Modeling a primate technological niche

The archaeological visibility of chimpanzee (Pan troglodytes) nut-cracking

The earliest evidence for complex tool use in the archaeological record dates to 3.3 Ma. While wooden tools may have been used by our earliest ancestors, the evidence is absent due to poor preservation. However, insights into possible early hominin wooden tool use can be gained from observing the tool-use practices of our closest living relatives, chimpanzees (Pan troglodytes). By using stone hammers used to crack various nuts, chimpanzees leave a durable material signature comprised of formal tools and associated diagnostic fragments. While the archaeological evidence of chimpanzee wooden tool use is temporary, the combination of stone hammers and wooden anvils can create a more enduring lithic record. This study explores the lithic assemblages associated with wooden and stone anvil use at nut-cracking sites in Taï National Park, Côte d'Ivoire, using technological and use-wear analyses. Our results indicate clear differences in density, fracture patterns, and use-wear in the lithic records between wooden anvil and stone anvil sites. New archaeological excavations at six chimpanzee nut-cracking sites reveal that the anvils' material directly influences the visibility of nut-cracking evidence in the archaeological record. By examining the nature of the lithic signatures associated with wooden anvil and stone anvil use by chimpanzees, we can formulate hypotheses about the probability of such behaviors being preserved and identifiable in the Plio-Pleistocene hominin archaeological record. The variability in material signatures from nut-cracking on different anvils suggests that stone anvils leave a clear archaeological record. Evidence for wooden anvil use is likely underrepresented due to the more ephemeral nature of the associated percussive damage and material signature. It may, however, still be possible, albeit challenging, to identify wooden anvil use in the archaeological record.

Searching for the earliest archaeological record: insights from chimpanzee material landscapes

The origin of tool use is a central question in human evolutionary studies. Plio-Pleistocene core and flake technologies represent the earliest evidence of tool use in the human lineage. Some suggest this form of tool use is probably pre-dated by a phase of percussive tool use. However, there is currently no evidence for such a record. The archaeological signature of solely percussive behaviours is not as well understood as that associated with cores and flakes. The durable nature of primate percussive stone tools and their by-products provide an opportunity to investigate what such a record looks like. Here, we present a landscape-scale study of the chimpanzee (Pan troglodytes verus) material culture from the Djouroutou Chimpanzee Project, Taï Forest, Cote d'Ivoire. This study explores the interplay between behavioural and environmental factors in shaping the stone record of nut cracking. Through a survey of nut-cracking sites, the available nut species, and raw materials, we show how resource availability influences the resulting material signature of nut cracking. These results also reveal the diversity of material signatures associated with a purely percussive material record. We gain insight into the range of signatures that may be associated with a pre-core and flake archaeological record, providing new expectations for an earlier record of tool use.

Primate archaeology 3.0

The new field of primate archaeology investigates the technological behavior and material record of nonhuman primates, providing valuable comparative data on our understanding of human technological evolution. Yet, paralleling hominin archaeology, the field is largely biased toward the analysis of lithic artifacts. While valuable comparative data have been gained through an examination of extant nonhuman primate tool use and its archaeological record, focusing on this one single aspect provides limited insights. It is therefore necessary to explore to what extent other non-technological activities, such as non-tool aided feeding, traveling, social behaviors or ritual displays, leave traces that could be detected in the archaeological record. Here we propose four new areas of investigation which we believe have been largely overlooked by primate archaeology and that are crucial to uncovering the full archaeological potential of the primate behavioral repertoire, including that of our own: (1) Plant technology; (2) Archaeology beyond technology; (3) Landscape archaeology; and (4) Primate cultural heritage. We discuss each theme in the context of the latest developments and challenges, as well as propose future directions. Developing a more "inclusive" primate archaeology will not only benefit the study of primate evolution in its own right but will aid conservation efforts by increasing our understanding of changes in primate-environment interactions over time.

Influence of COVID-19 on the emergence of stone-tool use behavior in a population of common long-tailed macaques (Macaca fascicularis fascicularis) in Thailand

Stone tool use is a rare behavior across nonhuman primates. Here we report the first population of common long-tailed macaques (Macaca fascicularis fascicularis) who customarily used stone tools to open rock oysters (Saccostrea forskali) on a small island along the Thai Gulf in Koh Ped (KPE), eastern Thailand. We observed this population several times during the past 10 years, but no stone-tool use behavior was observed until our survey during the coronavirus disease 2019 (COVID-19) pandemic in July 2022. KPE is located in Pattaya City, a hotspot for tourism in Thailand. Tourists in this area frequently provided large amounts of food for the monkeys on KPE. During the COVID-19 curfew, however, tourists were not allowed to access the island, and monkeys began to face food scarcity. During this time, we observed stone-tool use behavior for the first time on KPE. Based on our observations, the first tool manipulation was similar to stone throwing (a known precursor of stone tool use). From our observations in March 2023, we found 17 subadult/adult animals performing the behavior, 15 of 17 were males and mostly solitary while performing the behavior. The M. f. fascicularis subspecies was confirmed by distribution, morphological characteristics, and mtDNA and SRY gene sequences. Taken together, we proposed that the stone tool use behavior in the KPE common long-tailed macaques emerged due to the COVID-19 food scarcity. Since traveling is no longer restricted many tourists have started coming back to the island, and there is a high risk for this stone tool-use behavior to disappear within this population of long-tailed macaques.

