears as flight weapons for hunting (See Supplementary Information regarding design requirements for flight). Evaluating the ballistics of thrown spears is valuable not only for the analysis of specific archaeological sites and artefacts, but also for broad chrono-geographical comparisons of hunting behaviours throughout the Eurasian Palaeolithic, African Stone Age, Australian archaeological contexts, and Paleoindian archaeological record, all of which have suitable if rare examples of fragments or complete one-piece untipped pointed artefacts interpreted as spears45–52, as well as lithic and osseous points proposed (...truncated)