Shared Brain Lateralization Patterns in Language and Acheulean Stone Tool Production: A Functional Transcranial Doppler Ultrasound Study

Background

The popular theory that complex tool-making and language co-evolved in the human lineage rests on the hypothesis that both skills share underlying brain processes and systems. However, language and stone tool-making have so far only been studied separately using a range of neuroimaging techniques and diverse paradigms.

Methodology/Principal Findings

We present the first-ever study of brain activation that directly compares active Acheulean tool-making and language. Using functional transcranial Doppler ultrasonography (fTCD), we measured brain blood flow lateralization patterns (hemodynamics) in subjects who performed two tasks designed to isolate the planning component of Acheulean stone tool-making and cued word generation as a language task. We show highly correlated hemodynamics in the initial 10 seconds of task execution.

Conclusions/Significance

Stone tool-making and cued word generation cause common cerebral blood flow lateralization signatures in our participants. This is consistent with a shared neural substrate for prehistoric stone tool-making and language, and is compatible with language evolution theories that posit a co-evolution of language and manual praxis. In turn, our results support the hypothesis that aspects of language might have emerged as early as 1.75 million years ago, with the start of Acheulean technology.     

EMG study of hand muscle recruitment during hard hammer percussion manufacture of Oldowan tools

The activity of 17 hand muscles was monitored by electromyography (EMG) in three subjects during hard hammer percussion manufacture of Oldowan tools. Two of the subjects were archaeologists experienced in the replication of prehistoric stone tools. Simultaneous videotapes recorded grips associated with the muscle activities. The purpose of the study was to identify the muscles most likely to have been strongly and repeatedly recruited by early hominids during stone tool-making. This information is fundamental to the identification of skeletal features that may reliably predict tool-making capabilities in early hominids. The muscles most frequently recruited at high force levels for strong precision pinch grips required to control the hammerstone and core are the intrinsic muscles of the fifth finger and the thumb/index finger regions. A productive search for skeletal evidence of habitual Oldowan tool-making behavior will therefore be in the regions of the hand stressed by these intrinsic muscles and in the joint configurations affecting the relative lengths of their moment arms. Am J Phys Anthropol 105:315–332, 1998. © 1998 Wiley-Liss, Inc.     

Morphological affinities of the Australopithecus afarensis hand on the basis of manual proportions and relative thumb length

The hands of apes and humans differ considerably with regard to proportions between several bones. Of critical significance is the long thumb relative to other fingers, which is the basis for human-like pad-to-pad precision grip capability, and has been considered by some as evidence of tool-making. The nature and timing of the evolutionary transition from ape-like to human-like manual proportions, however, have remained unclear as a result of the lack of appropriate fossil material. In this article, the manual proportions of Australopithecus afarensis from locality AL 333/333w (Hadar, Ethiopia) are investigated by means of bivariate and multivariate morphometric analyses, in order to test the hypothesis that human-like proportions, including an enhanced thumb/hand relationship, originally evolved as an adaptation to stone tool-making. Although some evidence for human-like manual proportions had been previously proposed for this taxon, conclusive evidence was lacking. Our results indicate that A. afarensis possessed overall manual proportions, including an increased thumb/hand relationship that, contrary to previous reports, is fully human and would have permitted pad-to-pad human-like precision grip capability. We show that these human-like proportions in A. afarensis mainly result from hand shortening, as in modern humans, and that these conclusions are robust enough as to be non-dependent on whether the bones belong to a single individual or not. Since A. afarensis predates the appearance of stone tools in the archeological record, the above-mentioned conclusions permit a confident refutation of the null hypothesis that human-like manual proportions are an adaptation to stone tool-making, and thus alternative explanations must be therefore sought. One hypothesis would consider manipulative behaviors (including tool-use and/or non-lithic tool-making) in early hominines exceeding those reported among extant non-human primates. Alternatively, on the basis of the many adaptations to committed bipedalism in A. afarensis, we propose the hypothesis that once arboreal behaviors became adaptively insignificant and forelimb-dominated locomotor selection pressures were relaxed with the adoption of terrestrial bipedalism, human-like manual proportions could have merely evolved as a result of the complex manipulation selection pressures already present in extant non-human primates.Both hypotheses are not mutually exclusive, and even other factors such as pleiotropy cannot be currently discarded.     

Paleopediatrics: Or when did human infants really become human?

