Emmanuelle Pouydebat

Biomechanical study of grasping according to the volume of the object: human versus non-human primates.

The evolution of the precision grips, in which an object is held between the distal surfaces of thumb and fingers and the power grip, in which an object is grasped with the palm, is poorly understood in spite of hypothesis stipulating an evolution from power toward precision grips. In human, numerous studies have shown that the external factors such as the size or the form of an object influenced grasp patterns whereas in non-human primates, those parameters are poorly known. The objective of the present study was to investigate the variation in the use of different grips according to the volume of the object for six primate species representative of the phylogeny: human, chimpanzee, orangutan, macaque, baboon and capuchin. For those species, the grasping patterns were examined during grasping of spherical objects of two different volumes. Frame-by-frame analysis of digit contact strategies indicated: (1) an effect of the species on the category of grasping whatever the volume of the object, (2) a high degree of species variability and (3) no individual difference whatever the species. These results are discussed in relation to its potential contribution to understand the evolution of grasping.

Getting a grip on tetrapod grasping: form, function, and evolution

Human beings have been credited with unparalleled capabilities for digital prehension grasping. However, grasping behaviour is widespread among tetrapods. The propensity to grasp, and the anatomical characteristics that underlie it, appear in all of the major groups of tetrapods with the possible exception of terrestrial turtles. Although some features are synapomorphic to the tetrapod clade, such as well‐defined digits and digital musculature, other features, such as opposable digits and tendon configurations, appear to have evolved independently in many lineages. Here we examine the incidence, functional morphology, and evolution of grasping across four major tetrapod clades. Our review suggests that the ability to grasp with the manus and pes is considerably more widespread, and ecologically and evolutionarily important, than previously thought. The morphological bases and ecological factors that govern grasping abilities may differ among tetrapods, yet the selective forces shaping them are likely similar. We suggest that further investigation into grasping form and function within and among these clades may expose a greater role for grasping ability in the evolutionary success of many tetrapod lineages.

Evolution of grasping among anthropoids

The prevailing hypothesis about grasping in primates stipulates an evolution from power towards precision grips in hominids. The evolution of grasping is far more complex, as shown by analysis of new morphometric and behavioural data. The latter concern the modes of food grasping in 11 species (one platyrrhine, nine catarrhines and humans). We show that precision grip and thumb‐lateral behaviours are linked to carpus and thumb length, whereas power grasping is linked to second and third digit length. No phylogenetic signal was found in the behavioural characters when using squared‐change parsimony and phylogenetic eigenvector regression, but such a signal was found in morphometric characters. Our findings shed new light on previously proposed models of the evolution of grasping. Inference models suggest that Australopithecus, Oreopithecus and Proconsul used a precision grip.

Getting a grip on the evolution of grasping in musteloid carnivorans: a three-dimensional analysis of forelimb shape.

The ability to grasp and manipulate is often considered a hallmark of hominins and associated with the evolution of their bipedal locomotion and tool use. Yet, many other mammals use their forelimbs to grasp and manipulate objects. Previous investigations have suggested that grasping may be derived from digging behaviour, arboreal locomotion or hunting behaviour. Here, we test the arboreal origin of grasping and investigate whether an arboreal lifestyle could confer a greater grasping ability in musteloid carnivorans. Moreover, we investigate the morphological adaptations related to grasping and the differences between arboreal species with different grasping abilities. We predict that if grasping is derived from an arboreal lifestyle, then the anatomical specializations of the forelimb for arboreality must be similar to those involved in grasping. We further predict that arboreal species with a well‐developed manipulation ability will have articulations that facilitate radio‐ulnar rotation. We use ancestral character state reconstructions of lifestyle and grasping ability to understand the evolution of both traits. Finally, we use a surface sliding semi‐landmark approach capable of quantifying the articulations in their full complexity. Our results largely confirm our predictions, demonstrating that musteloids with greater grasping skills differ markedly from others in the shape of their forelimb bones. These analyses further suggest that the evolution of an arboreal lifestyle likely preceded the development of enhanced grasping ability.

Food prehension and manipulation in Microcebus murinus (Prosimii, Cheirogaleidae).

Among primates, apes and monkeys are known to use their hands and to exhibit independent control of their fingers. In comparison, Prosimii are thought to have less digital individualization and to use their mouth more commonly for prehension. Unfortunately, prehension and manipulation studies in Prosimii have been conducted in conditions constraining the subject to grasp with the hand. Moreover, the effect of food size remains unexplored, even though it could affect the use of the hands versus the mouth. Thus, whether prosimians use the hand or the mouth to grasp and manipulate food items of different sizes in unconstrained conditions remains unclear. To address this question, we characterized the eating and manipulation patterns of Microcebus murinus in unconstrained conditions, using three food sizes. The results showed that M. murinus showed (i) an eating pattern similar to that of rodents, with smaller food items being grasped with the mouth, (ii) a greater tendency to use the hands for prehension of larger foods, and (iii) plasticity during food manipulation similar to that which has been observed in rodents. These results are discussed in the framework of grasping in mammals and are used to discuss the origins of prehension in primates.

