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.     

Chimpanzee and human grips: A new classification with a focus on evolutionary morphology

We observed grips by the hand during locomotor and manipulative behavior of captive chimpanzees to improve our ability to interpret differences between chimpanzees and humans in hand morphology that are not easily explained by current behavioral data. The study generated a new classification of grips,which takes into account three elements of precision and power gripping that appear to distinguish between the chimpanzees and humans, and which have not been explored previously in relation to hand morphology. These elements are (1) the relative force of the precision grips (pinch versus hold), (2) the relative ability to translate and rotate objects by the thumb and fingers (precision handling), and (3) the relative ability to orient a cylindrical object so that it functions effectively as an extension of the forearm (power squeeze). We recommend that this classification be incorporated into protocols for field and laboratory studies of nonhuman primate manipulative behavior, in order to test our prediction that these three elements clearly distinguish humans from chimpanzees and other nonhuman primates. The results of this test will have direct bearing upon decisions as to which grips (with their associated behaviors) are most likely to guide us through kinematic and kinetic analysis to possible explanations for morphological differences between humans and other species. These explanations, in turn, are fundamental to our ability to discern evidence for potential grips and tool behaviors in the manual morphology of fossil hominids.     

Tool making,hand morphology and fossil hominins

Was stone tool making a factor in the evolution of human hand morphology? Is it possible to find evidence in fossil hominin hands for this capability? These questions are being addressed with increasingly sophisticated studies that are testing two hypotheses; (i) that humans have unique patterns of grip and hand movement capabilities compatible with effective stone tool making and use of the tools and, if this is the case, (ii) that there exist unique patterns of morphology in human hands that are consistent with these capabilities. Comparative analyses of human stone tool behaviours and chimpanzee feeding behaviours have revealed a distinctive set of forceful pinch grips by humans that are effective in the control of stones by one hand during manufacture and use of the tools. Comparative dissections, kinematic analyses and biomechanical studies indicate that humans do have a unique pattern of muscle architecture and joint surface form and functions consistent with the derived capabilities. A major remaining challenge is to identify skeletal features that reflect the full morphological pattern, and therefore may serve as clues to fossil hominin manipulative capabilities. Hominin fossils are evaluated for evidence of patterns of derived human grip and stress-accommodation features.     

Capuchin monkey (Cebus apella) grips for the use of stone tools

This research examined capuchin monkey (Cebus apella) grips for the use of throwing, nut-cracking, and cutting tools. We provided subjects with stones and apparatus that accommodated the use of stones as tools. Our subjects exhibited five grips, two of which the animals used when force was the primary consideration (power grips) and three of which the animals use when accuracy of sensory judgment and instrumentation was required (precision grips). We believe that the range of contexts in which capuchins use stone tools, combined with the ability of capuchins to employ both power and precision grips as part of their tool repertoire, indicate that Cebus apella can be used to identify grips that facilitated hominid lithic technology. Am J Phys Anthropol 103:131–135, 1997. © 1997 Wiley-Liss, Inc.     

Comparative 3D quantitative analyses of trapeziometacarpal joint surface curvatures among living catarrhines and fossil hominins

