The evolution and biological correlates of hand preferences in anthropoid primates

Limb preferences in non-human vertebrates: A new decade

Over a decade ago, we demonstrated that population-level asymmetries in limb preferences are not uniquely human but occur in various species of non-human animals (Ströckens, F., Güntürkün, O., & Ocklenburg, S. (2013). Limb preferences in non-human vertebrates. Laterality, 18(5), 536-575). While back then, vertebrate limb preference data were too scarce to reconstruct the evolutionary basis of human handedness or apply phylogenetic comparative methods, many voids were filled in the meantime. It is therefore high time to update the last analysis on limb preferences in all non-extinct vertebrate orders in the present article. We show that the robustness of empirical evidence for limb preference in non-human vertebrates increased in the last decade due to (1) more studies, (2) larger sample sizes, and (3) an increased number of meta-analyses integrating findings from various species (e.g., cats, dogs, rats, mice). Similar to the previous publication, we used cladographic comparisons to systematically assess limb preferences in non-extinct vertebrate orders. The identified studies analyzed 172 different species. Overall, 39.53% of species showed evidence for population-level asymmetries, 32.56% showed individual-level asymmetries, and 27.91% showed no asymmetry. These findings not only further support the notion that asymmetries are a widespread feature of vertebrate motor organization, but they also identify crucial gaps that should be filled by future investigations.

A New Method for Whole Bone Analysis of Bilateral Asymmetry

Postcranial asymmetry of bones has been mostly studied with linear or angular measurements. Although conclusive, these measurements fail to capture the differences of the entire bone surface. Here, we develop a methodology to measure whole bone bilateral asymmetry from 3D models. We demonstrate the method using the humerus and the second metacarpal. We compare right and left bones of the same individual (bilateral variation) to that of different scans of the same bone (interscan variation) and of the same bone from different individuals (interindividual variation) to show that the method functions and is able to segregate different degrees of variation. The interscan variation is the lowest, while the interindividual variation is the greatest, and the bilateral variation falls between the other two. Visual comparisons, using color maps, illustrate on the bone where the asymmetry is most marked. As expected, the interscan comparisons show very little variation in shape, while the interindividual comparisons reveal extensive variation. In bilateral comparisons, some patterns were observed. In the humerus, the radial groove, the deltoid tuberosity, and the olecranon fossa were usually the most asymmetrical regions. The epiphyses are also more asymmetrical than the diaphysis. For the MC2, the attachments for the palmar interossei muscles and the articular facets with the MC3 were the most asymmetrical regions. These results demonstrate that this new method helps identify areas of asymmetry that would otherwise be difficult to observe.

Planum Temporale Asymmetries in Primates: A Comparative Study in Great Apes and Monkeys

OBJECTIVES

Most human brains exhibit left hemisphere asymmetry for planum temporale (PT) surface area and gray matter volume, which is interpreted as cerebral lateralization for language. Once considered a uniquely human feature, PT asymmetries have now been documented in chimpanzees and olive baboons. The goal of the current study was to further investigate the evolution of PT asymmetries in nonhuman primates.

MATERIALS AND METHODS

We measured PT surface area in chimpanzees (Pan troglodytes, n = 90), bonobos (Pan paniscus, n = 21), gorillas (Gorilla gorilla, n = 34), orangutans (Pongo spp., n = 33), olive baboons (Papio anubis, n = 105), rhesus macaques (Macaca mulatta, n = 144), and tufted capuchins (Sapajus apella, n = 29) from magnetic resonance imaging scans.

RESULTS

Our findings reveal significant leftward biases in PT surface area among chimpanzees, gorillas, olive baboons, rhesus macaques, and capuchins. We did not find significant population-level asymmetries among orangutans and bonobos, which could be due, in part, to small sample sizes. We also detected significant age effects for rhesus macaques only, and no significant sex effects for any species.

DISCUSSION

The observation of a population-level leftward bias for PT surface area among not only hominids (chimpanzees and gorillas), but also two cercopithecoids (olive baboons and rhesus macaques) and one platyrrhine (tufted capuchins) suggests that PT lateralization was likely present in some early anthropoid primate ancestors and relatives. This provides further evidence that human brains have since undergone changes to the size and connectivity of the PT in response to selection for the cognitive processes needed to support the evolution of language and speech.