Modern human children take about twice as long as their closest biological relative, the chimpanzee, to mature. One standard explanation for the evolution of “delayed maturation” at an early stage of human evolution is that it provided the time necessary for immature individuals to learn complex skills, most notably those relating to tool-making abilities. However, after comparing dental maturational profiles of early hominids from South Africa (who apparently did make and use stone tools) (Susman [1994] Science 265:1570–1573) to those of extant humans and chimpanzees, we find no evidence to document an association between “delayed maturation” and tool-making abilities in the early stages of human evolution. This also suggests that the assumed association between prolonged childhood dependency and other behaviors often associated with the advent of tool-making such as cooperative hunting, food sharing, home bases, sexual division of labor, etc., is also suspect. Instead, we must look for other, or additional, selective pressures for the evolution of “delayed maturation,” which may postdate the australopithecine radiation. © 1995 Wiley-Liss, Inc.     

STONE TOOLS AND THE UNIQUENESS OF HUMAN CULTURE

There is growing evidence that some species other than the human have behaviour that should be called cultural. Questions arise, then, of how human (and, perhaps, ape) cultures are different from those of other animals and how they have become so different. Human cultures are creative, generating new patterns of behaviour from those learned from others. Stone tool making provided a niche for the recruitment of tools and tool-making processes from one function to another. This is something not yet recorded for apes. This article explores the possible role of stone tools in the emergence of this creativity.     

Human-like, population-level specialization in the manufacture of pandanus tools by New Caledonian crows Corvus moneduloides

The main way of gaining insight into the behaviour and neurological faculties of our early ancestors is to study artefactual evidence for the making and use of tools, but this places severe constraints on what knowledge can be obtained. New Caledonian crows, however, offer a potential analogous model system for learning about these difficult-to-establish aspects of prehistoric humans. I found new evidence of human-like specialization in crows' manufacture of hook tools from pandanus leaves: functional lateralization or 'handedness' and the shaping of these tools to a rule system. These population-level features are unprecedented in the tool behaviour of free-living non-humans and provide the first demonstration that a population bias for handedness in tool-making and the shaping of tools to rule systems are not concomitant with symbolic thought and language. It is unknown how crows obtain their tool behaviour. Nevertheless, at the least they can be studied in order to learn about the neuropsychology associated with early specialized and/or advanced population features in tool-making such as hook use, handedness and the shaping of tools to rule systems.     

Origin of the Genus <Emphasis Type="Italic">Homo</Emphasis>

The origin of the genus Homo in Africa signals the beginning of the shift from increasingly bipedal apes to primitive, large-brained, stone tool-making, meat-eaters that traveled far and wide. This early part of the human genus is represented by three species: Homo habilis, Homo rudolfensis, and Homo erectus. H. habilis is known for retaining primitive features that link it to australopiths and for being the first stone tool makers. Little is known about H. rudolfensis except that it had a relatively large brain and large teeth compared to H. habilis and that it overlapped in time and space with other early Homo. Our understanding of the paleobiology and evolution of the larger-brained H. erectus is enhanced due to its rich fossil record. H. erectus was the first obligate, fully committed biped, and with a body adapted for modern striding locomotion, it was also the first in the human lineage to disperse outside of Africa. The early members of the genus Homo are the first to tip the scale from the more apish side of our evolutionary history toward the more human one.     

制作工具在人类演化中的地位与作用

制作工具曾经被视作人类独有的行为能力,"人类"曾经据此而定义。但目前学术界将直立行走作为人类区别于其他灵长类最重要的体质与行为特征。少量其他动物种类,尤其是非人高等灵长类,也能使用工具乃至简单制作工具。如何认识制作工具在人类演化中的作用?人类制作工具的能力与其他动物有何区别?考古学是否有能力分辨人类的工具和其他灵长类的产品?本文通过对现代巴西猴群敲砸石头的行为及其产品、4300年前黑猩猩的"石制品"和早期人类石制品的比较研究,指出人类的工具与其他动物制作和使用的工具存在根本的区别;工具制作和使用对确定人类的演化方向,增强人类的适应生存能力,塑造人类的大脑与心智及行为方式,提升语言和交流能力,形成现代人类的身心和社会,至关重要,不可或缺。考古工作者一方面需要谨慎分辨、研究人类工具制作初期的产品,不使其与自然的产物和其他动作的作品相混淆,另一方面应该认识到人类工具制作在计划性、目的性、预见性、规范性和精美度上具有唯一性,有内在的智能控制、思维逻辑和规律可循。学科发展的积累和现代科技的支撑使考古学者具有多方面的利器,能够把人类工具制作的历史挖掘、复原出来,能够破译特定的石器技术和功能,进而将人类演化的历史画卷描绘得更加精细,更加完整。     

Distribution of potential suitable hammers and transport of hammer tools and nuts by wild capuchin monkeys