Comparisons of joint surface curvature at the base of the thumb have long been made to discern differences among living and fossil primates in functional capabilities of the hand. However, the complex shape of this joint makes it difficult to quantify differences among taxa. The purpose of this study is to determine whether significant differences in curvature exist among selected catarrhine genera and to compare these genera with hominin¹ fossils in trapeziometacarpal curvature. Two 3D approaches are used to quantify curvatures of the trapezial and metacarpal joint surfaces: (1) stereophotogrammetry with nonuniform rational B‐spline (NURBS) calculation of joint curvature to compare modern humans with captive chimpanzees and (2) laser scanning with a quadric‐based calculation of curvature to compare modern humans and wild‐caught Pan, Gorilla, Pongo, and Papio. Both approaches show that Homo has significantly lower curvature of the joint surfaces than does Pan. The second approach shows that Gorilla has significantly more curvature than modern humans, while Pongo overlaps with humans and African apes. The surfaces in Papio are more cylindrical and flatter than in Homo. Australopithecus afarensis resembles African apes more than modern humans in curvatures, whereas the Homo habilis trapezial metacarpal surface is flatter than in all genera except Papio. Neandertals fall at one end of the modern human range of variation, with smaller dorsovolar curvature. Modern human topography appears to be derived relative to great apes and Australopithecus and contributes to the distinctive human morphology that facilitates forceful precision and power gripping, fundamental to human manipulative activities. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc. ¹ The term “hominin” refers to members of the tribe Hominini, which includes modern humans and fossil species that are related more closely to modern humans than to extant species of chimpanzees, Wood and Lonergan (2008). Hominins are in the family Hominidae with great apes.     

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.     

Skeletal evidence for precision gripping inCebus apella

We compared the thumb morphology ofCebus apella to that of several other primate species in order to determine whether robust thumbs are associated with tool-use. We found that thumb robusticity was greater forCebus apella than for all other represented nonhuman species exceptGorilla gorilla. Further, thumb robusticity inCebus apella was similar to that ofAustralopithecus afarensis but lesser than that of other represented hominids, including modern humans. We propose that precision gripping similar to that which occurs in tool-using context amongCebus probably occurred among Australopithecines prior to the emergence of sophisticated tool behavior amongHomo andParanthropus.     

Hand biomechanics during simulated stone tool use

Human radial digits have derived features compared with apes, with long robust thumbs, relatively larger joint surfaces, and hypertrophic thenar muscles. Here we test the hypothesis that these features evolved in the context of making and using stone tools, specifically for producing large gripping forces and for countering large joint contact stresses. We used portable force plates simulating early stone tools to: 1) document and compare the magnitude of external/internal forces and joint stresses in the radial digits during hardhammer percussion and flake use, and 2) examine how variation in digit morphology affects muscle and joint mechanics during stone tool use. Force and kinematic data were collected from a sample representing normal variation in digit morphology (n = 25). The effects of digit size/shape on digit biomechanics were evaluated using partial correlations, controlling for tool reaction forces and impact velocities. Results show that individuals with longer digits require relatively less muscle force to stabilize digital joints, and are exposed to relatively lower joint contact stresses during stone tool use, due in part to an increase in the robusticity of metacarpals and phalanges in humans relative to chimpanzees. These analyses further suggest that Pan- or australopith-like pollical anatomy presents serious performance challenges to habitual tool use. Our data support the hypothesis that evolutionary increases in thumb length, robusticity, and thenar muscle mass enabled Homo to produce more force and to tolerate higher joint stresses during tool use.     

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.     

Grasping behavior in tufted capuchin monkeys (Cebus apella): grip types and manual laterality for picking up a small food item

This study investigates prehension in 20 tufted capuchins (Cebus apella) in a reaching task requiring individuals to grasp a small food item fixed to a tray. The aim was twofold: 1) to describe capuchins' grasping techniques in detail, focusing on digit movements and on different areas of contact between the grasping fingers; and 2) to assess the relationship between grip types and manual laterality in this species. Capuchins picked up small food items using a wide variety of grips. In particular, 16 precision grip variants and 4 power grip variants were identified. The most frequently used precision grip involved the distal lateral areas of the thumb and the index finger, while the most preferred kind of power grip involved the thumb and the palm, with the thumb being enclosed by the other fingers. Immature capuchins picked up small food items using power grips more often than precision grips, while adult individuals exhibited no significant preference for either grip type. The analysis performed on the time capuchins took to grasp the food and withdraw it from the tray hole revealed that 1) precision grips were as efficient as power grips; 2) for precision grips, the left hand was faster than the right hand; and 3) for power grips, both hands were equally quick. Hand preference analysis, based on the frequency for the use of either hand for grasping actions, revealed no significant hand bias at group level. Likewise, there was no significant relationship between grip type and hand preference.     

