Atlatl use equalizes female and male projectile weapon velocity

www.nature.com/scientificreports OPEN Atlatl use equalizes female and male projectile weapon velocity Michelle R. Bebber 1*, Briggs Buchanan 2, Metin I. Eren 1,3, Robert S. Walker 4 & Dexter Zirkle 1 The atlatl is a handheld, rod-shaped device that employs leverage to launch a dart, and represents a major human technological innovation. One hypothesis for forager atlatl adoption over its presumed predecessor, the thrown javelin, is that a diverse array of people could achieve equal performance results, thereby facilitating inclusive participation of more people in hunting activities. We tested this hypothesis via a systematic assessment of 2160 weapon launch events by 108 people who used both technologies. Our results show that, unlike the javelin, the atlatl equalizes the velocity of female- and male-launched projectiles. This result indicates that a javelin to atlatl transition would have promoted a unification, rather than division, of labor. Moreover, our results suggest that female and male interments with atlatl weaponry should be interpreted similarly. The invention of projectile hunting technology provided several advantages to past h umans1–5. Relative to thrusting a handheld spear directly into a target, hunting with projectile weaponry increases the distance between human predator and animal prey. This gap would have reduced the chance of hunter injury, increased hunter concealment, and potentially increased weapon e ffectiveness6,7. Among the first projectile hunting weapons were thrown wooden javelins, some likely tipped with stone p oints3,5,9–12. After javelins, past humans developed mechanically assisted projectile delivery systems, such as the atlatl and dart and the bow and arrow. The atlatl and dart is often assumed to be the first of these systems; a reasonable and parsimonious assumption given its production simplicity relative to the bow and arrow1,13,14. The atlatl is a straightforward yet sophisticated weapon delivery system consisting of a handheld, rod-shaped device which is used to propel a lightweight spear, referred to as a dart. Atlatls are made of wood, bone, antler, or a combination of these materials. They possess a handle on one end and a hook or indentation on the opposite end, which functions to engage the tail end of the dart. Yet in some regions a transition from the javelin directly to the bow and arrow likely occurred15–19. Additionally, simultaneous use of different weapons has been documented ethnographically as well as suggested for some Paleolithic or forager s ocieties14,20–23. The lack of consistent javelin, atlatl, dart, bow, and arrow preservation in the Pleistocene archaeological record impedes a clear understanding of technological trajectories in most geotemporal contexts8,14,24–26. Regardless of archaeological obfuscation, it is reasonable to presume that transitions from thrown javelin to atlatl and dart occurred in at least some specific contexts during the human past. Achieving a better understanding of why that transition occurred is our focus here. A transition from the thrown javelin to the atlatl-launched dart would have potentially involved tradeoffs in performance attributes and would have depended on ecology and prey characteristics, as well as economic, demographic, and cultural f actors15,27,28. Launching a dart via an atlatl essentially employs a class 1 lever: force is applied by hand to the short arm of the lever, moving the dart at the long arm of the lever, with the wrist as a fulcrum in between8. Light-weight darts launched via an atlatl can thus, on average, achieve much faster speeds and farther distances than heavier, hand-thrown javelins1,6,13,14,29. Yet, recent controlled experiments suggest that despite a dart’s increase in velocity, a javelin’s heavier mass still results in a relatively larger kinetic e nergy24, which may in certain contexts have led to greater hunting s uccess7. Additionally, while javelin use may have in some instances required closer proximity to prey, it may not have necessitated increased danger. For example, a person could throw javelins from t rees7 or use them in environments with heavy vegetation which could increase concealment25. 1 Department of Anthropology, Kent State University, Kent, OH 44242, USA. 2Department of Anthropology, University of Tulsa, Tulsa, OK 74104, USA. 3Department of Archaeology, Cleveland Museum of Natural History, Cleveland, OH 44106, USA. 4Department of Anthropology, University of Missouri, Columbia, MO 65211, USA. *email: Scientific Reports | (2023) 13:13349 | https://doi.org/10.1038/s41598-023-40451-8 1 Vol.:(0123456789) www.nature.com/scientificreports/ One proposed hypothesis for the adoption of the atlatl and dart over the thrown javelin is that the former acted as an “equalizer”, thereby facilitating the participation of more people in a hunt, and reducing social disparity27,30,31. Researchers have proposed that the effective use of javelins would have required strength, a potentially larger body size, and high investment in t raining23,32. If the atlatl and dart render body size, strength, or training time less important to hunting success, then more, or different, people could partake in the hunt which would allow a greater number of tactical options, increase the chances of hitting the animal target, and reduce the onus of hunting success on a small number of individuals possessing a particular set of physical attributes. If the atlatl was an equalizer, then there is a clear, testable prediction to support that hypothesis: in a large group of people using both a thrown javelin and the atlatl and dart, a segment of that group should see a disproportionate increase in performance in their atlatl and dart use relative to their javelin use such that any differences are eliminated. In other words, a new technology cannot be deemed an “equalizer” unless there is a documented inequality in the previous technology. Here, we test that prediction via a systematic assessment of 108 people who used both technologies. Our measured performance attribute was velocity. We predicted that if the atlatl acts as an equalizer, then a segment of our tested population who achieved relatively poor javelin velocities would exhibit a disproportionate increase in their atlatl-launched dart velocities and thus match the rest of the population. Results We compared the mean velocity between hand thrown javelins and atlatl launched darts (see Supplementary Materials). There is a strong correlation (r2 = 0.74) between individual javelin and dart velocities (see Supplementary Fig. S1). Mean dart velocity (x̅ = 16.2 m/s) is 65% faster than mean javelin velocity (x̅ = 9.8 m/s). This result is consistent with previous work on these weapon delivery s ystems23,24,33. A box plot of javelin and dart velocity by sex shows that without conditioning on grip strength female javelin velocity is significantly less than male javelin velocity (the not reported cate (...truncated)