Handedness and brain asymmetries in nonhuman primates

A majority of humans are right-handed and exhibit left hemisphere specialization for the comprehension and production of language. To what extent population-level behavioral and brain asymmetries are unique to humans remains a topic of interest across a wide range of scientific disciplines. In this chapter, we present current findings on the expression of population-level behavioral and brain asymmetries in nonhuman primates. We further present data on the association between communication functions, and especially gestures and individual variation in neuroanatomic asymmetries in nonhuman primates, with an emphasis on data from chimpanzees and baboons. The collective data are interpreted within the context of different theories on the evolution of language lateralization.

Brain bilateral asymmetry - insights from nematodes, zebrafish, and Drosophila

Chirality is a fundamental trait of living organisms, encompassing the homochirality of biological molecules and the left-right (LR) asymmetry of visceral organs and the brain. The nervous system in bilaterian organisms displays a lateralized organization characterized by the presence of asymmetrical neuronal circuits and brain functions that are predominantly localized within one hemisphere. Although body asymmetry is relatively well understood, and exhibits robust phenotypic expression and regulation via conserved molecular mechanisms across phyla, current findings indicate that the asymmetry of the nervous system displays greater phenotypic, genetic, and evolutionary variability. In this review we explore the use of nematode, zebrafish, and Drosophila genetic models to investigate neuronal circuit asymmetry. We discuss recent discoveries in the context of body-brain concordance and highlight the distinct characteristics of nervous system asymmetry and its cognitive correlates.

Kin selection as a modulator of human handedness: sex-specific, parental and parent-of-origin effects

The frequency of left-handedness in humans is ~10% worldwide and slightly higher in males than females. Twin and family studies estimate the heritability of human handedness at around 25%. The low but substantial frequency of left-handedness has been suggested to imply negative frequency-dependent selection, e.g. owing to a 'surprise' advantage of left-handers in combat against opponents more used to fighting right-handers. Because such game-theoretic hypotheses involve social interaction, here we perform an analysis of the evolution of handedness based on kin-selection, which is understood to play a major role in the evolution of social behaviour generally. We show that: (1) relatedness modulates the balance of right-handedness vs. left-handedness, according to whether left-handedness is marginally selfish vs. marginally altruistic; (2) sex differences in relatedness to social partners may drive sex differences in handedness; (3) differential relatedness of parents and offspring may generate parent-offspring conflict and sexual conflict leading to the evolution of maternal and paternal genetic effects in relation to handedness; and (4) differential relatedness of maternal-origin vs. paternal-origin genes may generate intragenomic conflict leading to the evolution of parent-of-origin-specific gene effects - such as 'genomic imprinting' - and associated maladaptation.

Handedness in Animals and Plants

Structural and functional asymmetries are traceable in every form of life, and some lateralities are homologous. Functionally speaking, the division of labour between the two halves of the brain is a basic characteristic of the nervous system that arose even before the appearance of vertebrates. The most well-known expression of this specialisation in humans is hand dominance, also known as handedness. Even if hand/limb/paw dominance is far more commonly associated with the presence of a nervous system, it is also observed in its own form in aneural organisms, such as plants. To date, little is known regarding the possible functional significance of this dominance in plants, and many questions remain open (among them, whether it reflects a generalised behavioural asymmetry). Here, we propose a comparative approach to the study of handedness, including plants, by taking advantage of the experimental models and paradigms already used to study laterality in humans and various animal species. By taking this approach, we aim to enrich our knowledge of the concept of handedness across natural kingdoms.

Phylogenetic differences in the morphology and shape of the central sulcus in great apes and humans: implications for the evolution of motor functions

The central sulcus divides the primary motor and somatosensory cortices in many anthropoid primate brains. Differences exist in the surface area and depth of the central sulcus along the dorso-ventral plane in great apes and humans compared to other primate species. Within hominid species, there are variations in the depth and aspect of their hand motor area, or knob, within the precentral gyrus. In this study, we used post-image analyses on magnetic resonance images to characterize the central sulcus shape of humans, chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla), and orangutans (Pongo pygmaeus and Pongo abelii). Using these data, we examined the morphological variability of central sulcus in hominids, focusing on the hand region, a significant change in human evolution. We show that the central sulcus shape differs between great ape species, but all show similar variations in the location of their hand knob. However, the prevalence of the knob location along the dorso-ventral plane and lateralization differs between species and the presence of a second ventral motor knob seems to be unique to humans. Humans and orangutans exhibit the most similar and complex central sulcus shapes. However, their similarities may reflect divergent evolutionary processes related to selection for different positional and habitual locomotor functions.

Roles of Handedness and Hemispheric Lateralization: Implications for Rehabilitation of the Central and Peripheral Nervous Systems: A Rapid Review

IMPORTANCE

Handedness and motor asymmetry are important features of occupational performance. With an increased understanding of the basic neural mechanisms surrounding handedness, clinicians will be better able to implement targeted, evidence-based neurorehabilitation interventions to promote functional independence.

