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.     

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.     

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.     

Evolution of the power ("squeeze") grip and its morphological correlates in hominids.

The "squeeze" form of power grip is investigated for the purposes of clarifying the hand posture and activities associated with the grip, assessing the potential in chimpanzees for using the grip, and identifying morphological correlates of an effective power grip that may be recognized in fossil hominid species. Our approaches include: (1) the analysis of the human grip, focusing on both the hand posture involved and hand movements associated with use of the grip in hammering; (2) the analysis of similar chimpanzee grips and associated movements; (3) comparative functional analysis of regions in the hand exploited and stressed by the grip and its associated movements in humans; and (4) a review of the literature on the power grip and its morphological correlates. Results of the study indicate that humans use a squeeze form of power grip effectively to wield cylindrical tools forcefully as extensions of the forearm. Several morphological features occur in high frequency among humans which facilitate the grip and are consistent with the large internal and external forces associated with it in hammering and in other tool-using activities. Chimpanzee hand postures resembling this form of human power grip are not fully comparable and lack some of these morphological correlates that facilitate its use. The hand of Australopithecus afarensis does not appear to have been stressed by use of the grip, but there is some evidence for this type of stress in the metacarpals from Sterkfontein Member 4. Hands from Olduvai and Swartkrans do not provide sufficient evidence for assessment of power grip capabilities.     

Was Australopithecus afarensis able to make the Lomekwian stone tools? Towards a realistic biomechanical simulation of hand force capability in fossil hominins and new insights on the role of the fifth digit

While no consensus allows explaining how and when human-like traits arose in fossil hominin hands, the recent discoveries of the Lomekwian stone tools (3.3 Ma) support the view that early hominins were able to use forceful grips in order to manipulate large-sized blocks for pounding activities. Then, assessing gripping abilities of contemporaneous hominin, i.e. Australopithecus afarensis, is necessary, particularly with regards to its unusual 5th ray morphology that has been deemed crucial to ensure forceful grips. Here, we present a musculoskeletal simulation based on the A. afarensis hand morphology that includes an original 5th carpometacarpal joint. Our first results suggest a limited influence of muscle parameters (e.g., PCSA) and support the value of simulations for studying extinct taxa even in absence of soft-tissue data. Given the inability for the pulp of the 5th ray to face the surface of a large-sized object, the A. afarensis hand would have had limited possibility to exert sufficient force to make the Lomekwian stone tools.     

Evidence in hand: recent discoveries and the early evolution of human manual manipulation

For several decades, it was largely assumed that stone tool use and production were abilities limited to the genus Homo. However, growing palaeontological and archaeological evidence, comparative extant primate studies, as well as results from methodological advancements in biomechanics and morphological analyses, have been gradually accumulating and now provide strong support for more advanced manual manipulative abilities and tool-related behaviours in pre-Homo hominins than has been traditionally recognized. Here, I review the fossil evidence related to early hominin dexterity, including the recent discoveries of relatively complete early hominin hand skeletons, and new methodologies that are providing a more holistic interpretation of hand function, and insight into how our early ancestors may have balanced the functional requirements of both arboreal locomotion and tool-related behaviours.     

Grips and hand movements of chimpanzees during feeding in Mahale Mountains National Park,Tanzania

It has long been assumed that stone tool making was a major factor in the evolution of derived hominin hand morphology. However, stresses on the hand associated with food retrieval and processing also have been recognized as relevant early hominin behaviors that should be investigated. To this end, chimpanzee food manipulation was videotaped in the Mahale Mountains National Park, Tanzania. Grips and hand movements by 39 chimpanzees were analyzed for arboreal and terrestrial feeding involving 10 food‐types and associated vegetation. It was predicted that (1) new grips would be found that had not been observed in captivity, (2) forceful precision grips would be absent from the repertoire, as in captivity, and (3) precision handling would be observed. New grips involving the full thumb and buttressed index finger, and a new integrated pattern of grips and forceful hand movements were discovered, associated with feeding on large fruits and meat. Participation of the full thumb in these grips, rather than the distal thumb and fingers, throws light on feeding behaviors that may have become increasingly significant factors in the evolution of derived hominin thumb morphology. The proximal thumb stabilizes food with the flexed index finger against the pull of the teeth and provides leverage in breaking food into portions. Isolated qualitative observations of possibly forceful pinch by the thumb and side of the index finger highlight the need for comparative quantitative data to test whether humans are unique in forceful precision gripping capability. Precision handling was not seen. Am J Phys Anthropol 156:317–326, 2015. © 2014 Wiley Periodicals, Inc.     