Selection and transport of objects to use as tools at a distant site are considered to reflect planning. Ancestral humans transported tools and tool-making materials as well as food items. Wild chimpanzees also transport selected hammer tools and nuts to anvil sites. To date, we had no other examples of selection and transport of stone tools among wild nonhuman primates. Wild bearded capuchins (Cebus libidinosus) in Boa Vista (Piauí, Brazil) routinely crack open palm nuts and other physically well-protected foods on level surfaces (anvils) using stones (hammers) as percussive tools. Here we present indirect evidence, obtained by a transect census, that stones suitable for use as hammers are rare (study 1) and behavioral evidence of hammer transport by twelve capuchins (study 2). To crack palm nuts, adults transported heavier and harder stones than to crack other less resistant food items. These findings show that wild capuchin monkeys selectively transport stones of appropriate size and hardness to use as hammers, thus exhibiting, like chimpanzees and humans, planning in tool-use activities.     

Variability in an early hominin percussive tradition: the Acheulean versus cultural variation in modern chimpanzee artefacts

Percussion makes a vital link between the activities of early human ancestors and other animals in tool-use and tool-making. Far more of the early human actions are preserved as archaeology, since the percussion was largely used for making hard tools of stone, rather than for direct access to food. Both primate tools and early hominin tools, however, offer a means to exploring variability in material culture, a strong focus of interest in recent primate studies. This paper charts such variability in the Acheulean, the longest-lasting tool tradition, extant form about 1.7 to about 0.1 Ma, and well known for its characteristic handaxes. The paper concentrates on the African record, although the Acheulean was also known in Europe and Asia. It uses principal components and discriminant analysis to examine the measurements from 66 assemblages (whole toolkits), and from 18 sets of handaxes. Its review of evidence confirms that there is deep-seated pattern in the variation, with variability within a site complex often matching or exceeding that between sites far distant in space and time. Current techniques of study allow comparisons of handaxes far more easily than for other components, stressing a need to develop common practice in measurement and analysis. The data suggest, however, that a higher proportion of traits recurs widely in Acheulean toolkits than in the chimpanzee record.     

Chaînes opératoires and resource-exploitation strategies in chimpanzee (Pan troglodytes) nut cracking

We apply archaeological methods to extend our knowledge of chimpanzee material culture. The cha?ne opératoire conceptual framework, as introduced by ethnography, established technology as a phased process. Prehistoric archaeology adopted this concept to elucidate technological variability in tool-making procedures, based on knowledge of tool functions or subsistence patterns. We focused on the detection of operational sequences by wild chimpanzees (Pan troglodytes verus) when nut cracking with lithic implements at the sites of Bossou and Diecké, Guinea, West Africa. Thus, while it has recently been claimed that chimpanzees leave behind recognizable assemblages of stone hammers that can be morphologically distinguished from Oldowan hammers, this is the first study to focus specifically on the existence of operational sequences during the utilization of stone tools by wild chimpanzees. By combining primatological and archaeological methods and examining ecological areas inhabited by different chimpanzee groups, we sought technological variability and identified variables influencing regional diversity in tool typology and technology. We compared three case studies: (1) Bossou-direct recording of experimental nut-cracking sessions; (2) Bossou- direct and indirect monitoring of nut-cracking sites in the wild; (3) Diecké-indirect monitoring of nut-cracking sites in the wild. Results suggest that chimpanzees perform sequences of repeated tool transport and nut cracking. Data show discrimination of tool functions based on tool features. We identified the most technologically complex tool for nut cracking, which was composed of four stones. We found regional diversity in chimpanzee stone assemblages. Raw-material type and tool mobility constrain technological development in human and nonhuman primates. Spatial analysis of tool distribution indicates a pattern of resource-exploitation strategy, revealing affinities with Oldowan.     

Stone tool analysis and human origins research: some advice from Uncle Screwtape

The production of purposefully fractured stone tools with functional, sharp cutting edges is a uniquely derived hominin adaptation. In the long history of life on earth, only hominins have adopted this remarkably expedient and broadly effective technological strategy. In the paleontological record, flaked stone tools are irrefutable proof that hominins were present at a particular place and time. Flaked stone tools are found in contexts ranging from the Arctic to equatorial rainforests and on every continent except Antarctica. Paleolithic stone tools show complex patterns of variability, suggesting that they have been subject to the variable selective pressures that have shaped so many other aspects of hominin behavior and morphology. There is every reason to expect that insights gained from studying stone tools should provide vital and important information about the course of human evolution. And yet, one senses that archeological analyses of Paleolithic stone tools are not making as much of a contribution as they could to the major issues in human origins research.     