Use and Manufacture of Tools to Extract Food by Captive Gorilla gorilla gorilla: Experimental Approach

The use and manufacture of tools to extract ants and termites is a welldocumented behaviour in wild chimpanzees [Goodall, 1964; Boesch and Boesch, 1990; Yamakoshi and Yamakoshi, 2004]. In contrast, it has never been observed in other great apes in their natural habitat. In captivity, the use of tools to extract ants and fruits has rarely been described in other primates, except in some New World monkeys, the capuchins [Visalberghi, 1990; Westergaard et al., 1997]. Captive gorillas have been seen using sticks to obtain food that was out of reach and pieces of wood as weapons and projectiles [Natale et al., 1986, 1988; Nakamichi, 1998]. This use, as a prolongation of the arm, is totally different in terms of sensorimotor intelligence from manufacturing tools [Piaget, 1952; Parker and Gibson, 1977]. The aim of this study is to test the ability of captive gorillas to use and manufacture tools for static food extraction.

Unconstrained 3D-kinematics of prehension in five primates: Lemur, capuchin, gorilla, chimpanzee, human

Primates are known for their use of the hand in many activities including food grasping. Yet, most studies concentrate on the type of grip used. Moreover, kinematic studies remain limited to a few investigations of the distal elements in constrained conditions in humans and macaques. In order to improve our understanding of the prehension movement in primates, we analyse here the behavioural strategies (e.g., types of grip, body postures) as well as the 3D kinematics of the whole forelimb and the trunk during the prehension of small static food items in five primate species in unconstrained conditions. All species preferred the quadrupedal posture except lemurs, which used a typical crouched posture. Grasp type differed among species, with smaller animals (capuchins and lemurs) using a whole-hand grip and larger animals (humans, gorillas, chimpanzees) using predominantly a precision grip. Larger animals had lower relative wrist velocities and spent a larger proportion of the movement decelerating. Humans grasped food items with planar motions involving small joint rotations, more similar to the smaller animals than to gorillas and chimpanzees, which used greater rotations of both the shoulder and forearm. In conclusion, the features characterising human food prehension are present in other primates, yet differences exist in joint motions. These results provide a good basis to suggest hypotheses concerning the factors involved in driving the evolution of grasping abilities in primates.

Hindlimb interarticular coordinations in Microcebus murinus in maximal leaping.

SUMMARY The purpose of this study was to investigate the pattern of coordinations of the hindlimb joints in the worlds smallest living primate (Microcebus murinus). The sequencing and timing of joint rotations have been analyzed in five adult males performing maximal leaping from a take-off immobile platform to their own wooden nest. Angular kinematics of hip, knee, angle and metatarso-phalangeal (MT) joints were deduced from high-speed X-ray films in the sagittal plane of the animals. The body mass center (BMC) of the lemurs was assimilated to their iliac crest. The maximal airborne performance of the lemurs was 0.33±0.04 m, which represented 2.55±0.36 times their snout–vent length. Take-off instant occurred 72±7 ms after the start of the push-off, with a BMC velocity of 3.23±0.48 m s−1, oriented 55±14 deg. with the horizontal plane. The kinematic analysis of the joints and musculo-tendon architecture of the M. murinus plantar flexors pointed out mechanical power amplifier mechanisms (i.e. stretch-shortening cycle of hindlimb muscles and proximo-to-distal sequence).

Influence of the Task on Hand Preference: Individual Differences among Gorillas (Gorilla gorilla gorilla)

The degree of task complexity and bimanual complementarity have been proposed as factors affecting lateralization strength in humans. However, a large number of studies have demonstrated group-level lateral hand bias for different manual activities in numerous non-human primate species. However, no study has tested the effects that a variety of tasks may have in inducing differences in hand preference. Here, we aim to test if 3 adult gorillas exhibited a greater hand preference bias performing 4 tasks of varying complexity: grasping small versus large foods, proto-tool use task and tool use task involving greater visuospatial requirements. We found that (1) the complexity of the task does not necessarily induce a right-handed bias and (2) a subject can be right-handed for a complex task and left-handed for another one. These results, complemented by many publications on hand preference in non-human primates, reveal a great variability in hand preference, which makes it very difficult to deduce any details of hominin handedness with artefacts.

Estimating thumb–index finger precision grip and manipulation potential in extant and fossil primates

Primates, and particularly humans, are characterized by superior manual dexterity compared with other mammals. However, drawing the biomechanical link between hand morphology/behaviour and functional capabilities in non-human primates and fossil taxa has been challenging. We present a kinematic model of thumb–index precision grip and manipulative movement based on bony hand morphology in a broad sample of extant primates and fossil hominins. The model reveals that both joint mobility and digit proportions (scaled to hand size) are critical for determining precision grip and manipulation potential, but that having either a long thumb or great joint mobility alone does not necessarily yield high precision manipulation. The results suggest even the oldest available fossil hominins may have shared comparable precision grip manipulation with modern humans. In particular, the predicted human-like precision manipulation of Australopithecus afarensis, approximately one million years before the first stone tools, supports controversial archaeological evidence of tool-use in this taxon.