Modes de sélection et contraintes en Europe centrale prénéanderthalienne

The Microlithic industries of lower Palaeolithic central Europe have been speculated to be a result of raw material availability and therefore natural constraints. However, on some sites such as Bilzingsleben and Vertessz?ll?s, raw material constraints do not apply. Clearly here has been a positive selection for small-scale tools that must have different explanations. The seemingly stable pattern of forms unrelated to raw material properties, leads to the inference that early hominin societies possessed and transmitted over generations, a defined set of behavioural norms. The paper argues that patterns of choice can be isolated within lower Palaeolithic stone tool assemblages that are distinct from patterns of ecological restraint.     

The Jinniushan hominin pedal skeleton from the late Middle Pleistocene of China

Bipedalism has long been recognized as the seminal adaptation of the hominin radiation and thus used to distinguish hominins from great ape fossils. Notwithstanding preconceptions and varied interpretations, the distinctive features of the modern human foot and accompanying striding gait, appear to be recent innovations that are largely absent in the earliest facultative bipeds. These distinctive features are mainly components of fixed longitudinal and transverse pedal arches, and of a uniquely derived hallucal metatarsophalangeal joint. They enhance ankle joint plantar flexor function and accommodate localized peak plantar pressures at the medial ball during terminal stance. To date, the paleontological record has yielded very little of the hominin foot, especially of the Middle Pleistocene hominins. New specimens from this time interval should help provide insights into the timing and pattern of what appears to be a mosaic pattern of evolution of the modern human foot features. Here we describe the fossil hominin foot skeleton recovered from the Jinniushan site, Liaoning Province, People's Republic of China. It affords a singular glimpse of the pedal morphology of a late Middle Pleistocene hominin (c.f. Homo heidlebergensis). Dated to 200 ka or older, this foot offers the earliest evidence for increased stability of the medial longitudinal arch, while retaining a number of primitive features apparently characteristic of robust premodern hominins, including lower arches and a less stable hallucal metatarsophalangeal joint (medial ball) than in modern humans. These features reflect different foot capabilities and suggest the bipedal stride of the Jinniushan hominin differed subtlety from that of modern humans.     

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.     

Hand before foot? Cortical somatotopy suggests manual dexterity is primitive and evolved independently of bipedalism

People have long speculated whether the evolution of bipedalism in early hominins triggered tool use (by freeing their hands) or whether the necessity of making and using tools encouraged the shift to upright gait. Either way, it is commonly thought that one led to the other. In this study, we sought to shed new light on the origins of manual dexterity and bipedalism by mapping the neural representations in the brain of the fingers and toes of living people and monkeys. Contrary to the ‘hand-in-glove’ notion outlined above, our results suggest that adaptations underlying tool use evolved independently of those required for human bipedality. In both humans and monkeys, we found that each finger was represented separately in the primary sensorimotor cortex just as they are physically separated in the hand. This reflects the ability to use each digit independently, as required for the complex manipulation involved in tool use. The neural mapping of the subjects’ toes differed, however. In the monkeys, the somatotopic representation of the toes was fused, showing that the digits function predominantly as a unit in general grasping. Humans, by contrast, had an independent neurological representation of the big toe (hallux), suggesting association with bipedal locomotion. These observations suggest that the brain circuits for the hand had advanced beyond simple grasping, whereas our primate ancestors were still general arboreal quadrupeds. This early adaptation laid the foundation for the evolution of manual dexterity, which was preserved and enhanced in hominins. In hominins, a separate adaptation, involving the neural separation of the big toe, apparently occurred with bipedality. This accords with the known fossil evidence, including the recently reported hominin fossils which have been dated to 4.4 million years ago.     