Behavioral inferences from Early Stone artifact assemblages: an experimental model

A methodological approach for assessing the nature and palaeographic distribution of early stone artifact assemblages is presented, modeled after an approach originally used for faunal analysis. By combining experimental replicative studies with careful analysis of Palaeolithic archaeological occurrences, it is potentially possible to reconstruct entire technological systems and to assess what stages of lithic reduction may be preferentially represented at high density artifact concentrations that we normally call archaeological “sites”, and what stages of reduction are found in lower density (“off site”) scatters.Based upon the results of this approach, alternative explanations for certain stages of lithic reduction being preferentially represented at a number of Plio-Pleistocene archaeological sites at Koobi Fora, Kenya are considered and evaluated with regard to early hominid organizational patterns. It appears that hominid stone technology was a relatively complex system by 1·9 to 1·4 million years B.P., involving significant transport and carrying of stone artifacts representing various stages of reduction and suggesting more foresight and planning than observed among extant nonhuman primates.The application of this approach to other Palaeolithic occurrences should enable anthropologists to obtain a better understanding of the organizational patterns of tool-making hominids throughout the course of human evolution.     

Early Origin for Human-Like Precision Grasping: A Comparative Study of Pollical Distal Phalanges in Fossil Hominins

Background

The morphology of human pollical distal phalanges (PDP) closely reflects the adaptation of human hands for refined precision grip with pad-to-pad contact. The presence of these precision grip-related traits in the PDP of fossil hominins has been related to human-like hand proportions (i.e. short hands with a long thumb) enabling the thumb and finger pads to contact. Although this has been traditionally linked to the appearance of stone tool-making, the alternative hypothesis of an earlier origin—related to the freeing of the hands thanks to the advent of terrestrial bipedalism—is also possible given the human-like intrinsic hand proportion found in australopiths.

Methodology/Principal Findings

We perform morphofunctional and morphometric (bivariate and multivariate) analyses of most available hominin pollical distal phalanges, including Orrorin, Australopithecus, Paranthropous and fossil Homo, in order to investigate their morphological affinities. Our results indicate that the thumb morphology of the early biped Orrorin is more human-like than that of australopiths, in spite of its ancient chronology (ca. 6 Ma). Moreover, Orrorin already displays typical human-like features related to precision grasping.

Conclusions

These results reinforce previous hypotheses relating the origin of refined manipulation of natural objects–not stone tool-making–with the relaxation of locomotor selection pressures on the forelimbs. This suggests that human hand length proportions are largely plesiomorphic, in the sense that they more closely resemble the relatively short-handed Miocene apes than the elongated hand pattern of extant hominoids. With the advent of terrestrial bipedalism, these hand proportions may have been co-opted by early hominins for enhanced manipulative capabilities that, in turn, would have been later co-opted for stone tool-making in the genus Homo, more encephalized than the previous australopiths. This hypothesis remains may be further tested by the finding of more complete hands of unequivocally biped early hominins.     

Cortical motor asymmetry and hominid feeding strategies

Homo sapiens differs from all other primates in having a cerebrum that is markedly asymmetrical for a number of functions, including motor control of the hands. The ability to coordinate the two hands while each is engaged in a different task is not highly developed in non-human primates and may have been an important behavioral distinction between early apes and hominids. These skills are necessary for tool-making, and probably arose selectively as a feeding strategy to exploit an expanding food base. It is proposed that bimanual motor asymmetry follows bipedalism but precedes tool-making as a step in the process of hominization.     

Precision grips,hand morphology,and tools

This study asks whether there are discernable links between precision gripping, tool behaviors,

1 The term “tool behavior” has been variously used in the literature, in some cases implying exclusively tool making distinctive of humans (Susman, 1991) and in others referring variably to tool using and/or tool-making abilities, some shared with us by other animals (Susman, 1988a,b, 1994). In this paper the term is used to include both tool using and tool making behaviors of humans and non-humans; the term “tool making” is used in place of “tool behavior” whenever the discussion is focused upon distinguishing a capacity for removing flakes from stone preforms from a more general capacity to manipulate stone tools.