OBJECTIVE

To review the basic neural mechanisms behind handedness and their implications for central and peripheral nervous system injury.

DATA SOURCES

Relevant published literature obtained via MEDLINE.

FINDINGS

Handedness, along with performance asymmetries observed between the dominant and nondominant hands, may be due to hemispheric specializations for motor control. These specializations contribute to predictable motor control deficits that are dependent on which hemisphere or limb has been affected. Clinical practice recommendations for occupational therapists and other rehabilitation specialists are presented.

CONCLUSIONS AND RELEVANCE

It is vital that occupational therapists and other rehabilitation specialists consider handedness and hemispheric lateralization during evaluation and treatment. With an increased understanding of the basic neural mechanisms surrounding handedness, clinicians will be better able to implement targeted, evidence-based neurorehabilitation interventions to promote functional independence. Plain-Language Summary: The goal of this narrative review is to increase clinicians' understanding of the basic neural mechanisms related to handedness (the tendency to select one hand over the other for specific tasks) and their implications for central and peripheral nervous system injury and rehabilitation. An enhanced understanding of these mechanisms may allow clinicians to better tailor neurorehabilitation interventions to address motor deficits and promote functional independence.

Hand preference in wild crab-eating capuchin monkeys (Sapajus libidinosus) in the coastal area of Northest Brazil

Handedness is a fundamental human trait, although recent research, especially on nonhuman primates, has shown that it is displayed by other animals as well (e.g., chimpanzees, gorillas). In this study, we explore hand preference in wild crab-eating tufted capuchin monkeys (Sapajus libidinosus) inhabiting a mangrove forest located on the coastal area of Northeast Brazil (Maranhão State). Tufted capuchin monkeys at our site use facultatively wooden tools to crack open crabs. We observed hand preference in 12 subjects who spontaneously participated in experiment sessions, in which we provided crabs and tools on wooden platforms. We recorded (using events and bouts) two unimanual tasks, (tool or crab) grabbing and (tool or crab) pounding, and one bimanual task, crab pulling, where one hand kept the crab in place while the other pulled off parts of the crab. Hand preference increased with greater strength needed to perform the task and its complexity. While only 17%-25% of capuchins showed hand preference during grabbing, 44%-64% showed hand preference during pounding, and most subjects 64%-80% displayed a right-hand preference when performing the bimanual task, for which all lateralized individuals were right-handed. Hand preference did not vary between adults and juvenile individuals and was not consistent across tasks. Group-level hand preference was found only for the bimanual task, for which all lateralized individuals were right-handed. Our findings are in concordance with those of other primate studies showing the emergence of hemispheric specialization for bimanual actions, highlight the importance of conducting such studies on diverse type of tasks, and show the feasibility to conduct experimental manipulation under natural conditions.

Thalamic neurons drive distinct forms of motor asymmetry that are conserved in teleost and dependent on visual evolution

Brain laterality is a prominent feature in Bilateria, where neural functions are favored in a single brain hemisphere. These hemispheric specializations are thought to improve behavioral performance and are commonly observed as sensory or motor asymmetries, such as handedness in humans. Despite its prevalence, our understanding of the neural and molecular substrates instructing functional lateralization is limited. Moreover, how functional lateralization is selected for or modulated throughout evolution is poorly understood. While comparative approaches offer a powerful tool for addressing this question, a major obstacle has been the lack of a conserved asymmetric behavior in genetically tractable organisms. Previously, we described a robust motor asymmetry in larval zebrafish. Following the loss of illumination, individuals show a persistent turning bias that is associated with search pattern behavior with underlying functional lateralization in the thalamus. This behavior permits a simple yet robust assay that can be used to address fundamental principles underlying lateralization in the brain across taxa. Here, we take a comparative approach and show that motor asymmetry is conserved across diverse larval teleost species, which have diverged over the past 200 million years. Using a combination of transgenic tools, ablation, and enucleation, we show that teleosts exhibit two distinct forms of motor asymmetry, vision-dependent and - independent. These asymmetries are directionally uncorrelated, yet dependent on the same subset of thalamic neurons. Lastly, we leverage Astyanax sighted and blind morphs, which show that fish with evolutionarily derived blindness lack both retinal-dependent and -independent motor asymmetries, while their sighted surface conspecifics retained both forms. Our data implicate that overlapping sensory systems and neuronal substrates drive functional lateralization in a vertebrate brain that are likely targets for selective modulation during evolution.