Neanderthals

Neanderthals are a group of fossil humans that inhabited Western Eurasia from approximately 300 to 30,000 years ago (ka). They vanished from the fossil record a few millennia after the first modern humans appeared in Europe (ca. 40 ka BP). They are characterized by a unique combination of distinctive anatomical features, and are found with stone tools of the Mousterian stone tool industry. Current consensus views them as a distinct Eurasian human lineage isolated from the rest of the Old World and sharing a common ancestor with modern humans sometime in the early Middle Pleistocene. The extreme cold of the European Ice Ages is considered at least partly responsible for the evolution of some of the distinctive Neanderthal anatomy, although other factors (functional demands, effects of chance in small populations) were probably also important. The causes for the Neanderthal extinction are not well understood. Worsening climate and competition with modern humans are implicated. Neanderthals were our sister species, much more closely related to us than the chimpanzees, our closest living relatives are today.     

Understanding Ancient Hominin Dispersals Using Artefactual Data: A Phylogeographic Analysis of Acheulean Handaxes

Background

Reconstructing the dispersal patterns of extinct hominins remains a challenging but essential goal. One means of supplementing fossil evidence is to utilize archaeological evidence in the form of stone tools. Based on broad dating patterns, it has long been thought that the appearance of Acheulean handaxe technologies outside of Africa was the result of hominin dispersals, yet independent tests of this hypothesis remain rare. Cultural transmission theory leads to a prediction of a strong African versus non-African phylogeographic pattern in handaxe datasets, if the African Acheulean hypothesis is to be supported.

Methodology/Principal Findings

Here, this prediction is tested using an intercontinental dataset of Acheulean handaxes and a biological phylogenetic method (maximum parsimony). The analyses produce a tree consistent with the phylogeographic prediction. Moreover, a bootstrap analysis provides evidence that this pattern is robust, and the maximum parsimony tree is also shown to be statistically different from a tree constrained by stone raw materials.

Conclusions/Significance

These results demonstrate that nested analyses of behavioural data, utilizing methods drawn from biology, have the potential to shed light on ancient hominin dispersals. This is an encouraging prospect for human palaeobiology since sample sizes for lithic artefacts are many orders of magnitude higher than those of fossil data. These analyses also suggest that the sustained occurrence of Acheulean handaxe technologies in regions such as Europe and the Indian subcontinent resulted from dispersals by African hominin populations.     

Hand pressure distribution during Oldowan stone tool production

Modern humans possess a highly derived thumb that is robust and long relative to the other digits, with enhanced pollical musculature compared with extant apes. Researchers have hypothesized that this anatomy was initially selected for in early Homo in part to withstand high forces acting on the thumb during hard hammer percussion when producing stone tools. However, data are lacking on loads experienced during stone tool production and the distribution of these loads across the hand.Here we report the first quantitative data on manual normal forces (N) and pressures (kPa) acting on the hand during Oldowan stone tool production, captured at 200 Hz. Data were collected from six experienced subjects replicating Oldowan bifacial choppers. Our data do not support hypotheses asserting that the thumb experiences relatively high loads when making Oldowan stone tools. Peak normal force, pressure, impulse, and the pressure/time integral are significantly lower on the thumb than on digits 2 and/or digit 3 in every subject. Our findings call into question hypotheses linking modern human thumb robusticity specifically to load resistance during stone tool production.     

Upper limb kinematics and the role of the wrist during stone tool production

Past studies have hypothesized that aspects of hominin upper limb morphology are linked to the ability to produce stone tools. However, we lack the data on upper limb motions needed to evaluate the biomechanical context of stone tool production. This study seeks to better understand the biomechanics of stone tool‐making by investigating upper limb joint kinematics, focusing on the role of the wrist joint, during simple flake production. We test the hypotheses, based on studies of other upper limb activities (e.g., throwing), that upper limb movements will occur in a proximal‐to‐distal sequence, culminating in rapid wrist flexion just prior to strike. Data were captured from four amateur knappers during simple flake production using a VICON motion analysis system (50 Hz). Results show that subjects utilized a proximal‐to‐distal joint sequence and disassociated the shoulder joint from the elbow and wrist joints, suggesting a shared strategy employed in other contexts (e.g., throwing) to increase target accuracy. The knapping strategy included moving the wrist into peak extension (subject peak grand mean = 47.3°) at the beginning of the downswing phase, which facilitated rapid wrist flexion and accelerated the hammerstone toward the nodule. This sequence resulted in the production of significantly more mechanical work, and therefore greater strike forces, than would otherwise be produced. Together these results represent a strategy for increasing knapping efficiency in Homo sapiens and point to aspects of skeletal anatomy that might be examined to assess potential knapping ability and efficiency in fossil hominin taxa. Am J Phys Anthropol 143:134‐145, 2010. © 2010 Wiley‐Liss, Inc.     

