Miniaturization optimized weapon killing power during the social stress of late pre-contact North America (AD 600-1600)

Assessing geometric microliths as cultural markers through an analysis of shape variation and projectile performance

European geometric microlith shape variation is often used as a marker of cultural differences between groups of Mesolithic hunter gatherers and/or Neolithic farmers. Indeed, the 2D plan-view shape of these lithics is known to vary in spatially and temporally systematic ways between archaeological sites. Such differences are well evidenced in the Iberian Peninsula between the 9th and 8th millennia BP. Here we test an alternative hypothesis for the structured variation observed in geometric microliths: whether their plan-view shape significantly impacts the force, energy and displacement experienced when they are used as projectile tips. If functional differences between groups help to explain the shape variation observed in the archaeological record, then any role for cultural (non-functional social) explanations is potentially reduced. We undertook controlled static penetration tests using an Instron materials tester and an assemblage of replicated Iberian geometric microliths hafted to standardised wooden shafts. Results indicate that the maximum force required, energy used, and displacement at maximum force experienced by these hafted geometric microliths when used as projectile armatures is not significantly influenced by their 2D plan-view shape. Rather, gross form attributes such as maximum thickness, distance from the tip of the microlith to the start of the shaft, and the maximum width of the hafting substrate/adhesive are the greatest determinants of penetration ease, along with the positioning of the microlith when hafted. Our data therefore supports past research that proposes a cultural role for geometric microlithic shape variation in the European Mesolithic and Early Neolithic. Moreover, it highlights the functional importance of maintaining relatively thin microblades during microlith production, along with taking care to minimise the size of hafting components and the necessity to haft them in the most efficient way.

Aboriginal Australian weapons and human efficiency

Aggression-and its role in human societal development-continues to be hotly debated within both the sciences and the humanities. Whatever the evolutionary origins and repercussions of interpersonal and intergroup conflict for the human story, cultures around the globe have invested significant time and effort into designing deadly hand-held weaponry. Here, we describe for the first time, how humans deliver a deadly strike using two iconic and widespread Aboriginal Australian weapons: the kodj and the leangle with parrying shield. We present the world's first evaluation of striking biomechanics and human and weapon efficiency regarding this class of implement. Results demonstrate the leangle is far more effective at delivering devastating blows to the human body, while the kodj-a multi-functional tool-is more efficient for a human to manoeuvre and still capable of delivering severe blows that can cause death. Together, these data provide the beginnings of an in-depth understanding of how hand-held weaponry has impacted the human body throughout the deep past.

Tip cross-sectional geometry predicts the penetration depth of stone-tipped projectiles

Understanding prehistoric projectile weaponry performance is fundamental to unraveling past humans' survival and the evolution of technology. One important debate involves how deeply stone-tipped projectiles penetrate a target. Theoretically, all things being equal, projectiles with smaller tip cross-sectional geometries should penetrate deeper into a target than projectiles with larger tip cross-sectional geometries. Yet, previous experiments have both supported and questioned this theoretical premise. Here, under controlled conditions, we experimentally examine fourteen types of stone-tipped projectile each possessing a different cross-sectional geometry. Our results show that both tip cross-sectional area (TCSA) and tip cross-sectional perimeter (TCSP) exhibit a strong, significant inverse relationship with target penetration depth, although TCSP's relationship is stronger. We discuss why our experimental results support what is mathematically predicted while previous experiments have not. Our results are consistent with the hypothesis that when stone tip cross-sectional geometries become smaller over time in particular contexts, this evolution may be due to the selection of these attributes for increased penetration.