Neuroplasticity enables bio-cultural feedback in Paleolithic stone-tool making.

Stone-tool making is an ancient human skill thought to have played a key role in the bio-cultural co-evolutionary feedback that produced modern brains, culture, and cognition. To test the proposed evolutionary mechanisms underpinning this hypothesis we studied stone-tool making skill learning in modern participants and examined interactions between individual neurostructural differences, plastic accommodation, and culturally transmitted behavior. We found that prior experience with other culturally transmitted craft skills increased both initial stone tool-making performance and subsequent neuroplastic training effects in a frontoparietal white matter pathway associated with action control. These effects were mediated by the effect of experience on pre-training variation in a frontotemporal pathway supporting action semantic representation. Our results show that the acquisition of one technical skill can produce structural brain changes conducive to the discovery and acquisition of additional skills, providing empirical evidence for bio-cultural feedback loops long hypothesized to link learning and adaptive change.

Emergence of perceptuomotor relationships during paleolithic stone toolmaking learning: intersections of observation and practice.

Stone toolmaking is a human motor skill which provides the earliest archeological evidence motor skill and social learning. Intentionally shaping a stone into a functional tool relies on the interaction of action observation and practice to support motor skill acquisition. The emergence of adaptive and efficient visuomotor processes during motor learning of such a novel motor skill requiring complex semantic understanding, like stone toolmaking, is not understood. Through the examination of eye movements and motor skill, the current study sought to evaluate the changes and relationship in perceptuomotor processes during motor learning and performance over 90 h of training. Participants' gaze and motor performance were assessed before, during and following training. Gaze patterns reveal a transition from initially high gaze variability during initial observation to lower gaze variability after training. Perceptual changes were strongly associated with motor performance improvements suggesting a coupling of perceptual and motor processes during motor learning.

Knowledge vs. know-how? Dissecting the foundations of stone knapping skill.

Stone tools provide some of the best remaining evidence of behavioral change over long periods, but their cognitive and evolutionary implications remain poorly understood. Here, we contribute to a growing body of experimental research on the cognitive and perceptual-motor foundations of stone toolmaking skills by using a flake prediction paradigm to assess the relative importance of technological understanding vs. accurate action execution in Late Acheulean-style handaxe production. This experiment took place as part of a larger, longitudinal study of knapping skill acquisition, allowing us to assemble a large sample of predictions across learning stages and in a comparative sample of experts. By combining group and individual-level statistical analyses with predictive modeling, we show that understanding and predicting specific flaking outcomes in this technology is both more difficult and less important than expected from previous work. Instead, our findings reveal the critical importance of perceptual motor skills needed to manage speed-accuracy trade-offs and reliably detach the large, invasive flakes that enable bifacial edging and thinning. With practice, novices increased striking accuracy, flaking success rates, and (to an extent) handaxe quality by targeting small flakes with acute platform angles. However, only experts were able to combine percussive force and accuracy to produce results comparable with actual Late Acheulean handaxes. The relatively intense demands for accurate action execution documented in our study indicate that biomechanical properties of the upper limb, cortical and cerebellar systems for sensorimotor control, and the cognitive, communicative, and affective traits supporting deliberate practice would all have been likely targets of selection acting on Late Acheulean toolmaking aptitude.

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

Before Europeans arrived to Eastern North America, prehistoric, indigenous peoples experienced a number of changes that culminated in the development of sedentary, maize agricultural lifeways of varying complexity. Inherent to these lifeways were several triggers of social stress including population nucleation and increase, intergroup conflict (warfare), and increased territoriality. Here, we examine whether this period of social stress co-varied with deadlier weaponry, specifically, the design of the most commonly found prehistoric archery component in late pre-contact North America: triangular stone arrow tips (TSAT). The examination of modern metal or carbon projectiles, arrows, and arrowheads has demonstrated that smaller arrow tips penetrate deeper into a target than do larger ones. We first experimentally confirm that this relationship applies to arrow tips made from stone hafted onto shafts made from wood. We then statistically assess a large sample (n = 742) of late pre-contact TSAT and show that these specimens are extraordinarily small. Thus, by miniaturizing their arrow tips, prehistoric people in Eastern North America optimized their projectile weaponry for maximum penetration and killing power in warfare and hunting. Finally, we verify that these functional advantages were selected across environmental and cultural boundaries. Thus, while we cannot and should not rule out stochastic, production economizing, or non-adaptive cultural processes as an explanation for TSAT, overall our results are consistent with the hypothesis that broad, socially stressful demographic changes in late pre-contact Eastern North America resulted in the miniaturization-and augmented lethality-of stone tools across the region.

Understanding stone tool-making skill acquisition: Experimental methods and evolutionary implications.

Despite its theoretical importance, the process of stone tool-making skill acquisition remains understudied and poorly understood. The challenges and costs of skill learning constitute an oft-neglected factor in the evaluation of alternative adaptive strategies and a potential source of bias in cultural transmission. Similarly, theory and data indicate that the most salient neural and cognitive demands of stone tool-making should occur during learning rather than expert performance. Unfortunately, the behavioral complexity and extensive learning requirements that make stone knapping skill acquisition an interesting object of study are the very features that make it so challenging to investigate experimentally. Here we present results from a multidisciplinary study of Late Acheulean handaxe-making skill acquisition involving twenty-six naïve participants and up to 90 hours training over several months, accompanied by a battery of psychometric, behavioral, and neuroimaging assessments. In this initial report, we derive a robust quantitative skill metric for the experimental handaxes using machine learning algorithms, reconstruct a group-level learning curve, and explore sources of individual variation in learning outcomes. Results identify particular cognitive targets of selection on the efficiency or reliability of tool-making skill acquisition, quantify learning costs, highlight the likely importance of social support, motivation, persistence, and self-control in knapping skill acquisition, and illustrate methods for reliably reconstructing ancient learning processes from archaeological evidence.

Going big versus going small: Lithic miniaturization in hominin lithic technology.

Lithic miniaturization was one of our Pleistocene ancestors' more pervasive stone tool production strategies and it marks a key difference between human and non-human tool use. Frequently equated with "microlith" production, lithic miniaturization is a more complex, variable, and evolutionarily consequential phenomenon involving small backed tools, bladelets, small retouched tools, flakes, and small cores. In this review, we evaluate lithic miniaturization's various technological and functional elements. We examine archeological assumptions about why prehistoric stoneworkers engaged in processes of lithic miniaturization by making small stone tools, small elongated tools, and small retouched and backed tools. We point to functional differences that motivate different aspects of lithic miniaturization and several instances where archeological systematics have possibly led archeologists to false negative findings about lithic miniaturization. Finally, we suggest productive avenues by which archeologists can move closer to understanding the complex evolutionary forces driving variability in lithic miniaturization.