and hand morphology in modern hominoids, which may guide functional interpretation of early hominid hand morphology. Findings from a three-pronged investigation answer this question in the affirmative, as follows. (1) Experimental manufacture of early prehistoric tools provides evidence of connections between distinctive human precision grips and effective tool making. (A connection is not found between the “fine” thumb/index finger pad precision grip and early tool making.) (2) Manipulative behavior studies of chimpanzees, hamadryas baboons, and humans show that human precision grips are distinguished by the greater force with which objects may be secured by the thumb and fingers of one hand (precision pinching) and the ability to adjust the orientation of gripped objects through movements at joints distal to the wrist (precision handling). (3) Morphological studies reveal eight features distinctive of modern humans which facilitate use of these grips. Among these features are substantially larger moment arms for intrinsic muscles that stabilize the proximal thumb joints. Examination of evidence for these reveals that three of the eight features occur in Australopithecus afarensis, but limited thumb mobility would have compromised tool making. Also, Olduvai hand morphology strongly suggests a capacity for stone tool making. However, functional and behavioral implications of Sterkfontein and Swartkrans hand morphology are less clear. At present, no single skeletal feature can be safely relied upon as an indicator of distinctively human capabilities for precision gripping or tool making in fossil hominids. Am J Phys Anthropol 102:91–110, 1997. © 1997 Wiley-Liss, Inc.     

Mass spectrometric U-series dating of Huanglong Cave in Hubei Province,central China: Evidence for early presence of modern humans in eastern Asia

Most researchers believe that anatomically modern humans (AMH) first appeared in Africa 160-190 ka ago, and would not have reached eastern Asia until ∼50 ka ago. However, the credibility of these scenarios might have been compromised by a largely inaccurate and compressed chronological framework previously established for hominin fossils found in China. Recently there has been a growing body of evidence indicating the possible presence of AMH in eastern Asia ca. 100 ka ago or even earlier. Here we report high-precision mass spectrometric U-series dating of intercalated flowstone samples from Huanglong Cave, a recently discovered Late Pleistocene hominin site in northern Hubei Province, central China. Systematic excavations there have led to the in situ discovery of seven hominin teeth and dozens of stone and bone artifacts. The U-series dates on localized thin flowstone formations bracket the hominin specimens between 81 and 101 ka, currently the most narrow time span for all AMH beyond 45 ka in China, if the assignment of the hominin teeth to modern Homo sapiens holds. Alternatively this study provides further evidence for the early presence of an AMH morphology in China, through either independent evolution of local archaic populations or their assimilation with incoming AMH. Along with recent dating results for hominin samples from Homo erectus to AMH, a new extended and continuous timeline for Chinese hominin fossils is taking shape, which warrants a reconstruction of human evolution, especially the origins of modern humans in eastern Asia.     

Fat Residue and Use-Wear Found on Acheulian Biface and Scraper Associated with Butchered Elephant Remains at the Site of Revadim,Israel

The archaeological record indicates that elephants must have played a significant role in early human diet and culture during Palaeolithic times in the Old World. However, the nature of interactions between early humans and elephants is still under discussion. Elephant remains are found in Palaeolithic sites, both open-air and cave sites, in Europe, Asia, the Levant, and Africa. In some cases elephant and mammoth remains indicate evidence for butchering and marrow extraction performed by humans. Revadim Quarry (Israel) is a Late Acheulian site where elephant remains were found in association with characteristic Lower Palaeolithic flint tools. In this paper we present results regarding the use of Palaeolithic tools in processing animal carcasses and rare identification of fat residue preserved on Lower Palaeolithic tools. Our results shed new light on the use of Palaeolithic stone tools and provide, for the first time, direct evidence (residue) of animal exploitation through the use of an Acheulian biface and a scraper. The association of an elephant rib bearing cut marks with these tools may reinforce the view suggesting the use of Palaeolithic stone tools in the consumption of large game.     

New Archaeological Evidence for an Early Human Presence at Monte Verde,Chile

Questions surrounding the chronology, place, and character of the initial human colonization of the Americas are a long-standing focus of debate. Interdisciplinary debate continues over the timing of entry, the rapidity and direction of dispersion, the variety of human responses to diverse habitats, the criteria for evaluating the validity of early sites, and the differences and similarities between colonization in North and South America. Despite recent advances in our understanding of these issues, archaeology still faces challenges in defining interdisciplinary research problems, assessing the reliability of the data, and applying new interpretative models. As the debates and challenges continue, new studies take place and previous research reexamined. Here we discuss recent exploratory excavation at and interdisciplinary data from the Monte Verde area in Chile to further our understanding of the first peopling of the Americas. New evidence of stone artifacts, faunal remains, and burned areas suggests discrete horizons of ephemeral human activity in a sandur plain setting radiocarbon and luminescence dated between at least ~18,500 and 14,500 cal BP. Based on multiple lines of evidence, including sedimentary proxies and artifact analysis, we present the probable anthropogenic origins and wider implications of this evidence. In a non-glacial cold climate environment of the south-central Andes, which is challenging for human occupation and for the preservation of hunter-gatherer sites, these horizons provide insight into an earlier context of late Pleistocene human behavior in northern Patagonia.