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.     

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.     

The enhanced tool‐kit of two groups of wild bearded capuchin monkeys in the Caatinga: tool making,associative use,and secondary tools

The use of stones to crack open encapsulated fruit is widespread among wild bearded capuchin monkeys (Cebus libidinosus) inhabiting savanna‐like environments. Some populations in Serra da Capivara National Park (Piauí, Brazil), though, exhibit a seemingly broader toolkit, using wooden sticks as probes, and employing stone tools for a variety of purposes. Over the course of 701.5 hr of visual contact of two wild capuchin groups we recorded 677 tool use episodes. Five hundred and seventeen of these involved the use of stones, and 160 involved the use of sticks (or other plant parts) as probes to access water, arthropods, or the contents of insects' nests. Stones were mostly used as “hammers”—not only to open fruit or seeds, or smash other food items, but also to break dead wood, conglomerate rock, or cement in search of arthropods, to dislodge bigger stones, and to pulverize embedded quartz pebbles (licking, sniffing, or rubbing the body with the powder produced). Stones also were used in a “hammer‐like” fashion to loosen the soil for digging out roots and arthropods, and sometimes as “hoes” to pull the loosened soil. In a few cases, we observed the re‐utilization of stone tools for different purposes (N=3), or the combined use of two tools—stones and sticks (N=4) or two stones (N=5), as sequential or associative tools. On three occasions, the monkeys used smaller stones to loosen bigger quartz pebbles embedded in conglomerate rock, which were subsequently used as tools. These could be considered the first reports of secondary tool use by wild capuchin monkeys. Am. J. Primatol. 71:242–251, 2009. © 2008 Wiley‐Liss, Inc.     

A clarification of Pouydebat et al., 2008, evolution of grasping among anthropoids

Several statements by Pouydebat et al. (2008) do not adequately represent views of authors cited, in part because they reflect confusion in the literature about terminology regarding precision gripping. We address these problems, by tracing definitions of precision grips through the literature on manipulative behaviour and identifying the grip that is central to the Pouydebat et al. (2008) study. This allows us to offer a clarification of the statements by Pouydebat et al. (2008) regarding the sequence of appearance of human grip capabilities and possible morphological correlates to these capabilities in extant species.     

Compound grips in tufted capuchin monkeys (Sapajus spp and Sapajus libidinosus)

An experimental study with captive individuals and study of video recordings of wild monkeys explored whether and how tufted capuchin monkeys use onehand to hold one or more objects with multiple grips (compound grips). A task designed to elicit compound grip was presented to five captive tufted capuchin monkeys (Sapajus spp). The monkeys held one to four balls in onehand and dropped the balls individually into a vertical tube. Multiple simple grips and independent digit movements enabled separate control of multiple objects in one hand. Monkeys always supported the wrist on the horizontal edge of the tube before releasing the ball. Increasing the number of balls decreased the likelihood that the monkeys managed the task. Wild bearded capuchins (Sapajus libidinosus) used compound grips spontaneously to store multiple food items. Compound grips have been described in macaques, gorillas, chimpanzees, and humans, and now in a New World primate. We predict that any primate species that exhibits precision grips and independent digit movement can perform compound grips. Our findings suggest many aspects of compound grip that await investigation.     