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。     

Early evidence of the genus Homo in East Asia

The timing and route of the earliest dispersal from Africa to Eastern Asia are contentious topics in the study of early human evolution because Asian hominin fossil sites with precise age constraints are very limited. Here we report new high-resolution magnetostratigraphic results that place stringent age controls on excavated hominin incisors and stone tools from the Yuanmou Basin, southwest China. The hominin-bearing layer resides in a reverse polarity magnetozone just above the upper boundary of the Olduvai subchron, yielding an estimated age of 1.7Ma. The finding represents the age of the earliest documented presence of Homo, with affinities to Homo erectus, in mainland East Asia. This age estimate is roughly the same as for H. erectus in island Southeast Asia and immediately prior to the oldest archaeological evidence in northeast Asia. Mammalian fauna and pollen obtained directly from the hominin site indicate that the Yuanmou hominins lived in a varied habitat of open vegetation with patches of bushland and forest on an alluvial fan close to a lake or swamp. The age and location are consistent with a rapid southern migration route of initial hominin populations into Eastern Asia.     

A Neandertal mandible from the Cova del Gegant (Sitges, Barcelona, Spain)

A human mandible from the site of Cova del Gegant is described here for the first time and compared with other Middle and Upper Pleistocene representatives of the genus Homo from Europe and Southwest Asia. The specimen was recovered from sediments which also yielded Mousterian stone tools and Pleistocene fauna. The preserved morphology of the mandible, particularly in the region of the mental foramen, clearly aligns it with the Neandertals, making the Cova del Gegant the only known site in Catalonia documenting diagnostic human skeletal remains in association with Middle Paleolithic stone tools. This represents an important new addition to the human fossil record from the Iberian Peninsula and joins the Ba?olas mandible in documenting the course of human evolution in the northern Mediterranean region of Spain.     

Occasional,obligatory, and habitual stone tool use in hominin evolution

Archeologists have long assumed that earlier hominins were obligatory stone tool users. This assumption is deeply embedded in traditional ways of describing the lithic record. This paper argues that lithic evidence dating before 1.7 Ma reflects occasional stone tool use, much like that practiced by nonhuman primates except that it involved flaked‐stone cutting tools. Evidence younger than 0.3 Ma is more congruent with obligatory stone tool use, like that among recent humans. The onset of habitual stone tool use at about 1.7 Ma appears correlated with increased hominin logistical mobility (carrying things). The onset of obligatory stone tool use after 0.3 Ma may be linked to the evolution of spoken language. Viewing the lithic evidence dating between 0.3‐1.7 Ma as habitual stone tool use explains previously inexplicable aspects of the Early‐Middle Pleistocene lithic record.     

Using genetic evidence to evaluate four palaeoanthropological hypotheses for the timing of Neanderthal and modern human origins

A better understanding of the evolutionary relationship between modern humans and Neanderthals is essential for improving the resolution of hominin phylogenetic hypotheses. Currently, four distinct chronologies for the timing of population divergence are available, ranging from the late Middle Pleistocene to the late Early Pleistocene, each based on different interpretations of hominin taxonomy. Genetic data can present an independent estimate of the evolutionary timescale involved, making it possible to distinguish between these competing models of hominin evolution. We analysed five dated Neanderthal mitochondrial genomes, together with those of 54 modern humans, and inferred a genetic chronology using multiple age calibrations. Our mean date estimates are consistent with a process of genetic divergence within an ancestral population, commencing approximately 410-440 ka. These results suggest that a reappraisal of key elements in the Pleistocene hominin fossil record may now be required.