December 28, 2011

The function of the Aterian

From the paper:
The ability of human hunters to ‘kill at a distance’ [1], [2] is often considered one of the hallmarks of modern human behavior. Such an ability embodies the cultural transcendence of the human body's condition with the aid of technology and has deep implications for the self-understanding of our species's uniqueness in the animal kingdom. For this reason, the search for evidence of projectile weapon technologies in the Stone Age has superseded the search for evidence of mere hunting activities, the latter having slid in the background of pre-human hominin behavioral repertoire [3]–[5]. Because ‘safe hunting’ is considered to have given anatomically-modern humans a competitive advantage against Neandertals during the last Out-of-Africa event (e.g., [6], [7]), it is extremely important to rigorously examine claims for the existence of such technologies, even when the superficial examination of the morphology of a particular tool suggests a clear functional determination. Such is the case of the Aterian tanged (or stemmed) point, a type of stone tool found throughout North Africa in a variety of ecological, geographical, and chronological contexts within the African Middle Stone Age (MSA), and which exhibits a simple form that is sometimes reminiscent of stemmed arrowheads or spear points from much later time periods (Figure 1). ... The importance of correctly interpreting the function of Aterian stemmed tools is underlined by recent dating results, which suggests that, contrary to early assumptions, it could date to as early as MIS 5 and before [29]. More specifically, new dates from a series of sites, such Mugharet el-Aliya [30], Rhafas [31], Ifri n'Ammar [29], Dar-es-Soltan [32], and Contrebandiers [33] have demonstrated that tanged tools can be found in the earliest part of the North African Middle Stone Age, making them potentially the earliest evidence of prehistoric stone-tipped weaponry. However, the precise way in which they actually fit within a prehistoric technological system, including whether or not they were part of flying projectile armatures or thrusting spears, has never been rigorously determined, despite the crucial role that both projectiles and hafting are thought to play in the evolution of human cultural adaptations.
Several lines of evidence point in the direction of progressive resharpening of Aterian tools in the same manner as edge-tools such as scrapers and cutting-tools. This does not per se rule out an initial use for some Aterian pieces as weapon tips, because the ultimate use of each individual tool must be determined by the examination of use-traces, and because each episode of retouch likely wipes out previous uses of the tool. However, the data presented here make a strong case for the claim that, in general, these tools were probably hafted and used repeatedly for tasks that resulted in the need to rejuvenate edges rather than point-tips. The comparison between excavated, mostly cave contexts, and surface sites reveals that they both contain similar reduction trajectories and shape variabilities of tanged tools. This indicates that the functional emphasis on the tools was similar during their use-life in the landscape and at the repeated-occupation sites, which contradicts the expectations of breakage and repair patterns associated with a use as projectile tips [62], [63].
It is thus possible that hafting was practiced on both sides of the Mediterranean Sea, but in different ways. Although some of the differences in technological innovation between archaic and modern humans that we observe at the continental and species level may be due to cognitive differences or to demographic factors influencing the spread and accumulation of information [79], [80], we must not forget the essentially functional character of toolkits. Especially when comparing and evaluating technologies at very large scales, functional responses to specific technological problems (such as prey size and behavior [1] or increased risk associated with prey frequency and ease of hunting (e.g., [81]–[84])) may trump other factors. Even if the ultimate cause underpinning technological change is a large-scale environmental phenomenon, such as a rapid cooling event, or the aridity of a newly-colonized area, we can understand these associated changes only by unraveling the constraints imposed on toolkits by the subjects of the actions for which the tools themselves were used. Thus, perhaps the better question to answer regarding the Aterian might not be if it represents the earliest hunting weapons technology, but rather, in what way it arose out of new challenges posed by the environments that characterized North Africa since MIS 5, and how it adapted during the almost 100 thousand years of occupation of this region.
PLoS ONE 6(12): e29029. doi:10.1371/journal.pone.0029029

Shape Variation in Aterian Tanged Tools and the Origins of Projectile Technology: A Morphometric Perspective on Stone Tool Function

Radu Iovita


Recent findings suggest that the North African Middle Stone Age technocomplex known as the Aterian is both much older than previously assumed, and certainly associated with fossils exhibiting anatomically modern human morphology and behavior. The Aterian is defined by the presence of ‘tanged’ or ‘stemmed’ tools, which have been widely assumed to be among the earliest projectile weapon tips. The present study systematically investigates morphological variation in a large sample of Aterian tools to test the hypothesis that these tools were hafted and/or used as projectile weapons.

Methodology/Principal Findings Both classical morphometrics and Elliptical Fourier Analysis of tool outlines are used to show that the shape variation in the sample exhibits size-dependent patterns consistent with a reduction of the tools from the tip down, with the tang remaining intact. Additionally, the process of reduction led to increasing side-to-side asymmetries as the tools got smaller. Finally, a comparison of shape-change trajectories between Aterian tools and Late Paleolithic arrowheads from the North German site of Stellmoor reveal significant differences in terms of the amount and location of the variation.

Conclusions/Significance The patterns of size-dependent shape variation strongly support the functional hypothesis of Aterian tools as hafted knives or scrapers with alternating active edges, rather than as weapon tips. Nevertheless, the same morphological patterns are interpreted as one of the earliest evidences for a hafting modification, and for the successful combination of different raw materials (haft and stone tip) into one implement, in itself an important achievement in the evolution of hominin technologies.


1 comment:

eurologist said...

From a physics viewpoint, the shafts are too short to take a load other than predominantly longitudinal. I can't think of a paleolithic hafting technique that would have allowed any substantial perpendicular moment - the shaft simply is too short for that. So, unless one side of the "triangle" was pretty much fully covered with wood, hafted, these would have been useless as cutting tools.

One possibility how these objects may have experienced predominantly one-sided wear is as a throwing stick with a point. So, instead of being thrown like a dart or spear, they may have been thrown by gripping the end of the wooden shaft and whirling the projectile like an axe (a primitive atlatl, where the wrist provides additional momentum, but the shaft remains at the object thrown). In that case, the main load on the shaft would have been longitudinal and pulling, and when striking the target, more often than not only one cutting edge would have been involved.

This would be very useful against antelopes, who are known to exhaust quickly, and who after being struck from a distance could have been followed using blood loss traces (either by humans alone or with the aid of dogs).