A whole new world of ancestors: Eocene anthropoideans from Africa

The last decade has witnessed enormous gains in our knowledge of early anthro-poidean primates,

1 “Anthropoidean” refers to members of the suborder Anthropoidea, whch contaings New and Old world monkeys, apes, and humans. These primates are also often called “simians,” “simiiforms” or “anthropoids;” the latter term is potentially confusing because it has often been used to refer only to the great apes.

the oldest known relatives of monkeys, apes and humans. Recent fossil finds in Egypt, Algeria, Tunisia, and Oman, along with the associated geological research at these sites, have radically changed our models of anthro-poidean origins and differentiation. Instead of first appearing as robust-jawed herbivorous primates in the earliest Oligocene, it is now apparent that there was radiation of small-bodied, fruit-and-insect-eating anthropoideans during the Eocene. These early forms included at least two oligopithecines (squirrel-monkey-sized primates with a catarrhine dental formula) and two early “parapithecid monkeys” (three-premolared primates with lumpy, bunodont dentitions). In addition, several smaller species from Algeria and Egypt, ranging in size from pygmy marmosets to tamarins, are not definitely assignable to previously known families. Alongside the early anthropoideans, there are also at least four recently identified prosimian families. The continental Eocene of Africa—for years, little more than a blank on the paieontologi-cal map—now comprises an increasingly productive field source of new data that is important in deciphering phyletic and adaptive aspects of the prosimian-anthropoid transition.     

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.     

Functional morphology of amplexus (clasping) in spinicaudatan clam shrimps (Crustacea,Branchiopoda) and its evolution in bivalved branchiopods: A video‐based analysis

Male clam shrimps (Crustacea: Branchiopoda: Laevicaudata, Spinicaudata, and Cyclestherida) have their first one or two trunk limb pairs modified as “claspers,” which are used to hold the female during mating and mate guarding. Clasper morphology has traditionally been important for clam shrimp taxonomy and classification, but little is known about how the males actually use the claspers during amplexus (clasping). Homologies of the various clasper parts (“movable finger,” “large palp,” “palm,” “gripping area,” and “small palp”) have long been discussed between the three clam shrimp taxa, and studies have shown that only some structures are homologous while others are convergent (“partial homology”). We studied the clasper functionality in four spinicaudatan species using video recordings and scanning electron microscopy, and compared our results with other clam shrimp groups. General mating behavior and carapace morphology was also studied. Generally, spinicaudatan and laevicaudatan claspers function similarly despite some parts being nonhomologous. We mapped clasper morphology and functionality aspects on a branchiopod phylogeny. We suggest that the claspers of the three groups were adapted from an original, simpler clasper, each for a “stronger” grip on the female's carapace margin: 1) Spinicaudata have two clasper pairs bearing an elongated apical club/gripping area with one setal type; 2); Cyclestherida have one clasper pair with clusters of molariform setae on the gripping area and at the movable finger apex; and 3) Laevicaudata have one clasper pair, but have incorporated an additional limb portion into the clasper palm and bear a diverse set of setae. J. Morphol. 278:523–546, 2017. © 2017 Wiley Periodicals, Inc.     

Comparative morphology of the pollical distal phalanx

Functional analysis of human pollical distal phalangeal (PDP) morphology is undertaken to establish a basis for the assessment of fossil hominid PDP morphology. Features that contribute to the effectiveness of grips involving the distal thumb and finger pulp areas include: 1) distal thumb interphalangeal joint morphology, facilitating PDP conjunct pronation with flexion; 2) differentiation of a proximal, mobile pulp region from a distal, stable pulp region, providing for firm precision pinch grips and precision handling of objects; and 3) asymmetric attachment of the flexor pollicis longus (FPL) tendon fibers, favoring PDP conjunct pronation. A proportionately larger size of the ulnar vs. radial ungual spine suggests differential loading intensity of the ulnar side of the proximal ungual pulp and supporting nail bed. Stresses at the distal interphalangeal joint are indicated by the presence of a sesamoid bone within the volar (palmar) plate, which also increases the length of the flexor pollicis longus tendon moment arm. Dissections of specimens from six nonhuman primate genera indicate that these human features are shared variably with individuals in other species, although the full pattern of features appears to be distinctively human. Humans share variably with these other species all metric relationships examined here. The new data identify a need to systematically review long-standing assumptions regarding the range of precision and power manipulative capabilities that might reasonably be inferred from morphology of the distal phalangeal tuberosity and from the FPL tendon insertion site on the PDP.