Modeling Oldowan tool transport from a primate perspective

Living nonhuman primates have long served as a referential framework for understanding various aspects of hominin biological and cultural evolution. Comparing the cognitive, social, and ecological contexts of nonhuman primate and hominin tool use has allowed researchers to identify key adaptations relevant to the evolution of hominin behavior. Although the Oldowan is often considered to be a major evolutionary milestone, it has been argued that the Oldowan is rather an extension of behaviors already present in the ape lineage. This is based on the fact that while apes move tools through repeated, unplanned, short-distance transport bouts, they produce material patterning often associated with long-distance transport, planning, and foresight in the Oldowan. Nevertheless, remain fundamental differences in how Oldowan core and flake technology and nonhuman primate tools are used. The goal of the Oldowan hominins is to produce sharp-edged flakes, whereas nonhuman primates use stone tools primarily as percussors. Here, we present an agent-based model that investigates the explanatory power of the ape tool transport model in light of these differences. The model simulates the formation of the Oldowan record under the conditions of an accumulated short-distance transport pattern, as seen in extant chimpanzees. Our results show that while ape tool transport can account for some of the variation observed in the archaeological record, factors related to use-life duration severely limit how far an Oldowan core can be moved through repeated short-distance transport bouts. Thus, the ape tool transport has limitations in its ability to explain patterns in the Oldowan. These results provide a basis for discussing adaptive processes that would have facilitated the development of the Oldowan.

Linking primatology and archaeology: The transversality of stone percussive behaviors

Since the launch of the Journal of Human Evolution fifty years ago, the archaeology of human origins and the evolution of culture have witnessed major breakthroughs with the identification of several new archaeological sites whose chronology has been slowly pushed back until the discovery of the earliest evidence of stone tool making at Lomekwi 3 (West Turkana, Kenya), at 3.3 Ma. Parallel to these discoveries, the study of wild primates, especially chimpanzees (Pan troglodytes), allowed the development of models to understand key aspects of the behavior of extinct hominin species. Indeed, chimpanzees possess an impressive diversity of tool-aided foraging behaviors, demonstrating that technology (and culture) is not exclusive to humans. Additionally, current research has also shown that wild capuchin monkeys (Sapajus libidinosus) and long-tailed macaques (Macaca fascicularis) also rely on stone percussive foraging behaviors. The investigation of these primates is boosting new interpretative models to understand the origins of stone flaking and the archaeological signature left by these primates. This review aims to present an examination of the state-of-the-art and the current advances made in the study of the earliest hominin technology and primate percussive behaviors. Overall, we argue that while it has been shown that extant primates can generate unintentional flakes, early hominins exhibited skills in the production and use of flakes not identified in primates. Nonetheless, we stand up to continue developing interdisciplinary approaches (i.e., primate archaeology) to study extant primates, as these endeavors are essential to move forward toward a detailed understanding of the technological foraging behaviors beyond the genus Homo. Finally, we discuss future challenges for the study of the emergence of stone technology.

A primate model for the origin of flake technology

When and how human ancestors first used tools remains unknown, despite intense research into the origins of technology. It has been hypothesized that the evolutionary roots of stone flake technology has its origin in percussive behavior. Before intentional stone flaking, hominins potentially engaged in various percussive behaviors resulting in accidental flake detachments. We refer to this scenario as the 'by-product hypothesis.' In this scenario, repeated detachments of sharp stone fragments eventually resulted in intentional flake production. Here, we tested the circumstances of accidental flake production as a by-product of percussive foraging in wild capuchin monkeys (Sapajus libidinosus) from Brazil, the only nonhuman primate known to habitually produce sharp-edged flakes through a percussive behavior. We conducted field experiments where we tested the potential for accidental flake production during nut cracking. We provided three different types of stone with varied material properties as anvils to assess the circumstances in which accidental production of sharp-edged flakes occurs during nut cracking. A further freehand knapping experiment, with the raw material that exhibited accidental flake detachments, allows a direct comparison of flakes that have been intentionally produced by an experienced knapper and flakes produced during nut cracking by capuchin monkeys. Our results show that raw material quality and morphology significantly affect the rate of sharp-edged flake production as well as the resulting lithic signature of this behavior. In addition, accidental flakes produced during capuchin nut cracking on highly isotropic raw material are similar in many respects to intentionally produced flakes by a human knapper. Our field experiments highlight the fact that nut-cracking behavior can lead to the unintentional production of substantial quantities of sharp-edged flakes and therefore supports the 'by-product hypothesis' as a potential mechanism for the emergence of hominin flake technology.

Identifying functional and regional differences in chimpanzee stone tool technology

The earliest hominin archaeological sites preserve a record of stone tools used for cutting and pounding. Traditionally, sharp-edged flakes were seen as the primary means by which our earliest ancestors interacted with the world. The importance of pounding tools is increasingly apparent. In some cases, they have been compared with stone hammers and anvils used by chimpanzees for nut-cracking. However, there has been little focus on providing a robust descriptive and quantitative characterization of chimpanzee stone tools, allowing for meaningful comparisons between chimpanzee groups and with archaeological artefacts. Here we apply a primate archaeological approach to characterize the range of chimpanzee nut-cracking stone tools from Djouroutou in the Taï National Park. By combining a techno-typological analysis, and two- and three-dimensional measures of damage, we identify clear differences in the location and extent of damage between nut-cracking hammerstones and anvils used at Djouroutou and when compared with other wild chimpanzee populations. Furthermore, we discuss these results in relation to interpretations of Plio-Pleistocene percussive technology. We highlight potential difficulties in identifying the underlying function of percussive artefacts based on morphological or techno-typological attributes alone. The material record from Djouroutou represents an important new datum of chimpanzee regional and material culture.